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  • A Null Reference Exception

    - by Alex
    "Object reference not set to an instance of an object." using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.Graphics; namespace XNAdev { class Sprite { //The size of the Sprite public Rectangle Size; //Used to size the Sprite up or down from the original image public float Scale = 1.0f; //The current position of the Sprite public Vector2 Position = new Vector2(115, 0); //The texture object used when drawing the sprite private Texture2D mSpriteTexture; //Load the texture for the sprite using the Content Pipeline public void LoadContent(ContentManager theContentManager, string theAssetName) { mSpriteTexture = theContentManager.Load<Texture2D>(theAssetName); Size = new Rectangle(0, 0, (int)(mSpriteTexture.Width * Scale), (int)(mSpriteTexture.Height * Scale)); } //Draw the sprite to the screen public void Draw(SpriteBatch theSpriteBatch) { theSpriteBatch.Draw(mSpriteTexture, Position, new Rectangle(0, 0, mSpriteTexture.Width, mSpriteTexture.Height), Color.White, 0.0f, Vector2.Zero, Scale, SpriteEffects.None, 0); } } } I am very new at this C# so any help would be great. I have no idea what my error is.

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  • Statically Init a derived class

    - by AC
    With c++, Is there a way to get a derived class to inherit its own static initializer? I am trying to do something like the following: class Base { public: class StaticInit { public: virtual StaticInit() =0; }; }; class Derived: public Base { public: virtual StaticInit::StaticInit() { //do something with the derived class } static StaticInit init; } static Derived::StaticInit init; it would also be nice if I didn't have to define the init var in each derived class. I am currently redefining the StaticInit internal class in each derived class but it seems redundant. Each derived class is a singleton, and I need the instance to be stored in a lookup table at program startup.

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  • C# specifying generic delegate type param at runtime

    - by smerlin
    following setup, i have several generic functions, and i need to choose the type and the function identified by two strings at runtime. my first try looked like this: public static class FOOBAR { public delegate void MyDelegateType(int param); public static void foo<T>(int param){...} public static void bar<T>(int param){...} public static void someMethod(string methodstr, string typestr) { MyDelegateType mydel; Type mytype; switch(typestr) { case "int": mytype = typeof(int); break; case "double": mytype = typeof(double); break; default: throw new InvalidTypeException(typestr); } switch(methodstr) { case "foo": mydel = foo<mytype>; //error break; case "bar": mydel = bar<mytype>; //error break; default: throw new InvalidTypeException(methodstr); } for(int i=0; i<1000; ++i) mydel(i); } } since this didnt work, i nested those switchs (a methodstr switch inside the typestr switch or viceversa), but that solution is really ugly and unmaintainable. The number of types is pretty much fixed, but the number of functions like foo or bar will increase by high numbers, so i dont want nested switchs. So how can i make this working without using nested switchs ?

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  • How does ambigous methods are resolved in java ?

    - by Jijoy
    Hi , I do have a question. package org.study.algos; public class Study { public static void main(String[] args) { A a = new A(); a.m1(null); } } class A { public void m1(String s) { System.out.println("String"); System.out.println(s); } public void m1(Object obj) { System.out.println("Object"); System.out.println(obj); } } Here , the output is String null Why JVM resolve the method to one with String arguement ? Thanks in advance J

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  • Java Inheritance Concept Understanding

    - by Nirmal
    Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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  • multiple inheritance

    - by hitech
    when we say "a member declated as protected is accessible to any class imediately derived from it" what does this mean. in the follwing example get_number function can be accessible by the result class , as per the statement it sould only be accessile to test class. class student { protected: int roll_number; public: void get_number(int){ cout<< "hello"; } void put_number(void) {cout<< "hello"; } }; class test : public student { protected : float sub1; float sub2; public: void get_marks(float, float) {cout<< "hello"; roll_number = 10; } void put_marks(void) {cout<< "hello"; cout << "roll_number = " << roll_number ; } }; class result :public test { float total; public: void display(){cout<< "hello"; roll_number = 10; } }; int main() { result student; student.get_marks(2.2, 2.2); student.put_marks(); return 0; } i changed the code as per the first statement the protected variable roll_number not be accessible upto the result class ?

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  • What does this recursive function do?

    - by null
    What does this function do? And how do you evaluate it? How to trace it? How to understand recursive method? I just can't understand the recursion, and the exam date is coming soon, and I know in order to understand recursion, I must first understand recursion. But I just can't write a slightly complex recursive method, can anyone help me out using the simplest English words. public class BalancedStrings { public static void printBalanced(String prefix, int a, int b) { if (a > 0) printBalanced(prefix + "a", a - 1, b); if (b > 0) printBalanced(prefix + "b", a, b - 1); if (a == 0 && b == 0) System.out.println(prefix); } public static void printBalanced(int n) { if (n % 2 == 0) { printBalanced("", n / 2, n / 2); } } public static void main(String[] args) { printBalanced(4); } }

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  • Use nested static class as ActionListener for the Outer class

    - by Digvijay Yadav
    I want to use an nested static class as an actionListener for the enclosing class's GUI elements. I did something like this: public class OuterClass { public static void myImplementation() { OuterClass.StartupHandler startupHandler = new OuterClass.StartupHandler(); exitMenuItem.addActionListener(startupHandler); // error Line } public static class StartupHandler implements ActionListener { @Override public void actionPerformed(ActionEvent e) { //throw new UnsupportedOperationException("Not supported yet."); if (e.getSource() == exitMenuItem) { System.exit(1); } else if (e.getSource() == helpMenuItem) { // show help menu } } } } But when I invoke this code I get the NullPointerException at the //error Line. Is this the right method to do do this or there is something I did am missing?

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  • unix cut, remove first token

    - by Mike
    I'm trying to use unix cut to remove the first two fields per line. I have input lines of of the form (token)(whitespace)(token)(lots of text) The problem is that there exit n tokens per line, so I can't do something like this cut -f3,4,5,6,7,8,9 is there a way to tell cut to take everything except the specified fields

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  • what is serialization and how it works

    - by Rozer
    I know the serialization process but have't implemented it. In my application i have seen there are various classes that has been implemented serilizable interface. consider following class public class DBAccessRequest implements Serializable { private ActiveRequest request = null; private Connection connection = null; private static Log log = LogFactory.getLog(DBAccessRequest.class); public DBAccessRequest(ActiveRequest request,Connection connection) { this.request = request; this.connection = connection; } /** * @return Returns the DB Connection object. */ public Connection getConnection() { return connection; } /** * @return Returns the active request object for the db connection. */ public ActiveRequest getRequest() { return request; } } just setting request and connection in constructor and having getter setter for them. so what is the use of serilizable implementation over here...

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  • C#, Can I move dictionary initial code out from the constructor?

    - by 5YrsLaterDBA
    Here is my code right now. But I would like to move those "Add" out from the constructor. Can we initialize Dictionary when we new it? or you have another better idea. Basically I want to define few characters which are used in many places. public class User { public enum actionEnum { In, Out, Fail } public static Dictionary<actionEnum, String> loginAction = new Dictionary<actionEnum, string>(); public User() { loginAction.Add(actionEnum.In, "I"); loginAction.Add(actionEnum.Out, "O"); loginAction.Add(actionEnum.Fail, "F"); } ..... }

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  • NHibernate Entity code conversion from #C to VB.Net

    - by CoderRoller
    Hello and thanks for your help in advance. I am starting on the NHibernate world and i am experimenting with the NHibernate CookBook recipes, i am trying to set a base entity class for my entities and this is the C# code for this. I would like to know whats the VB.NET version so i can implement it in my sample project. This is the C# code: public abstract class Entity<TId> { public virtual TId Id { get; protected set; } public override bool Equals(object obj) { return Equals(obj as Entity<TId>); } private static bool IsTransient(Entity<TId> obj) { return obj != null && Equals(obj.Id, default(TId)); } private Type GetUnproxiedType() { return GetType(); } public virtual bool Equals(Entity<TId> other) { if (other == null) return false; if (ReferenceEquals(this, other)) return true; if (!IsTransient(this) && !IsTransient(other) && Equals(Id, other.Id)) { var otherType = other.GetUnproxiedType(); var thisType = GetUnproxiedType(); return thisType.IsAssignableFrom(otherType) || otherType.IsAssignableFrom(thisType); } return false; } public override int GetHashCode() { if (Equals(Id, default(TId))) return base.GetHashCode(); return Id.GetHashCode(); } } I tried using an online converter but puts a Nothing reference in place of default(TId) that doesn't seem right to me that's why I request for help: Private Shared Function IsTransient(obj As Entity(Of TId)) As Boolean Return obj IsNot Nothing AndAlso Equals(obj.Id, Nothing) End Function I Would appreciate the insight you may give me on the subject.

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  • Difference between Class Abstraction and Object Interfaces in PHP?

    - by Mark Tomlin
    What is the difference between a Class Abstraction and an Object Interfaces in PHP? I ask because, I don't really see the point to both of them, they both do the same thing! So, what are the advantages of disadvantages using both against one or the other? Class Abstraction: abstract class aClass { // Force extending class to define these methods abstract public function setVariable($name, $var); abstract public function getHtml($template); } Object Interface: interface iClass { // Force impementing class to define these methods public function setVariable($name, $var); public function getHtml($template); }

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  • Dictionary w/ null key?

    - by Ralph
    Firstly, why doesn't Dictionary<TKey, TValue> support a single null key? Secondly, is there an existing dictionary-like collection that does? I want to store an "empty" or "missing" or "default" System.Type, thought null would work well for this. More specifically, I've written this class: class Switch { private Dictionary<Type, Action<object>> _dict; public Switch(params KeyValuePair<Type, Action<object>>[] cases) { _dict = new Dictionary<Type, Action<object>>(cases.Length); foreach (var entry in cases) _dict.Add(entry.Key, entry.Value); } public void Execute(object obj) { var type = obj.GetType(); if (_dict.ContainsKey(type)) _dict[type](obj); } public static void Execute(object obj, params KeyValuePair<Type, Action<object>>[] cases) { var type = obj.GetType(); foreach (var entry in cases) { if (entry.Key == null || type.IsAssignableFrom(entry.Key)) { entry.Value(obj); break; } } } public static KeyValuePair<Type, Action<object>> Case<T>(Action action) { return new KeyValuePair<Type, Action<object>>(typeof(T), x => action()); } public static KeyValuePair<Type, Action<object>> Case<T>(Action<T> action) { return new KeyValuePair<Type, Action<object>>(typeof(T), x => action((T)x)); } public static KeyValuePair<Type, Action<object>> Default(Action action) { return new KeyValuePair<Type, Action<object>>(null, x => action()); } } For switching on types. There are two ways to use it: Statically. Just call Switch.Execute(yourObject, Switch.Case<YourType>(x => x.Action())) Precompiled. Create a switch, and then use it later with switchInstance.Execute(yourObject) Works great except when you try to add a default case to the "precompiled" version (null argument exception).

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  • Minor tweak to this javascript function?

    - by RKS
    I have a script that shows/hides used via onClick. I can get it to show/hide just fine, but I can't get it to show/'hide everything else'. So what I get is a bunch of open containers when I really want just the one. Javascript: <script> function showfields(fields){ if(document.getElementById(fields).style.display=='none'){ document.getElementById(fields).style.display='block'; } else{ document.getElementById(fields).style.display = 'none'; } } </script> HTML: <div id="hidden" class="steps" style="display: block;"> <div class="section" style="margin-right: 10px;"> <h2>Something</h2> </div> <button class="continue dropdown" id="showLink" onClick="showfields('hidden2');return false;" href="#">Continue</button> </div> <div id="hidden2" class="steps" style="display: block;"> <div class="section" style="margin-right: 10px;"> <h2>Something2</h2> </div> <button class="continue dropdown" id="showLink" onClick="showfields('hidden3');return false;" href="#">Continue</button> </div> <div id="hidden3" class="steps" style="display: block;"> <div class="section" style="margin-right: 10px;"> <h2>Something3</h2> </div> <button class="continue dropdown" id="showLink" onClick="showfields('hidden3');return false;" href="#">Continue</button> </div> <div id="hidden4" class="steps" style="display: block;"> <div class="section" style="margin-right: 10px;"> <h2>Something4</h2> </div> <button class="continue dropdown" id="showLink" onClick="showfields('hidden4');return false;" href="#">Continue</button> </div> Thanks

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  • Implementing a Version check between an Abstract class and it's implementation

    - by Michael Stum
    I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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  • Strange "cache" effect between client and server

    - by mark
    I use a Socket-based connection between Client and server with ObjectOutputStream. The objects serialized and exchanged have this structure: public class RichiestaSalvataggioArticolo implements Serializable { private ArticoloDati articolo; public RichiestaSalvataggioArticolo(ArticoloDati articolo) { this.articolo = articolo; } @Override public void ricevi(GestoreRichieste gestore) throws Exception { gestore.interpreta(this); } public ArticoloDati getArticolo() { return articolo; } } the issue is that when I try to exchange messages between C/S with incapsulated content very similar (ArticoloDati whom differ only in 2 fields out of 10), the Client sends an ArticoloDati, but the Server receives the previous one. Does the ObjectOutputStream implement some kind of cache or memory between the calls, that fails to recognize that my 2 objects are different because they are very similar?

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  • Passing object through WCF so that server receives client changes

    - by cvig
    I would like to set up a WCF service so that any changes a client makes to an object I send them are also reflected on the server side. For example, if Assembly A has the following... namespace AssemblyA { public class Person { public string FirstName { get; set; } public string LastName { get; set; } } [ServiceContract] public interface IServer { [OperationContract] Person GetPerson(); } } And Assembly B references Assembly A... using AssemblyA; namespace AssemblyB { class Program { static void Main(string[] args) { <snip> IServer server = factory.CreateChannel(); Person person = server.GetPerson(); person.FirstName = "Kilroy"; person.LastName = "WuzHere"; } } } What is the easiest/best way to make it so that the service's copy of the Person object also reflects the changes that the client makes? Is this even possible?

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  • PHP 5.3 and interface \ArrayAccess

    - by Jakub Lédl
    I'm now working on a project and I have one class that implements the ArrayAccess interface. Howewer, I'm getting an error that says that my implementation: must be compatible with that of ArrayAccess::offsetSet(). My implementation looks like this: public function offsetSet($offset, $value) { if (!is_string($offset)) { throw new \LogicException("..."); } $this->params[$offset] = $value; } So, to me it looks like my implementation is correct. Any idea what is wrong? Thanks very much! The class look like this: class HttpRequest implements \ArrayAccess { // tons of private variables, methods for working // with current http request etc. Really nothing that // could interfere with that interface. // ArrayAccess implementation public function offsetExists($offset) { return isset ($this->params[$offset]); } public function offsetGet($offset) { return isset ($this->params[$offset]) ? $this->params[$offset] : NULL; } public function offsetSet($offset, $value) { if (!is_string($offset)) { throw new \LogicException("You can only assing to params using specified key."); } $this->params[$offset] = $value; } public function offsetUnset($offset) { unset ($this->params[$offset]); } }

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  • Polymorphism and c#

    - by saurabh
    Here one more basic question asked in MS interview recently Class A { public virtual void Method1(){} public void Method2() { Method1(); } } class B:A { public override void Method1() { } } Class main { A obk = new B(); obk.Method2(); } now tell me which function gets called ? sorry for the typos.

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  • How we can dyanamically bind data with diffrerent dropdownlist in a grid view?

    - by Lock up
    i am wking on an assignment in which i have a gridview that contain deptno in a dropdownlist.by selecting a particular deptno from that dropdownlist,the number of employee of that department displayed in second dropdownlist that is for displaying employyee of a department.And after selecting the employee its salary detail and date of joining displayed in textboxes?we have two database table one is for employee(fields are deptno,empname,salary,joining date,status(true/false))and second department(fields are deptno,deptname,location);;;

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  • Unit test approach for generic classes/methods

    - by Greg
    Hi, What's the recommended way to cover off unit testing of generic classes/methods? For example (referring to my example code below). Would it be a case of have 2 or 3 times the tests to cover testing the methods with a few different types of TKey, TNode classes? Or is just one class enough? public class TopologyBase<TKey, TNode, TRelationship> where TNode : NodeBase<TKey>, new() where TRelationship : RelationshipBase<TKey>, new() { // Properties public Dictionary<TKey, NodeBase<TKey>> Nodes { get; private set; } public List<RelationshipBase<TKey>> Relationships { get; private set; } // Constructors protected TopologyBase() { Nodes = new Dictionary<TKey, NodeBase<TKey>>(); Relationships = new List<RelationshipBase<TKey>>(); } // Methods public TNode CreateNode(TKey key) { var node = new TNode {Key = key}; Nodes.Add(node.Key, node); return node; } public void CreateRelationship(NodeBase<TKey> parent, NodeBase<TKey> child) { . . .

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