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  • Codeigniter: Make field increase by 1 up to a number?

    - by Kevin Brown
    In my validation class I have this: $fields['a_1'] = 'First Question'; $fields['a_2'] = 'Second Question'; $fields['a_3'] = 'Third Question'; $fields['a_4'] = 'Fourth Question'; This is getting old--I have about 40 of these to write, and each set has matching validation rules: $rules['a_1'] = 'hour'; $rules['a_2'] = 'hour'; ... Is there a way to say: $fields['a_' . 1 - 17] = "One, Two" Etc... Just curious... if not, I'll brute force it.

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  • Getting ClassCastException with JSF 1.2 Custom Component and BEA 10.3

    - by Tobi
    Im getting a ClassCastException if i use Attributes in my Custom Headline Tag. Without Attributes rendering works fine. Calling <t:headline value="test" /> gives a ClassCastException even before a Method in my HeadlineComponent or HeadlineTag-Class is called. <t:headline /> works fine. I'm using MyFaces-1.2, on BEA 10.3 default.jsp <%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <%@ taglib prefix="f" uri="http://java.sun.com/jsf/core"%> <%@ taglib prefix="h" uri="http://java.sun.com/jsf/html"%> <%@ taglib prefix="t" uri="http://www.tobi.de/taglibrary" %> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>Tobi Test</title> </head> <body> <f:view> <t:headline value="test" /> </f:view> </body> </html> HeadlineComponent.java package tobi.web.component.headline; import java.io.IOException; import javax.el.ValueExpression; import javax.faces.component.UIOutput; import javax.faces.context.FacesContext; import javax.faces.context.ResponseWriter; public class HeadlineComponent extends UIOutput { private String value; private Integer size; @Override public Object saveState(FacesContext context) { Object values[] = new Object[3]; values[0] = super.saveState(context); values[1] = value; values[2] = size; return ((Object)(values)); } @Override public void restoreState(FacesContext context, Object state) { Object values[] = (Object[])state; super.restoreState(context, values[0]); value = (String)values[1]; size = (Integer)values[2]; } @Override public void encodeBegin(FacesContext context) throws IOException { // Wenn keine Groesse angegeben wurde default 3 String htmlTag = (size == null) ? "h3" : "h"+getSize().toString(); ResponseWriter writer = context.getResponseWriter(); writer.startElement(htmlTag, this); if(value == null) { writer.write(""); } else { writer.write(value); } writer.endElement(htmlTag); writer.flush(); } public String getValue() { if(value != null) { return value; } ValueExpression ve = getValueExpression("value"); if(ve != null) { return (String)ve.getValue(getFacesContext().getELContext()); } return null; } public void setValue(String value) { this.value = value; } public Integer getSize() { if(size != null) { return size; } ValueExpression ve = getValueExpression("size"); if(ve != null) { return (Integer)ve.getValue(getFacesContext().getELContext()); } return null; } public void setSize(Integer size) { if(size>6) size = 6; if(size<1) size = 1; this.size = size; } } HeadlineTag.java package tobi.web.component.headline; import javax.el.ValueExpression; import javax.faces.component.UIComponent; import javax.faces.webapp.UIComponentELTag; public class HeadlineTag extends UIComponentELTag { private ValueExpression value; private ValueExpression size; @Override public String getComponentType() { return "tobi.headline"; } @Override public String getRendererType() { // null, da wir hier keinen eigenen Render benutzen return null; } protected void setProperties(UIComponent component) { super.setProperties(component); HeadlineComponent headline = (HeadlineComponent)component; if(value != null) { if(value.isLiteralText()) { headline.getAttributes().put("value", value.getExpressionString()); } else { headline.setValueExpression("value", value); } } if(size != null) { if(size.isLiteralText()) { headline.getAttributes().put("size", size.getExpressionString()); } else { headline.setValueExpression("size", size); } } } @Override public void release() { super.release(); this.value = null; this.size = null; } public ValueExpression getValue() { return value; } public void setValue(ValueExpression value) { this.value = value; } public ValueExpression getSize() { return size; } public void setSize(ValueExpression size) { this.size = size; } } taglibrary.tld <?xml version="1.0" encoding="UTF-8" ?> <taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd" version="2.1"> <description>Tobi Webclient Taglibrary</description> <tlib-version>1.0</tlib-version> <short-name>tobi-taglibrary</short-name> <uri>http://www.tobi.de/taglibrary</uri> <tag> <description>Eine Überschrift im HTML-Stil</description> <name>headline</name> <tag-class>tobi.web.component.headline.HeadlineTag</tag-class> <body-content>empty</body-content> <attribute> <description>Der Text der Überschrift</description> <name>value</name> <required>false</required> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <description>Die Größe der Überschrift nach HTML (h1 - h6)</description> <name>size</name> <required>false</required> <rtexprvalue>true</rtexprvalue> </attribute> </tag> </taglib> faces-config.xml <?xml version="1.0" encoding="UTF-8"?> <faces-config xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_1_2.xsd" version="1.2"> <component> <description>Erzeugt eine Überschrift nach HTML-Stil</description> <display-name>headline</display-name> <component-type>tobi.headline</component-type> <component-class>tobi.web.component.headline.HeadlineComponent</component-class> <attribute> <attribute-name>value</attribute-name> <attribute-class>java.lang.String</attribute-class> </attribute> <attribute> <attribute-name>size</attribute-name> <attribute-class>java.lang.Integer</attribute-class> <default-value>3</default-value> </attribute> </component> </faces-config>

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  • Adding Polynomials (Linked Lists)......Bug Help

    - by Brian
    I have written a program that creates nodes that in this class are parts of polynomials and then the two polynomials get added together to become one polynomial (list of nodes). All my code compiles so the only problem I am having is that the nodes are not inserting into the polynomial via the insert method I have in polynomial.java and when running the program it does create nodes and displays them in the 2x^2 format but when it comes to add the polynomials together it displays o as the polynomials, so if anyone can figure out whats wrong and what I can do to fix it it would be much appreciated. Here is the code: import java.util.Scanner; class Polynomial{ public termNode head; public Polynomial() { head = null; } public boolean isEmpty() { return (head == null); } public void display() { if (head == null) System.out.print("0"); else for(termNode cur = head; cur != null; cur = cur.getNext()) { System.out.println(cur); } } public void insert(termNode newNode) { termNode prev = null; termNode cur = head; while (cur!=null && (newNode.compareTo(cur)<0)) { prev = null; cur = cur.getNext(); } if (prev == null) { newNode.setNext(head); head = newNode; } else { newNode.setNext(cur); prev.setNext(newNode); } } public void readPolynomial(Scanner kb) { boolean done = false; double coefficient; int exponent; termNode term; head = null; //UNLINK ANY PREVIOUS POLYNOMIAL System.out.println("Enter 0 and 0 to end."); System.out.print("coefficient: "); coefficient = kb.nextDouble(); System.out.println(coefficient); System.out.print("exponent: "); exponent = kb.nextInt(); System.out.println(exponent); done = (coefficient == 0 && exponent == 0); while(!done) { Polynomial poly = new Polynomial(); term = new termNode(coefficient,exponent); System.out.println(term); poly.insert(term); System.out.println("Enter 0 and 0 to end."); System.out.print("coefficient: "); coefficient = kb.nextDouble(); System.out.println(coefficient); System.out.print("exponent: "); exponent = kb.nextInt(); System.out.println(exponent); done = (coefficient==0 && exponent==0); } } public static Polynomial add(Polynomial p, Polynomial q) { Polynomial r = new Polynomial(); double coefficient; int exponent; termNode first = p.head; termNode second = q.head; termNode sum = r.head; termNode term; while (first != null && second != null) { if (first.getExp() == second.getExp()) { if (first.getCoeff() != 0 && second.getCoeff() != 0); { double addCoeff = first.getCoeff() + second.getCoeff(); term = new termNode(addCoeff,first.getExp()); sum.setNext(term); first.getNext(); second.getNext(); } } else if (first.getExp() < second.getExp()) { sum.setNext(second); term = new termNode(second.getCoeff(),second.getExp()); sum.setNext(term); second.getNext(); } else { sum.setNext(first); term = new termNode(first.getNext()); sum.setNext(term); first.getNext(); } } while (first != null) { sum.setNext(first); } while (second != null) { sum.setNext(second); } return r; } } Here is my Node class: class termNode implements Comparable { private int exp; private double coeff; private termNode next; public termNode(double coefficient, int exponent) { coeff = coefficient; exp = exponent; next = null; } public termNode(termNode inTermNode) { coeff = inTermNode.coeff; exp = inTermNode.exp; } public void setData(double coefficient, int exponent) { coefficient = coeff; exponent = exp; } public double getCoeff() { return coeff; } public int getExp() { return exp; } public void setNext(termNode link) { next = link; } public termNode getNext() { return next; } public String toString() { if (exp == 0) { return(coeff + " "); } else if (exp == 1) { return(coeff + "x"); } else { return(coeff + "x^" + exp); } } public int compareTo(Object other) { if(exp ==((termNode) other).exp) return 0; else if(exp < ((termNode) other).exp) return -1; else return 1; } } And here is my Test class to run the program. import java.util.Scanner; class PolyTest{ public static void main(String [] args) { Scanner kb = new Scanner(System.in); Polynomial r; Polynomial p = new Polynomial(); System.out.println("Enter first polynomial."); p.readPolynomial(kb); Polynomial q = new Polynomial(); System.out.println(); System.out.println("Enter second polynomial."); q.readPolynomial(kb); r = Polynomial.add(p,q); System.out.println(); System.out.print("The sum of "); p.display(); System.out.print(" and "); q.display(); System.out.print(" is "); r.display(); } }

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  • C#: Inheritance, Overriding, and Hiding

    - by Rosarch
    I'm having difficulty with an architectural decision for my C# XNA game. The basic entity in the world, such as a tree, zombie, or the player, is represented as a GameObject. Each GameObject is composed of at least a GameObjectController, GameObjectModel, and GameObjectView. These three are enough for simple entities, like inanimate trees or rocks. However, as I try to keep the functionality as factored out as possible, the inheritance begins to feel unwieldy. Syntactically, I'm not even sure how best to accomplish my goals. Here is the GameObjectController: public class GameObjectController { protected GameObjectModel model; protected GameObjectView view; public GameObjectController(GameObjectManager gameObjectManager) { this.gameObjectManager = gameObjectManager; model = new GameObjectModel(this); view = new GameObjectView(this); } public GameObjectManager GameObjectManager { get { return gameObjectManager; } } public virtual GameObjectView View { get { return view; } } public virtual GameObjectModel Model { get { return model; } } public virtual void Update(long tick) { } } I want to specify that each subclass of GameObjectController will have accessible at least a GameObjectView and GameObjectModel. If subclasses are fine using those classes, but perhaps are overriding for a more sophisticated Update() method, I don't want them to have to duplicate the code to produce those dependencies. So, the GameObjectController constructor sets those objects up. However, some objects do want to override the model and view. This is where the trouble comes in. Some objects need to fight, so they are CombatantGameObjects: public class CombatantGameObject : GameObjectController { protected new readonly CombatantGameModel model; public new virtual CombatantGameModel Model { get { return model; } } protected readonly CombatEngine combatEngine; public CombatantGameObject(GameObjectManager gameObjectManager, CombatEngine combatEngine) : base(gameObjectManager) { model = new CombatantGameModel(this); this.combatEngine = combatEngine; } public override void Update(long tick) { if (model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); } base.Update(tick); } } Still pretty simple. Is my use of new to hide instance variables correct? Note that I'm assigning CombatantObjectController.model here, even though GameObjectController.Model was already set. And, combatants don't need any special view functionality, so they leave GameObjectController.View alone. Then I get down to the PlayerController, at which a bug is found. public class PlayerController : CombatantGameObject { private readonly IInputReader inputReader; private new readonly PlayerModel model; public new PlayerModel Model { get { return model; } } private float lastInventoryIndexAt; private float lastThrowAt; public PlayerController(GameObjectManager gameObjectManager, IInputReader inputReader, CombatEngine combatEngine) : base(gameObjectManager, combatEngine) { this.inputReader = inputReader; model = new PlayerModel(this); Model.Health = Constants.PLAYER_HEALTH; } public override void Update(long tick) { if (Model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); for (int i = 0; i < 10; i++) { Debug.WriteLine("YOU DEAD SON!!!"); } return; } UpdateFromInput(tick); // .... } } The first time that this line is executed, I get a null reference exception: model.Body.ApplyImpulse(movementImpulse, model.Position); model.Position looks at model.Body, which is null. This is a function that initializes GameObjects before they are deployed into the world: public void Initialize(GameObjectController controller, IDictionary<string, string> data, WorldState worldState) { controller.View.read(data); controller.View.createSpriteAnimations(data, _assets); controller.Model.read(data); SetUpPhysics(controller, worldState, controller.Model.BoundingCircleRadius, Single.Parse(data["x"]), Single.Parse(data["y"]), bool.Parse(data["isBullet"])); } Every object is passed as a GameObjectController. Does that mean that if the object is really a PlayerController, controller.Model will refer to the base's GameObjectModel and not the PlayerController's overriden PlayerObjectModel? In response to rh: This means that now for a PlayerModel p, p.Model is not equivalent to ((CombatantGameObject)p).Model, and also not equivalent to ((GameObjectController)p).Model. That is exactly what I do not want. I want: PlayerController p; p.Model == ((CombatantGameObject)p).Model p.Model == ((GameObjectController)p).Model How can I do this? override?

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  • Drupal Customizing User Registration Form

    - by Asif Mulla
    Hi All, I am newbie in Drupal 6. I am looking for customizing User registration form. Apparently found that while adding user using Admin login allows registration form to have fields like email address, username, password,confirm password, etc with validations. But when anonymous use wants to register, then only fields like email address and username are displayed. I tried with Profile module available. But now how could I add some fields (password, confirm password, terms & condition check and receive news letter check box)and behavior (password, confirm password validation etc.)? If I am adding such fields they are also get visible in AdminAdd user form resulting duplicate fields like Password,Confirm password. Could you please suggest me how can I do this? I tried googling but confused me a lot as I am beginner to Drupal.

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  • Android draw using SurfaceView and Thread

    - by Morten Høgseth
    I am trying to draw a ball to my screen using 3 classes. I have read a little about this and I found a code snippet that works using the 3 classes on one page, Playing with graphics in Android I altered the code so that I have a ball that is moving and shifts direction when hitting the wall like the picture below (this is using the code in the link). Now I like to separate the classes into 3 different pages for not making everything so crowded, everything is set up the same way. Here are the 3 classes I have. BallActivity.java Ball.java BallThread.java package com.brick.breaker; import android.app.Activity; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class BallActivity extends Activity { private Ball ball; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); ball = new Ball(this); setContentView(ball); } @Override protected void onPause() { // TODO Auto-generated method stub super.onPause(); setContentView(null); ball = null; finish(); } } package com.brick.breaker; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.view.SurfaceHolder; import android.view.SurfaceView; public class Ball extends SurfaceView implements SurfaceHolder.Callback { private BallThread ballThread = null; private Bitmap bitmap; private float x, y; private float vx, vy; public Ball(Context context) { super(context); // TODO Auto-generated constructor stub bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ball); x = 50.0f; y = 50.0f; vx = 10.0f; vy = 10.0f; getHolder().addCallback(this); ballThread = new BallThread(getHolder(), this); } protected void onDraw(Canvas canvas) { update(canvas); canvas.drawBitmap(bitmap, x, y, null); } public void update(Canvas canvas) { checkCollisions(canvas); x += vx; y += vy; } public void checkCollisions(Canvas canvas) { if(x - vx < 0) { vx = Math.abs(vx); } else if(x + vx > canvas.getWidth() - getBitmapWidth()) { vx = -Math.abs(vx); } if(y - vy < 0) { vy = Math.abs(vy); } else if(y + vy > canvas.getHeight() - getBitmapHeight()) { vy = -Math.abs(vy); } } public int getBitmapWidth() { if(bitmap != null) { return bitmap.getWidth(); } else { return 0; } } public int getBitmapHeight() { if(bitmap != null) { return bitmap.getHeight(); } else { return 0; } } public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { // TODO Auto-generated method stub } public void surfaceCreated(SurfaceHolder holder) { // TODO Auto-generated method stub ballThread.setRunnable(true); ballThread.start(); } public void surfaceDestroyed(SurfaceHolder holder) { // TODO Auto-generated method stub boolean retry = true; ballThread.setRunnable(false); while(retry) { try { ballThread.join(); retry = false; } catch(InterruptedException ie) { //Try again and again and again } break; } ballThread = null; } } package com.brick.breaker; import android.graphics.Canvas; import android.view.SurfaceHolder; public class BallThread extends Thread { private SurfaceHolder sh; private Ball ball; private Canvas canvas; private boolean run = false; public BallThread(SurfaceHolder _holder,Ball _ball) { sh = _holder; ball = _ball; } public void setRunnable(boolean _run) { run = _run; } public void run() { while(run) { canvas = null; try { canvas = sh.lockCanvas(null); synchronized(sh) { ball.onDraw(canvas); } } finally { if(canvas != null) { sh.unlockCanvasAndPost(canvas); } } } } public Canvas getCanvas() { if(canvas != null) { return canvas; } else { return null; } } } Here is a picture that shows the outcome of these classes. I've tried to figure this out but since I am pretty new to Android development I thought I could ask for help. Does any one know what is causing the ball to be draw like that? The code is pretty much the same as the one in the link and I have tried to experiment to find a solution but no luck. Thx in advance for any help=)

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  • Clone a div that contains "customized" jQueryUI datePicker

    - by Enrique
    I have a div that contains 3 fields You can see the image here http://imgur.com/A3tbd.jpg I'm cloning this div with this plugin http://sroucheray.org/blog/demos/jquery-dynamic-form/ My problems are: It doesn't clone correctly datePicker. I'm using validate form plugin, but I guess this plugin is not prepared to validate cloned elements Is there any easy code, other plugin or some functions I should use for doing this sequence? Verify user has filled the 3 fields of the actual div If so, clone the div and create a new set of 3 fields. Also, clone datePicker correctly If user clicks the delete button, erase last div (last 3 fields) When form submitted, post all fields correctly Thanks,

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  • Maze not generating properly. Out of bounds exception. need quick fix

    - by Dan Joseph Porcioncula
    My maze generator seems to have a problem. I am trying to generate something like the maze from http://mazeworks.com/mazegen/mazetut/index.htm . My program displays this http://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc7/s320x320/374060_426350204045347_100000111130260_1880768_1572427285_n.jpg and the error Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at Grid.genRand(Grid.java:73) at Grid.main(Grid.java:35) How do I fix my generator program? import java.awt.*; import java.awt.Color; import java.awt.Component; import java.awt.Graphics; import javax.swing.*; import java.util.ArrayList; public class Grid extends Canvas { Cell[][] maze; int size; int pathSize; double width, height; ArrayList<int[]> coordinates = new ArrayList<int[]>(); public Grid(int size, int h, int w) { this.size = size; maze = new Cell[size][size]; for(int i = 0; i<size; i++){ for(int a =0; a<size; a++){ maze[i][a] = new Cell(); } } setPreferredSize(new Dimension(h, w)); } public static void main(String[] args) { JFrame y = new JFrame(); y.setLayout(new BorderLayout()); Grid f = new Grid(25, 400, 400); y.add(f, BorderLayout.CENTER); y.setSize(450, 450); y.setVisible(true); y.setDefaultCloseOperation(y.EXIT_ON_CLOSE); f.genRand(); f.repaint(); } public void push(int[] xy) { coordinates.add(xy); int i = coordinates.size(); coordinates.ensureCapacity(i++); } public int[] pop() { int[] x = coordinates.get((coordinates.size())-1); coordinates.remove((coordinates.size())-1); return x; } public int[] top() { return coordinates.get((coordinates.size())-1); } public void genRand(){ // create a CellStack (LIFO) to hold a list of cell locations [x] // set TotalCells = number of cells in grid int TotalCells = size*size; // choose a cell at random and call it CurrentCell int m = randomInt(size); int n = randomInt(size); Cell curCel = maze[m][n]; // set VisitedCells = 1 int visCel = 1,d=0; int[] q; int h,o = 0,p = 0; // while VisitedCells < TotalCells while( visCel < TotalCells){ // find all neighbors of CurrentCell with all walls intact if(maze[m-1][n].countWalls() == 4){d++;} if(maze[m+1][n].countWalls() == 4){d++;} if(maze[m][n-1].countWalls() == 4){d++;} if(maze[m][n+1].countWalls() == 4){d++;} // if one or more found if(d!=0){ Point[] ls = new Point[4]; ls[0] = new Point(m-1,n); ls[1] = new Point(m+1,n); ls[2] = new Point(m,n-1); ls[3] = new Point(m,n+1); // knock down the wall between it and CurrentCell h = randomInt(3); switch(h){ case 0: o = (int)(ls[0].getX()); p = (int)(ls[0].getY()); curCel.destroyWall(2); maze[o][p].destroyWall(1); break; case 1: o = (int)(ls[1].getX()); p = (int)(ls[1].getY()); curCel.destroyWall(1); maze[o][p].destroyWall(2); break; case 2: o = (int)(ls[2].getX()); p = (int)(ls[2].getY()); curCel.destroyWall(3); maze[o][p].destroyWall(0); break; case 3: o = (int)(ls[3].getX()); p = (int)(ls[3].getY()); curCel.destroyWall(0); maze[o][p].destroyWall(3); break; } // push CurrentCell location on the CellStack push(new int[] {m,n}); // make the new cell CurrentCell m = o; n = p; curCel = maze[m][n]; // add 1 to VisitedCells visCel++; } // else else{ // pop the most recent cell entry off the CellStack q = pop(); m = q[0]; n = q[1]; curCel = maze[m][n]; // make it CurrentCell // endIf } // endWhile } } public int randomInt(int s) { return (int)(s* Math.random());} public void paint(Graphics g) { int k, j; width = getSize().width; height = getSize().height; double htOfRow = height / (size); double wdOfRow = width / (size); //checks verticals - destroys east border of cell for (k = 0; k < size; k++) { for (j = 0; j < size; j++) { if(maze[k][j].checkWall(2)){ g.drawLine((int) (k * wdOfRow), (int) (j * htOfRow), (int) (k * wdOfRow), (int) ((j+1) * htOfRow)); }} } //checks horizontal - destroys north border of cell for (k = 0; k < size; k++) { for (j = 0; j < size; j++) { if(maze[k][j].checkWall(3)){ g.drawLine((int) (k * wdOfRow), (int) (j * htOfRow), (int) ((k+1) * wdOfRow), (int) (j * htOfRow)); }} } } } class Cell { private final static int NORTH = 0; private final static int EAST = 1; private final static int WEST = 2; private final static int SOUTH = 3; private final static int NO = 4; private final static int START = 1; private final static int END = 2; boolean[] wall = new boolean[4]; boolean[] border = new boolean[4]; boolean[] backtrack = new boolean[4]; boolean[] solution = new boolean[4]; private boolean isVisited = false; private int Key = 0; public Cell(){ for(int i=0;i<4;i++){wall[i] = true;} } public int countWalls(){ int i, k =0; for(i=0; i<4; i++) { if (wall[i] == true) {k++;} } return k;} public boolean checkWall(int x){ switch(x){ case 0: return wall[0]; case 1: return wall[1]; case 2: return wall[2]; case 3: return wall[3]; } return true; } public void destroyWall(int x){ switch(x){ case 0: wall[0] = false; break; case 1: wall[1] = false; break; case 2: wall[2] = false; break; case 3: wall[3] = false; break; } } public void setStart(int i){Key = i;} public int getKey(){return Key;} public boolean checkVisit(){return isVisited;} public void visitCell(){isVisited = true;} }

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  • Scala and the Java Memory Model

    - by Ben Lings
    The Java Memory Model (since 1.5) treats final fields differently to non-final fields. In particular, provided the this reference doesn't escape during construction, writes to final fields in the constructor are guaranteed to be visible on other threads even if the object is made available to the other thread via a data race. (Writes to non-final fields aren't guaranteed to be visible, so if you improperly publish them, another thread could see them in a partially constructed state.) Is there any documentation on how/if the Scala compiler creates final (rather than non-final) backing fields for classes? I've looked through the language specification and searched the web but can't find any definitive answers. (In comparison the @scala.volatile annotation is documented to mark a field as volatile)

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  • ArrayList access

    - by Ricky McQuesten
    So once again I have a question about this program. I want to store transactions that are made in an arraylist and then have an option in the case menu where I can print out those that are stored. I have been researching online and have been unable to find a solution to this, so is this possible and how would I go about doing this? I also want to attach a timestamp to each transaction as well. Here is the code I have so far. So my question is how would I add a timestamp to each withdrawal or deposit, and how would I store each transaction in array list? import java.util.*; public class BankAccount extends Money { //inheritence static String name; public static int acctNum; public static double balance, amount; BankAccount(String name, int accNo, double bal) { this.name = name; this.acctNum = accNo; this.balance = bal; } void display() { System.out.println("Your Name:" + name); System.out.println("Your Account Number:" + acctNum); System.out.println("Your Current Account Balance:" + Money.getBalance()); } void displayBalance() { System.out.println("Balance:" + balance); } } import java.util.Scanner; /** * * @author Ricky */ public class Money { public static int accountNumber; public static double balance; static double amount; static String name; public void setDeposit(double amount) { balance = balance + amount; if (amount < 0) { System.out.println("Invalid"); } } public double getDeposit() { return 1; } public void setBalance(double b) { balance = b; } public static double getBalance() { return balance; } public void setWithdraw(double amount) { if (balance < amount) { System.out.println("Not enough funds."); } else if(amount < 0) { System.out.println("Invalid"); } else { balance = balance - amount; } } public double getWithdraw() { return 1; } } import java.util.*; public class Client { public static void main(String args[]) { int n = 0; int count; String trans; ArrayList<String> transaction= new ArrayList<String>(n); Scanner input = new Scanner(System.in); System.out.println("Welcome to First National Bank"); System.out.println("Please enter your name: "); String cusName = input.nextLine(); System.out.println("You will now be assigned an account number."); Random randomGenerator = new Random(); int accNo = randomGenerator.nextInt(100000); //random number System.out.println("Your account number is: " + accNo); System.out.println("Please enter your initial account balance: "); Double balance = input.nextDouble(); BankAccount b1 = new BankAccount(cusName, accNo, balance); b1.setBalance(balance); int menu; /*System.out.println("Menu"); System.out.println("1. Deposit Amount"); System.out.println("2. Withdraw Amount"); System.out.println("3. Display Information"); System.out.println("4. Exit");*/ boolean quit = false; do { System.out.println("*******Menu*******"); System.out.println("1. Deposit Amount"); // menu to take input from user System.out.println("2. Withdraw Amount"); System.out.println("3. Display Information"); System.out.println("4. Exit"); System.out.print("Please enter your choice: "); menu = input.nextInt(); switch (menu) { case 1: System.out.print("Enter depost amount:"); b1.setDeposit(input.nextDouble()); b1.getDeposit(); transaction.add(trans); break; case 2: System.out.println("Current Account Balance=" + b1.getBalance()); System.out.print("Enter withdrawal amount:"); b1.setWithdraw(input.nextDouble()); b1.getWithdraw(); transaction.add(trans); break; // switch statments to do a loop case 3: b1.display(); break; case 4: quit = true; break; } } while (!quit); } } public class Date { static Date time = new Date(); }

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  • Dealing with a badly formatted CSV file

    - by Josh K
    I have an exceptionally bad CSV file. Although I "solved" the problem in the end by manually writing scripts to process and reprocess this specific file I wanted to know if there were any other solutions out there. You have a CSV file that has all the fields terminated by | (pipe) characters. Running a quick check shows you that there are 53 fields in the file. The person who gave you the file claims there there are only 28 fields. Not all of the fields have information in them. For example there are five custom_field_{num} fields which may or may not have data. How would you get this into a database nicely? The ideal solution (and one I searched high and low for) would be to just throw it all into a table with no column names or specifications. Then remove any columns that were completely blank and then give them titles and specifications.

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  • Cross Browser input field width stylization

    - by Derek Adair
    Hi, I have a shipping/billing input form and I'm having trouble styling the input fields to be the same width... Here is a link (click one of the order bottles to go to the checkout page which contains the form) The Problem: -a field <input type="text" size="X" /> appears to render with different sizes in different browsers (see link). -In addition, select fields seem to render on a differently as well. -Chrome/safari do not seem to respond to the font-size property for select fields. Any guidance on how to stylize the size of text-input and select fields cross-browser would be oh so very helpful. Must I result to having a different sytlesheet for each browser... just for these input fields? -thanks

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  • Saving image from Gallery to db - Coursor IllegalStateException

    - by MyWay
    I want to save to db some strings with image. Image can be taken from gallery or user can set the sample one. In the other activity I have a listview which should present the rows with image and name. I'm facing so long this problem. It occurs when I wanna display listview with the image from gallery, If the sample image is saved in the row everything works ok. My problem is similar to this one: how to save image taken from camera and show it to listview - crashes with "IllegalStateException" but I can't find there the solution for me My table in db looks like this: public static final String KEY_ID = "_id"; public static final String ID_DETAILS = "INTEGER PRIMARY KEY AUTOINCREMENT"; public static final int ID_COLUMN = 0; public static final String KEY_NAME = "name"; public static final String NAME_DETAILS = "TEXT NOT NULL"; public static final int NAME_COLUMN = 1; public static final String KEY_DESCRIPTION = "description"; public static final String DESCRIPTION_DETAILS = "TEXT"; public static final int DESCRIPTION_COLUMN = 2; public static final String KEY_IMAGE ="image" ; public static final String IMAGE_DETAILS = "BLOP"; public static final int IMAGE_COLUMN = 3; //method which create our table private static final String CREATE_PRODUCTLIST_IN_DB = "CREATE TABLE " + DB_TABLE + "( " + KEY_ID + " " + ID_DETAILS + ", " + KEY_NAME + " " + NAME_DETAILS + ", " + KEY_DESCRIPTION + " " + DESCRIPTION_DETAILS + ", " + KEY_IMAGE +" " + IMAGE_DETAILS + ");"; inserting statement: public long insertToProductList(String name, String description, byte[] image) { ContentValues value = new ContentValues(); // get the id of column and value value.put(KEY_NAME, name); value.put(KEY_DESCRIPTION, description); value.put(KEY_IMAGE, image); // put into db return db.insert(DB_TABLE, null, value); } Button which add the picture and onActivityResult method which saves the image and put it into the imageview public void AddPicture(View v) { // creating specified intent which have to get data Intent intent = new Intent(Intent.ACTION_PICK); // From where we want choose our pictures intent.setType("image/*"); startActivityForResult(intent, PICK_IMAGE); } @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { // TODO Auto-generated method stub super.onActivityResult(requestCode, resultCode, data); // if identification code match to the intent, //if yes we know that is our picture, if(requestCode ==PICK_IMAGE ) { // check if the data comes with intent if(data!= null) { Uri chosenImage = data.getData(); String[] filePathColumn = {MediaStore.Images.Media.DATA}; Cursor cursor = getContentResolver().query(chosenImage, filePathColumn, null, null, null); cursor.moveToFirst(); int columnIndex = cursor.getColumnIndex(filePathColumn[0]); String filePat = cursor.getString(columnIndex); cursor.close(); ImageOfProduct = BitmapFactory.decodeFile(filePat); if(ImageOfProduct!=null) { picture.setImageBitmap(ImageOfProduct); } messageDisplayer("got picture, isn't null " + IdOfPicture); } } } Then the code which converts bitmap to byte[] public byte[] bitmapToByteConvert(Bitmap bit ) { // stream of data getted for compressed bitmap ByteArrayOutputStream gettedData = new ByteArrayOutputStream(); // compressing method bit.compress(CompressFormat.PNG, 0, gettedData); // our byte array return gettedData.toByteArray(); } The method which put data to the row: byte[] image=null; // if the name isn't put to the editView if(name.getText().toString().trim().length()== 0) { messageDisplayer("At least you need to type name of product if you want add it to the DB "); } else{ String desc = description.getText().toString(); if(description.getText().toString().trim().length()==0) { messageDisplayer("the description is set as none"); desc = "none"; } DB.open(); if(ImageOfProduct!= null){ image = bitmapToByteConvert(ImageOfProduct); messageDisplayer("image isn't null"); } else { BitmapDrawable drawable = (BitmapDrawable) picture.getDrawable(); image = bitmapToByteConvert(drawable.getBitmap()); } if(image.length>0 && image!=null) { messageDisplayer(Integer.toString(image.length)); } DB.insertToProductList(name.getText().toString(), desc, image ); DB.close(); messageDisplayer("well done you add the product"); finish(); You can see that I'm checking here the length of array to be sure that I don't send empty one. And here is the place where Error appears imo, this code is from activity which presents the listview with data taken from db private void LoadOurLayoutListWithInfo() { // firstly wee need to open connection with db db= new sqliteDB(getApplicationContext()); db.open(); // creating our custom adaprer, the specification of it will be typed // in our own class (MyArrayAdapter) which will be created below ArrayAdapter<ProductFromTable> customAdapter = new MyArrayAdapter(); //get the info from whole table tablecursor = db.getAllColumns(); if(tablecursor != null) { startManagingCursor(tablecursor); tablecursor.moveToFirst(); } // now we moving all info from tablecursor to ourlist if(tablecursor != null && tablecursor.moveToFirst()) { do{ // taking info from row in table int id = tablecursor.getInt(sqliteDB.ID_COLUMN); String name= tablecursor.getString(sqliteDB.NAME_COLUMN); String description= tablecursor.getString(sqliteDB.DESCRIPTION_COLUMN); byte[] image= tablecursor.getBlob(3); tablefromDB.add(new ProductFromTable(id,name,description,image)); // moving until we didn't find last row }while(tablecursor.moveToNext()); } listView = (ListView) findViewById(R.id.tagwriter_listoftags); //as description says // setAdapter = The ListAdapter which is responsible for maintaining //the data backing this list and for producing a view to represent //an item in that data set. listView.setAdapter(customAdapter); } I put the info from row tho objects which are stored in list. I read tones of question but I can't find any solution for me. Everything works when I put the sample image ( which is stored in app res folder ). Thx for any advice

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  • How to correctly populate records from SQLlite in ListActivity?

    - by Pavel
    Hi. Can someone please tell me how can I easily display every record from sqllite in ListActivity tab? I'm kinda confused with this. Do I have to create db from my helper class in TabActivity or ListActivity or both? My db helper class is as follow: package tabs.app; import android.content.ContentValues; import android.content.Context; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; public class DBAdapter { private static String DB_PATH = "/data/data/tabs.app/databases/"; public static final String KEY_ROWID = "_id"; public static final String KEY_LATITUDE = "latitude"; public static final String KEY_LONGITUDE = "longitude"; private static final String TAG = "DBAdapter"; private static final String DATABASE_NAME = "coords"; private static final String DATABASE_TABLE = "coordsStorages"; private static final int DATABASE_VERSION = 2; /* private static final String DATABASE_CREATE = "create table coordsStorage (_id integer primary key autoincrement, latitude integer not null, longitude integer not null)"; */ public Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db; public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("create table coordsStorages (_id integer primary key autoincrement, latitude integer not null, longitude integer not null)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS titles"); onCreate(db); } } //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; } //---closes the database--- public void close() { DBHelper.close(); } //---insert a title into the database--- public long insertCoords(int latitude, int longitude) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_LATITUDE, latitude); initialValues.put(KEY_LONGITUDE, longitude); return db.insert(DATABASE_TABLE, null, initialValues); } public void openDataBase() throws SQLException{ //Open the database String myPath = DB_PATH + DATABASE_NAME; db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); } //---deletes a particular title--- public boolean deleteTitle(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; } //---retrieves all the titles--- public Cursor getAllTitles() { return db.query(DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, null, null, null, null, null); } //---retrieves a particular title--- public Cursor getTitle(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] { KEY_ROWID, KEY_LATITUDE, KEY_LONGITUDE}, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //---updates a title--- /*public boolean updateTitle(long rowId, int latitude, int longitude) { ContentValues args = new ContentValues(); args.put(KEY_LATITUDE, latitude); args.put(KEY_LONGITUDE, longitude); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; }*/ } And Im trying to retrieve the records in TabActivity like this: public class Areas extends ListActivity { DBAdapter db; SimpleCursorAdapter mAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.areas_layout); db = new DBAdapter(this); db.open(); Cursor c = db.getAllTitles(); startManagingCursor(c); String[] display = new String[] { db.KEY_LATITUDE }; int[] to = new int[] { R.id.row_latitude}; /* String[] display2 = new String[] { db.KEY_LONGITUDE }; int[] to2 = new int[] { R.id.row_longitude};*/ mAdapter = new SimpleCursorAdapter(this, R.layout.areas_layout, c, display, to); setListAdapter(mAdapter); /* mAdapter2 = new SimpleCursorAdapter(this, R.layout.areas_layout, c, display2, to2); setListAdapter(mAdapter2);*/ db.close(); } /* private void fillData() { // Get all of the rows from the database and create the item list Cursor c = db.getAllTitles(); startManagingCursor(c); }*/ } Whenever I'm trying to do that the error log outputs this: 06-07 09:51:56.529: ERROR/AndroidRuntime(2034): Uncaught handler: thread main exiting due to uncaught exception 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): java.lang.RuntimeException: Unable to start activity ComponentInfo{tabs.app/tabs.app.Areas}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list' 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2242) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:631) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost.setCurrentTab(TabHost.java:317) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:127) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:346) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.performClick(View.java:2344) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.onTouchEvent(View.java:4133) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.View.dispatchTouchEvent(View.java:3672) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:850) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1712) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1202) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Activity.dispatchTouchEvent(Activity.java:1987) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1696) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.view.ViewRoot.handleMessage(ViewRoot.java:1658) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.os.Handler.dispatchMessage(Handler.java:99) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.os.Looper.loop(Looper.java:123) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.main(ActivityThread.java:4203) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at java.lang.reflect.Method.invokeNative(Native Method) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at java.lang.reflect.Method.invoke(Method.java:521) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at dalvik.system.NativeStart.main(Native Method) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list' 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ListActivity.onContentChanged(ListActivity.java:236) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:316) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Activity.setContentView(Activity.java:1620) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at tabs.app.Areas.onCreate(Areas.java:18) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364) 06-07 09:51:56.559: ERROR/AndroidRuntime(2034): ... 30 more 06-07 09:51:56.619: INFO/Process(51): Sending signal. PID: 2034 SIG: 3 06-07 09:51:56.619: INFO/dalvikvm(2034): threadid=7: reacting to signal 3 06-07 09:51:56.619: ERROR/dalvikvm(2034): Unable to open stack trace file '/data/anr/traces.txt': Permission denied Can someone please tell me what I'm doing wrong? Help greatly appreciated!

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  • MVC4 Model in View has nested data - cannot get data in model

    - by Taersious
    I have a Model defined that gets me a View with a list of RadioButtons, per IEnumerable. Within that Model, I want to display a list of checkboxes that will vary based on the item selected. Finally, there will be a Textarea in the same view once the user has selected from the available checkboxes, with some dynamic text there based on the CheckBoxes that are selected. What we should end up with is a Table-per-hierarchy. The layout is such that the RadioButtonList is in the first table cell, the CheckBoxList is in the middle table cell, and the Textarea is ini the right table cell. If anyone can guide me to what my model-view should be to achieve this result, I'll be most pleased... Here are my codes: // // View Model for implementing radio button list public class RadioButtonViewModel { // objects public List<RadioButtonItem> RadioButtonList { get; set; } public string SelectedRadioButton { get; set; } } // // Object for handling each radio button public class RadioButtonItem { // this object public string Name { get; set; } public bool Selected { get; set; } public int ObjectId { get; set; } // columns public virtual IEnumerable<CheckBoxItem> CheckBoxItems { get; set; } } // // Object for handling each checkbox public class CheckBoxViewModel { public List<CheckBoxItem> CheckBoxList { get; set; } } // // Object for handling each check box public class CheckBoxItem { public string Name { get; set; } public bool Selected { get; set; } public int ObjectId { get; set; } public virtual RadioButtonItem RadioButtonItem { get; set; } } and the view @model IEnumerable<EF_Utility.Models.RadioButtonItem> @{ ViewBag.Title = "Connect"; ViewBag.Selected = Request["name"] != null ? Request["name"].ToString() : ""; } @using (Html.BeginForm("Objects" , "Home", FormMethod.Post) ){ @Html.ValidationSummary(true) <table> <tbody> <tr> <td style="border: 1px solid grey; vertical-align:top;"> <table> <tbody> <tr> <th style="text-align:left; width: 50px;">Select</th> <th style="text-align:left;">View or Table Name</th> </tr> @{ foreach (EF_Utility.Models.RadioButtonItem item in @Model ) { <tr> <td> @Html.RadioButton("RadioButtonViewModel.SelectedRadioButton", item.Name, ViewBag.Selected == item.Name ? true : item.Selected, new { @onclick = "this.form.action='/Home/Connect?name=" + item.Name + "'; this.form.submit(); " }) </td> <td> @Html.DisplayFor(i => item.Name) </td> </tr> } } </tbody> </table> </td> <td style="border: 1px solid grey; width: 220px; vertical-align:top; @(ViewBag.Selected == "" ? "display:none;" : "")"> <table> <tbody> <tr> <th>Column </th> </tr> <tr> <td><!-- checkboxes will go here --> </td> </tr> </tbody> </table> </td> <td style="border: 1px solid grey; vertical-align:top; @(ViewBag.Selected == "" ? "display:none;" : "")"> <textarea name="output" id="output" rows="24" cols="48"></textarea> </td> </tr> </tbody> </table> } and the relevant controller public ActionResult Connect() { /* TEST SESSION FIRST*/ if( Session["connstr"] == null) return RedirectToAction("Index"); else { ViewBag.Message = ""; ViewBag.ConnectionString = Server.UrlDecode( Session["connstr"].ToString() ); ViewBag.Server = ParseConnectionString( ViewBag.ConnectionString, "Data Source" ); ViewBag.Database = ParseConnectionString( ViewBag.ConnectionString, "Initial Catalog" ); using( var db = new SysDbContext(ViewBag.ConnectionString)) { var objects = db.Set<SqlObject>().ToArray(); var model = objects .Select( o => new RadioButtonItem { Name = o.Name, Selected = false, ObjectId = o.Object_Id, CheckBoxItems = Enumerable.Empty<EF_Utility.Models.CheckBoxItem>() } ) .OrderBy( rb => rb.Name ); return View( model ); } } } What I am missing it seems, is the code in my Connect() method that will bring the data context forward; at that point, it should be fairly straight-forward to set up the Html for the View. EDIT ** So I am going to need to bind the RadioButtonItem to the view with something like the following, except my CheckBoxList will NOT be an empty set. // // POST: /Home/Connect/ [HttpPost] public ActionResult Connect( RadioButtonItem rbl ) { /* TEST SESSION FIRST*/ if ( Session["connstr"] == null ) return RedirectToAction( "Index" ); else { ViewBag.Message = ""; ViewBag.ConnectionString = Server.UrlDecode( Session["connstr"].ToString() ); ViewBag.Server = ParseConnectionString( ViewBag.ConnectionString, "Data Source" ); ViewBag.Database = ParseConnectionString( ViewBag.ConnectionString, "Initial Catalog" ); using ( var db = new SysDbContext( ViewBag.ConnectionString ) ) { var objects = db.Set<SqlObject>().ToArray(); var model = objects .Select( o => new RadioButtonItem { Name = o.Name, Selected = false, ObjectId = o.Object_Id, CheckBoxItems = Enumerable.Empty<EF_Utility.Models.CheckBoxItem>() } ) .OrderBy( rb => rb.Name ); return View( model ); } } }

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  • Unexpected ArrayIndexOutOfBoundsException in JavaFX application, refering to no array

    - by Eugene
    I have the following code: public void setContent(Importer3D importer) { if (DEBUG) { System.out.println("Initialization of Mesh's arrays"); } coords = importer.getCoords(); texCoords = importer.getTexCoords(); faces = importer.getFaces(); if (DEBUG) { System.out.println("Applying Mesh's arrays"); } mesh = new TriangleMesh(); mesh.getPoints().setAll(coords); mesh.getTexCoords().setAll(texCoords); mesh.getFaces().setAll(faces); if (DEBUG) { System.out.println("Initialization of the material"); } initMaterial(); if (DEBUG) { System.out.println("Setting the MeshView"); } meshView.setMesh(mesh); meshView.setMaterial(material); meshView.setDrawMode(DrawMode.FILL); if (DEBUG) { System.out.println("Adding to 3D scene"); } root3d.getChildren().clear(); root3d.getChildren().add(meshView); if (DEBUG) { System.out.println("3D model is ready!"); } } The Imporeter3D class part: private void load(File file) { stlLoader = new STLLoader(file); } public float[] getCoords() { return stlLoader.getCoords(); } public float[] getTexCoords() { return stlLoader.getTexCoords(); } public int[] getFaces() { return stlLoader.getFaces(); } The STLLoader: public class STLLoader{ public STLLoader(File file) { stlFile = new STLFile(file); loadManager = stlFile.loadManager; pointsArray = new PointsArray(stlFile); texCoordsArray = new TexCoordsArray(); } public float[] getCoords() { return pointsArray.getPoints(); } public float[] getTexCoords() { return texCoordsArray.getTexCoords(); } public int[] getFaces() { return pointsArray.getFaces(); } private STLFile stlFile; private PointsArray pointsArray; private TexCoordsArray texCoordsArray; private FacesArray facesArray; public SimpleBooleanProperty finished = new SimpleBooleanProperty(false); public LoadManager loadManager;} PointsArray file: public class PointsArray { public PointsArray(STLFile stlFile) { this.stlFile = stlFile; initPoints(); } private void initPoints() { ArrayList<Double> pointsList = stlFile.getPoints(); ArrayList<Double> uPointsList = new ArrayList<>(); faces = new int[pointsList.size()*2]; int n = 0; for (Double d : pointsList) { if (uPointsList.indexOf(d) == -1) { uPointsList.add(d); } faces[n] = uPointsList.indexOf(d); faces[++n] = 0; n++; } int i = 0; points = new float[uPointsList.size()]; for (Double d : uPointsList) { points[i] = d.floatValue(); i++; } } public float[] getPoints() { return points; } public int[] getFaces() { return faces; } private float[] points; private int[] faces; private STLFile stlFile; public static boolean DEBUG = true; } And STLFile: ArrayList<Double> coords = new ArrayList<>(); double temp; private void readV(STLParser parser) { for (int n = 0; n < 3; n++) { if(!(parser.ttype==STLParser.TT_WORD && parser.sval.equals("vertex"))) { System.err.println("Format Error:expecting 'vertex' on line " + parser.lineno()); } else { if (parser.getNumber()) { temp = parser.nval; coords.add(temp); if(DEBUG) { System.out.println("Vertex:"); System.out.print("X=" + temp + " "); } if (parser.getNumber()) { temp = parser.nval; coords.add(temp); if(DEBUG) { System.out.print("Y=" + temp + " "); } if (parser.getNumber()) { temp = parser.nval; coords.add(temp); if(DEBUG) { System.out.println("Z=" + temp + " "); } readEOL(parser); } else System.err.println("Format Error: expecting coordinate on line " + parser.lineno()); } else System.err.println("Format Error: expecting coordinate on line " + parser.lineno()); } else System.err.println("Format Error: expecting coordinate on line " + parser.lineno()); } if (n < 2) { try { parser.nextToken(); } catch (IOException e) { System.err.println("IO Error on line " + parser.lineno() + ": " + e.getMessage()); } } } } public ArrayList<Double> getPoints() { return coords; } As a result of all of this code, I expected to get 3d model in MeshView. But the present result is very strange: everything works and in DEBUG mode I get 3d model is ready! from setContent(), and then unexpected ArrayIndexOutOfBoundsException: File readed Initialization of Mesh's arrays Applying Mesh's arrays Initialization of the material Setting the MeshView Adding to 3D scene 3D model is ready! java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 32252 at com.sun.javafx.collections.ObservableFloatArrayImpl.rangeCheck(ObservableFloatArrayImpl.java:276) at com.sun.javafx.collections.ObservableFloatArrayImpl.get(ObservableFloatArrayImpl.java:184) at javafx.scene.shape.TriangleMesh.computeBounds(TriangleMesh.java:262) at javafx.scene.shape.MeshView.impl_computeGeomBounds(MeshView.java:151) at javafx.scene.Node.updateGeomBounds(Node.java:3497) at javafx.scene.Node.getGeomBounds(Node.java:3450) at javafx.scene.Node.getLocalBounds(Node.java:3432) at javafx.scene.Node.updateTxBounds(Node.java:3510) at javafx.scene.Node.getTransformedBounds(Node.java:3350) at javafx.scene.Node.updateBounds(Node.java:516) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.SubScene.updateBounds(SubScene.java:556) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.Parent.updateBounds(Parent.java:1668) at javafx.scene.Scene$ScenePulseListener.pulse(Scene.java:2309) at com.sun.javafx.tk.Toolkit.firePulse(Toolkit.java:329) at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:479) at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:459) at com.sun.javafx.tk.quantum.QuantumToolkit$13.run(QuantumToolkit.java:326) at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95) at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39) at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:101) at java.lang.Thread.run(Thread.java:724) Exception in thread "JavaFX Application Thread" java.lang.ArrayIndexOutOfBoundsException: Array index out of range: 32252 at com.sun.javafx.collections.ObservableFloatArrayImpl.rangeCheck(ObservableFloatArrayImpl.java:276) at com.sun.javafx.collections.ObservableFloatArrayImpl.get(ObservableFloatArrayImpl.java:184) The stranger thing is that this stack doesn't stop until I close the program. And moreover it doesn't point to any my array. What is this? And why does it happen?

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  • LinqToSql: How can I create a projection to adhere to DRY?

    - by mhutter
    Just wondering if there is a way to take some of the repitition out of a LINQ to SQL projected type. Example: Table: Address Fields: AddressID, HouseNumber, Street, City, State, Zip, +20 more Class MyAddress: AddressID, HouseNumber, Street (Only 3 fields) LINQ: from a in db.Addresses select new MyAddress { AddressID = a.AddressID, HouseNumber = a.HouseNumber, Street = a.Street } The above query works perfectly, and I understand why something like this will return all 20+ fields in each row: from a in db.Addresses select new MyAddress(a); class MyAddress { public MyAddress(Address a) { this.AddressID = a.AddressID, this.HouseNumber = a.HouseNumber, this.Street = a.Street } } Which leads me to my Question: Is it possible to implement some kind of helper function or extension method to "map" from the LINQ model to MyAddress yet only return the necessary fields in the query result rather than all of the fields?

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  • Lookup function not working (RS SP2)

    - by Al Reyes
    Hi, I made the upgrade to SP2. I'm trying to use the Lookup function to link data from two different servers. I'm trying first a simple exercise linking data from two datasets from the same server, having one dataset with journals and the other with the account description. My Expression looks like this at a field on the table I have: =Lookup(Fields!ACTINDX.Value,Fields!ACTINDX.Value,Fields!ACTDESCR.Value,"ACCTINFO") I made sure of the names and using only uppercases for datasets and fields but I'm receiving the following message when I try to preview: "An error occurred during local report processing. The definition of the report '/DETAIL' is invalid. The Value expression for the text box 'ACTINDX' refers to the field 'ACTDESCR'. Report item expressions can only refer to fields within the current dataset scope or, if inside an aggregate, the specified dataset scope". I'll appreciate any suggestions. Regards, Al

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  • jQuery event binding does not work properly or i can't make it properly working

    - by Saiful
    HTML: <input id="email" name="email" type=text /> <input id="password name="password" type="password" /> JavaScript: var fields = ["email","password"]; for (var i in fields) { var field = $("#"+fields[i]); field.bind({ focus: function() { field.css("border-color","#f00"); }, blur: function() { field.css("border-color","#000"); } }); } My desire action will be as follows: When I place cursor on any of the above fields the input field's border will be red. When I take away the cursor from the field it's border will be black. But the event is occurs only for the password filed whether I place and take away cursor form any of the above fields.

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  • Stop an input field in a form from being submitted

    - by Acorn
    I'm writing some javascript that will insert some input fields into a form on a website. The thing is, I don't want those input fields to affect the form in any way, I don't want them to be submitted when the form is submitted, I only want my javascript to have access to their values. Is there some way I could add some input fields into the middle of a form and not have them submitted when the form is submitted? Obviously the ideal thing would be for the input fields to not be in the form element, but I want the layout of my resulting page to have my inserted input fields appear between elements of the original form.

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  • Mysql database structure...

    - by Patrick
    I'm creating a members site, and I'm currently working on the user Preference settings. Should I create a table with all the preference fields (about 17 fields) or should I include them in the main member table along with the account settings? Is there a limit as to how many fields I should have in a table? currently the member table has about 21 fields... not sure if its okay to add another 17 more fields when I can easily just put them in another table. It'll take more coding to pull up the data though... any sugguestions?

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  • Should user preferences be included in the users table?

    - by Patrick
    I'm creating a members site, and I'm currently working on the user Preference settings. Should I create a table with all the preference fields (about 17 fields) or should I include them in the main member table along with the account settings? Is there a limit as to how many fields I should have in a table? currently the member table has about 21 fields... not sure if its okay to add another 17 more fields when I can easily just put them in another table. It'll take more coding to pull up the data though... any sugguestions?

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  • IBM PS/2 Keyboard with OS X 10.6 and PS2->USB Converter

    - by public static void
    Just got a new Mac Pro at work and as I can't stand the ZX Spectrum-esque 'dead flies' feel of the new Apple keyboards, I brought my trusty IBM SpaceSaver II to the office (with a USB/PS2 adapter) All seems generally to work ok - even the Trackpoint 'nipple' but periodically the modifier keys, notably the Ctrl and Windows keys seem to go into 'sticky' mode so that typing an 'S' brings up the save dialog, 'O' = open dialog etc. etc. Its generally fixed by switching windows and then returning back to the offending one, but this is really beginning to cheese me off. Can anyone suggest a fix?

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  • Using LINQ Distinct: With an Example on ASP.NET MVC SelectListItem

    - by Joe Mayo
    One of the things that might be surprising in the LINQ Distinct standard query operator is that it doesn’t automatically work properly on custom classes. There are reasons for this, which I’ll explain shortly. The example I’ll use in this post focuses on pulling a unique list of names to load into a drop-down list. I’ll explain the sample application, show you typical first shot at Distinct, explain why it won’t work as you expect, and then demonstrate a solution to make Distinct work with any custom class. The technologies I’m using are  LINQ to Twitter, LINQ to Objects, Telerik Extensions for ASP.NET MVC, ASP.NET MVC 2, and Visual Studio 2010. The function of the example program is to show a list of people that I follow.  In Twitter API vernacular, these people are called “Friends”; though I’ve never met most of them in real life. This is part of the ubiquitous language of social networking, and Twitter in particular, so you’ll see my objects named accordingly. Where Distinct comes into play is because I want to have a drop-down list with the names of the friends appearing in the list. Some friends are quite verbose, which means I can’t just extract names from each tweet and populate the drop-down; otherwise, I would end up with many duplicate names. Therefore, Distinct is the appropriate operator to eliminate the extra entries from my friends who tend to be enthusiastic tweeters. The sample doesn’t do anything with the drop-down list and I leave that up to imagination for what it’s practical purpose could be; perhaps a filter for the list if I only want to see a certain person’s tweets or maybe a quick list that I plan to combine with a TextBox and Button to reply to a friend. When the program runs, you’ll need to authenticate with Twitter, because I’m using OAuth (DotNetOpenAuth), for authentication, and then you’ll see the drop-down list of names above the grid with the most recent tweets from friends. Here’s what the application looks like when it runs: As you can see, there is a drop-down list above the grid. The drop-down list is where most of the focus of this article will be. There is some description of the code before we talk about the Distinct operator, but we’ll get there soon. This is an ASP.NET MVC2 application, written with VS 2010. Here’s the View that produces this screen: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<TwitterFriendsViewModel>" %> <%@ Import Namespace="DistinctSelectList.Models" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">     Home Page </asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">     <fieldset>         <legend>Twitter Friends</legend>         <div>             <%= Html.DropDownListFor(                     twendVM => twendVM.FriendNames,                     Model.FriendNames,                     "<All Friends>") %>         </div>         <div>             <% Html.Telerik().Grid<TweetViewModel>(Model.Tweets)                    .Name("TwitterFriendsGrid")                    .Columns(cols =>                     {                         cols.Template(col =>                             { %>                                 <img src="<%= col.ImageUrl %>"                                      alt="<%= col.ScreenName %>" />                         <% });                         cols.Bound(col => col.ScreenName);                         cols.Bound(col => col.Tweet);                     })                    .Render(); %>         </div>     </fieldset> </asp:Content> As shown above, the Grid is from Telerik’s Extensions for ASP.NET MVC. The first column is a template that renders the user’s Avatar from a URL provided by the Twitter query. Both the Grid and DropDownListFor display properties that are collections from a TwitterFriendsViewModel class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { /// /// For finding friend info on screen /// public class TwitterFriendsViewModel { /// /// Display names of friends in drop-down list /// public List FriendNames { get; set; } /// /// Display tweets in grid /// public List Tweets { get; set; } } } I created the TwitterFreindsViewModel. The two Lists are what the View consumes to populate the DropDownListFor and Grid. Notice that FriendNames is a List of SelectListItem, which is an MVC class. Another custom class I created is the TweetViewModel (the type of the Tweets List), shown below: namespace DistinctSelectList.Models { /// /// Info on friend tweets /// public class TweetViewModel { /// /// User's avatar /// public string ImageUrl { get; set; } /// /// User's Twitter name /// public string ScreenName { get; set; } /// /// Text containing user's tweet /// public string Tweet { get; set; } } } The initial Twitter query returns much more information than we need for our purposes and this a special class for displaying info in the View.  Now you know about the View and how it’s constructed. Let’s look at the controller next. The controller for this demo performs authentication, data retrieval, data manipulation, and view selection. I’ll skip the description of the authentication because it’s a normal part of using OAuth with LINQ to Twitter. Instead, we’ll drill down and focus on the Distinct operator. However, I’ll show you the entire controller, below,  so that you can see how it all fits together: using System.Linq; using System.Web.Mvc; using DistinctSelectList.Models; using LinqToTwitter; namespace DistinctSelectList.Controllers { [HandleError] public class HomeController : Controller { private MvcOAuthAuthorization auth; private TwitterContext twitterCtx; /// /// Display a list of friends current tweets /// /// public ActionResult Index() { auth = new MvcOAuthAuthorization(InMemoryTokenManager.Instance, InMemoryTokenManager.AccessToken); string accessToken = auth.CompleteAuthorize(); if (accessToken != null) { InMemoryTokenManager.AccessToken = accessToken; } if (auth.CachedCredentialsAvailable) { auth.SignOn(); } else { return auth.BeginAuthorize(); } twitterCtx = new TwitterContext(auth); var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); var twendsVM = new TwitterFriendsViewModel { Tweets = friendTweets, FriendNames = friendNames }; return View(twendsVM); } public ActionResult About() { return View(); } } } The important part of the listing above are the LINQ to Twitter queries for friendTweets and friendNames. Both of these results are used in the subsequent population of the twendsVM instance that is passed to the view. Let’s dissect these two statements for clarification and focus on what is happening with Distinct. The query for friendTweets gets a list of the 20 most recent tweets (as specified by the Twitter API for friend queries) and performs a projection into the custom TweetViewModel class, repeated below for your convenience: var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); The LINQ to Twitter query above simplifies what we need to work with in the View and the reduces the amount of information we have to look at in subsequent queries. Given the friendTweets above, the next query performs another projection into an MVC SelectListItem, which is required for binding to the DropDownList.  This brings us to the focus of this blog post, writing a correct query that uses the Distinct operator. The query below uses LINQ to Objects, querying the friendTweets collection to get friendNames: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); The above implementation of Distinct seems normal, but it is deceptively incorrect. After running the query above, by executing the application, you’ll notice that the drop-down list contains many duplicates.  This will send you back to the code scratching your head, but there’s a reason why this happens. To understand the problem, we must examine how Distinct works in LINQ to Objects. Distinct has two overloads: one without parameters, as shown above, and another that takes a parameter of type IEqualityComparer<T>.  In the case above, no parameters, Distinct will call EqualityComparer<T>.Default behind the scenes to make comparisons as it iterates through the list. You don’t have problems with the built-in types, such as string, int, DateTime, etc, because they all implement IEquatable<T>. However, many .NET Framework classes, such as SelectListItem, don’t implement IEquatable<T>. So, what happens is that EqualityComparer<T>.Default results in a call to Object.Equals, which performs reference equality on reference type objects.  You don’t have this problem with value types because the default implementation of Object.Equals is bitwise equality. However, most of your projections that use Distinct are on classes, just like the SelectListItem used in this demo application. So, the reason why Distinct didn’t produce the results we wanted was because we used a type that doesn’t define its own equality and Distinct used the default reference equality. This resulted in all objects being included in the results because they are all separate instances in memory with unique references. As you might have guessed, the solution to the problem is to use the second overload of Distinct that accepts an IEqualityComparer<T> instance. If you were projecting into your own custom type, you could make that type implement IEqualityComparer<T>, but SelectListItem belongs to the .NET Framework Class Library.  Therefore, the solution is to create a custom type to implement IEqualityComparer<T>, as in the SelectListItemComparer class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { public class SelectListItemComparer : EqualityComparer { public override bool Equals(SelectListItem x, SelectListItem y) { return x.Value.Equals(y.Value); } public override int GetHashCode(SelectListItem obj) { return obj.Value.GetHashCode(); } } } The SelectListItemComparer class above doesn’t implement IEqualityComparer<SelectListItem>, but rather derives from EqualityComparer<SelectListItem>. Microsoft recommends this approach for consistency with the behavior of generic collection classes. However, if your custom type already derives from a base class, go ahead and implement IEqualityComparer<T>, which will still work. EqualityComparer is an abstract class, that implements IEqualityComparer<T> with Equals and GetHashCode abstract methods. For the purposes of this application, the SelectListItem.Value property is sufficient to determine if two items are equal.   Since SelectListItem.Value is type string, the code delegates equality to the string class. The code also delegates the GetHashCode operation to the string class.You might have other criteria in your own object and would need to define what it means for your object to be equal. Now that we have an IEqualityComparer<SelectListItem>, let’s fix the problem. The code below modifies the query where we want distinct values: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct(new SelectListItemComparer()) .ToList(); Notice how the code above passes a new instance of SelectListItemComparer as the parameter to the Distinct operator. Now, when you run the application, the drop-down list will behave as you expect, showing only a unique set of names. In addition to Distinct, other LINQ Standard Query Operators have overloads that accept IEqualityComparer<T>’s, You can use the same techniques as shown here, with SelectListItemComparer, with those other operators as well. Now you know how to resolve problems with getting Distinct to work properly and also have a way to fix problems with other operators that require equality comparisons. @JoeMayo

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  • C#/.NET Little Wonders: The EventHandler and EventHandler&lt;TEventArgs&gt; delegates

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the last two weeks, we examined the Action family of delegates (and delegates in general), and the Func family of delegates and how they can be used to support generic, reusable algorithms and classes. So this week, we are going to look at a handy pair of delegates that can be used to eliminate the need for defining custom delegates when creating events: the EventHandler and EventHandler<TEventArgs> delegates. Events and delegates Before we begin, let’s quickly consider events in .NET.  According to the MSDN: An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. So, basically, you can create an event in a type so that users of that type can subscribe to notifications of things of interest.  How is this different than some of the delegate programming that we talked about in the last two weeks?  Well, you can think of an event as a special access modifier on a delegate.  Some differences between the two are: Events are a special access case of delegates They behave much like delegates instances inside the type they are declared in, but outside of that type they can only be (un)subscribed to. Events can specify add/remove behavior explicitly If you want to do additional work when someone subscribes or unsubscribes to an event, you can specify the add and remove actions explicitly. Events have access modifiers, but these only specify the access level of those who can (un)subscribe A public event, for example, means anyone can (un)subscribe, but it does not mean that anyone can raise (invoke) the event directly.  Events can only be raised by the type that contains them In contrast, if a delegate is visible, it can be invoked outside of the object (not even in a sub-class!). Events tend to be for notifications only, and should be treated as optional Semantically speaking, events typically don’t perform work on the the class directly, but tend to just notify subscribers when something of note occurs. My basic rule-of-thumb is that if you are just wanting to notify any listeners (who may or may not care) that something has happened, use an event.  However, if you want the caller to provide some function to perform to direct the class about how it should perform work, make it a delegate. Declaring events using custom delegates To declare an event in a type, we simply use the event keyword and specify its delegate type.  For example, let’s say you wanted to create a new TimeOfDayTimer that triggers at a given time of the day (as opposed to on an interval).  We could write something like this: 1: public delegate void TimeOfDayHandler(object source, ElapsedEventArgs e); 2:  3: // A timer that will fire at time of day each day. 4: public class TimeOfDayTimer : IDisposable 5: { 6: // Event that is triggered at time of day. 7: public event TimeOfDayHandler Elapsed; 8:  9: // ... 10: } The first thing to note is that the event is a delegate type, which tells us what types of methods may subscribe to it.  The second thing to note is the signature of the event handler delegate, according to the MSDN: The standard signature of an event handler delegate defines a method that does not return a value, whose first parameter is of type Object and refers to the instance that raises the event, and whose second parameter is derived from type EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. So, in a nutshell, the event handler delegates should return void and take two parameters: An object reference to the object that raised the event. An EventArgs (or a subclass of EventArgs) reference to event specific information. Even if your event has no additional information to provide, you are still expected to provide an EventArgs instance.  In this case, feel free to pass the EventArgs.Empty singleton instead of creating new instances of EventArgs (to avoid generating unneeded memory garbage). The EventHandler delegate Because many events have no additional information to pass, and thus do not require custom EventArgs, the signature of the delegates for subscribing to these events is typically: 1: // always takes an object and an EventArgs reference 2: public delegate void EventHandler(object sender, EventArgs e) It would be insane to recreate this delegate for every class that had a basic event with no additional event data, so there already exists a delegate for you called EventHandler that has this very definition!  Feel free to use it to define any events which supply no additional event information: 1: public class Cache 2: { 3: // event that is raised whenever the cache performs a cleanup 4: public event EventHandler OnCleanup; 5:  6: // ... 7: } This will handle any event with the standard EventArgs (no additional information).  But what of events that do need to supply additional information?  Does that mean we’re out of luck for subclasses of EventArgs?  That’s where the generic for of EventHandler comes into play… The generic EventHandler<TEventArgs> delegate Starting with the introduction of generics in .NET 2.0, we have a generic delegate called EventHandler<TEventArgs>.  Its signature is as follows: 1: public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e) 2: where TEventArgs : EventArgs This is similar to EventHandler except it has been made generic to support the more general case.  Thus, it will work for any delegate where the first argument is an object (the sender) and the second argument is a class derived from EventArgs (the event data). For example, let’s say we wanted to create a message receiver, and we wanted it to have a few events such as OnConnected that will tell us when a connection is established (probably with no additional information) and OnMessageReceived that will tell us when a new message arrives (probably with a string for the new message text). So for OnMessageReceived, our MessageReceivedEventArgs might look like this: 1: public sealed class MessageReceivedEventArgs : EventArgs 2: { 3: public string Message { get; set; } 4: } And since OnConnected needs no event argument type defined, our class might look something like this: 1: public class MessageReceiver 2: { 3: // event that is called when the receiver connects with sender 4: public event EventHandler OnConnected; 5:  6: // event that is called when a new message is received. 7: public event EventHandler<MessageReceivedEventArgs> OnMessageReceived; 8:  9: // ... 10: } Notice, nowhere did we have to define a delegate to fit our event definition, the EventHandler and generic EventHandler<TEventArgs> delegates fit almost anything we’d need to do with events. Sidebar: Thread-safety and raising an event When the time comes to raise an event, we should always check to make sure there are subscribers, and then only raise the event if anyone is subscribed.  This is important because if no one is subscribed to the event, then the instance will be null and we will get a NullReferenceException if we attempt to raise the event. 1: // This protects against NullReferenceException... or does it? 2: if (OnMessageReceived != null) 3: { 4: OnMessageReceived(this, new MessageReceivedEventArgs(aMessage)); 5: } The above code seems to handle the null reference if no one is subscribed, but there’s a problem if this is being used in multi-threaded environments.  For example, assume we have thread A which is about to raise the event, and it checks and clears the null check and is about to raise the event.  However, before it can do that thread B unsubscribes to the event, which sets the delegate to null.  Now, when thread A attempts to raise the event, this causes the NullReferenceException that we were hoping to avoid! To counter this, the simplest best-practice method is to copy the event (just a multicast delegate) to a temporary local variable just before we raise it.  Since we are inside the class where this event is being raised, we can copy it to a local variable like this, and it will protect us from multi-threading since multicast delegates are immutable and assignments are atomic: 1: // always make copy of the event multi-cast delegate before checking 2: // for null to avoid race-condition between the null-check and raising it. 3: var handler = OnMessageReceived; 4: 5: if (handler != null) 6: { 7: handler(this, new MessageReceivedEventArgs(aMessage)); 8: } The very slight trade-off is that it’s possible a class may get an event after it unsubscribes in a multi-threaded environment, but this is a small risk and classes should be prepared for this possibility anyway.  For a more detailed discussion on this, check out this excellent Eric Lippert blog post on Events and Races. Summary Generic delegates give us a lot of power to make generic algorithms and classes, and the EventHandler delegate family gives us the flexibility to create events easily, without needing to redefine delegates over and over.  Use them whenever you need to define events with or without specialized EventArgs.   Tweet Technorati Tags: .NET, C#, CSharp, Little Wonders, Generics, Delegates, EventHandler

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