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  • Attribute vector emptying itself

    - by ravloony
    Hello, I have two classes, derived from a common class. The common class has a pure virtual function called execute(), which is implemented in both derived classes. In the inherited class I have an attribute which is a vector. In both execute() methods I overwrite this vector with a result. I access both classes from a vector of pointers to their objects. The problem is when I try to access the result vector form outside the objects. In one case I can get the elements (which are simply pointers), in the other I cannot, the vector is empty. Code: class E; class A{ protected: vector<E*> _result; public: virtual void execute()=0; vector<E*> get_result(); }; vector<E*> A::get_result() { return _result; } class B : public A { public: virtual void execute(); }; B::execute() { //... _result = tempVec; return; } class C : public A { public: virtual void execute(); }; C::execute() { //different stuff to B _result = tempvec; return; } main() { B* b = new B(); C* c = new C(); b->execute(); c->execute(); b->get_result();//returns full vector c->get_result(); //returns empty vector!! } I have no idea what is going on here... I have tried filling _result by hand from a temp vector in the offending class, doing the same with vector::assign(), nothing works. And the other object works perfectly. I must be missing something.... Any help would be greatly appreciated.

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  • Not using Web Server for html pages

    - by Manoj
    For an intranet application instead of using a proper web server, it has been planned to just deploy static html pages by sharing it over the network. This static html page is continously updated in the background by a program running on that PC and people access this html page by typing the shared file path directly in the browser. A maximum of 10 simultaneous users are expected to access it. Can any one see the disadvantages or advantages in this type of deployment?

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  • Can I use an abstract class instead of a private __construct() when creating a singleton in PHP?

    - by Pheter
    When creating a Singleton in PHP, I ensure that it cannot be instantiated by doing the following: class Singleton { private function __construct() {} private function __clone() {} public static function getInstance() {} } However, I realised that defining a class as 'abstract' means that it cannot be instantiated. So is there anything wrong with doing the following instead: abstract class Singleton { public static function getInstance() {} } The second scenario allows me to write fewer lines of code which would be nice. (Not that it actually makes much of a difference.)

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  • Retain IEnumerable<T> value during postback

    - by ScG
    I have an IEnumerable< T which is declared on the page like this: IEnumerable< Person person; When the page postsback, the person list is null. How can I retain the values of person list without declaring it as static? Sr. devs in my company say that you should not declare the list as static.

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  • Crossthread exception and invokerequired solution doesn't change my control value

    - by Pilouk
    EDIT Solution : Here i'm setting my byref value in each object then i'm running a backgroundworker Private Sub TelechargeFichier() Dim DocManquant As Boolean = False Dim docName As String = "" Dim lg As String = "" Dim telechargementFini As Boolean = False lblMessage.Text = EasyDealChangeLanguage.Instance.GetStringFromResourceName("1478") prgBar.Maximum = m_listeFichiers.Count For i As Integer = 0 To m_listeFichiers.Count - 1 m_listeFichiers(i).Set_ByRefLabel(lblMessage) m_listeFichiers(i).Set_ByRefPrgbar(prgBar) m_listeThreads.Add(New Thread(AddressOf m_listeFichiers(i).DownloadMe)) Next m_bgWorker = New BackgroundWorker m_bgWorker.WorkerReportsProgress = True AddHandler m_bgWorker.DoWork, AddressOf DownloadFiles m_bgWorker.RunWorkerAsync() ''Completed 'lblMessage.Text = EasyDealChangeLanguage.Instance.GetStringFromResourceName("1383") 'Me.DialogResult = System.Windows.Forms.DialogResult.OK End Sub Here is my downloadFiles function : Note that each start will do the downloadMe function see below too Private Sub DownloadFiles(sender As Object, e As DoWorkEventArgs) For i As Integer = 0 To m_listeThreads.Count - 1 m_listeThreads(i).Start() Next For i As Integer = 0 To m_listeThreads.Count - 1 m_listeThreads(i).Join() Next End Sub I have multiple thread that each will download a ftp file. I would like that each file that have been completed will set a value to a progress bar and a label from my UI thread. For some reason invokerequired never change to false. Here is my little function that start all the thread Private Sub TelechargeFichier() Dim DocManquant As Boolean = False Dim docName As String = "" Dim lg As String = "" Dim telechargementFini As Boolean = False lblMessage.Text = EasyDealChangeLanguage.Instance.GetStringFromResourceName("1478") prgBar.Maximum = m_listeFichiers.Count For i As Integer = 0 To m_listeFichiers.Count - 1 m_listeFichiers(i).Set_ByRefLabel(lblMessage) m_listeFichiers(i).Set_ByRefPrgbar(prgBar) m_listeThreads.Add(New Thread(AddressOf m_listeFichiers(i).DownloadMe)) Next For i As Integer = 0 To m_listeThreads.Count - 1 m_listeThreads(i).Start() Next For i As Integer = 0 To m_listeThreads.Count - 1 m_listeThreads(i).Join() Next 'Completed lblMessage.Text = EasyDealChangeLanguage.Instance.GetStringFromResourceName("1383") Me.DialogResult = System.Windows.Forms.DialogResult.OK End Sub Here my property that hold the Byref control from the UI thread. This is in my object which content the addressof function that will download the file (DownloadMe) Public Sub Set_ByRefPrgbar(ByRef prgbar As ProgressBar) m_prgBar = prgbar End Sub Public Sub Set_ByRefLabel(ByRef lbl As EasyDeal.Controls.EasyDealLabel3D) m_lblMessage = lbl End Sub Here is the download function : Public Sub DownloadMe() Dim ftpReq As FtpWebRequest Dim ftpResp As FtpWebResponse = Nothing Dim streamInput As Stream Dim fileStreamOutput As FileStream Try ftpReq = CType(WebRequest.Create(EasyDeal.Controls.Common.FTP_CONNECTION & m_downloadFtpPath & m_filename), FtpWebRequest) ftpReq.Credentials = New NetworkCredential(FTP_USER, FTP_PASS) ftpReq.Method = WebRequestMethods.Ftp.DownloadFile ftpResp = ftpReq.GetResponse streamInput = ftpResp.GetResponseStream() fileStreamOutput = New FileStream(m_outputPath, FileMode.Create, FileAccess.ReadWrite) ReadWriteStream(streamInput, fileStreamOutput) Catch ex As Exception 'Au pire la fichier sera pas downloader Finally If ftpResp IsNot Nothing Then ftpResp.Close() End If Dim nomFichier As String = m_displaynameEN If EasyDealChangeLanguage.GetCurrentLanguageTypes = EasyDealChangeLanguage.EnumLanguageType.Francais Then nomFichier = m_displaynameFR End If If m_lblMessage IsNot Nothing Then EasyDealCommon.TH_SetControlText(m_lblMessage, String.Format(EasyDealChangeLanguage.Instance.GetStringFromResourceName("1479"), nomFichier)) End If If m_prgBar IsNot Nothing Then EasyDealCommon.TH_SetPrgValue(m_prgBar, 1) End If End Try End Sub Here is the crossthread invoke solution function : Public Sub TH_SetControlText(ByVal ctl As Control, ByVal text As String) If ctl.InvokeRequired Then ctl.BeginInvoke(New Action(Of Control, String)(AddressOf TH_SetControlText), ctl, text) Else ctl.Text = text End If End Sub Public Sub TH_SetPrgValue(ByVal prg As ProgressBar, ByVal value As Integer) If prg.InvokeRequired Then prg.BeginInvoke(New Action(Of ProgressBar, Integer)(AddressOf TH_SetPrgValue), prg, value) Else prg.Value += value End If End Sub The problem is the invokerequired never get to false it actually goes in to beginInvoke but never end in the Else section to set the value.

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  • Is there a straightforward way to have a thread-local instance variable?

    - by Dan Tao
    With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there any straightforward way to declare a class member as thread-local, meaning, each class instance gets an object per thread?

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  • In .NET Xml Serialization, is it possible to serialize a class with an enum property with different

    - by Lasse V. Karlsen
    I have a class, containing a list property, where the list contains objects that has an enum property. When I serialize this, it looks like this: <?xml version="1.0" encoding="ibm850"?> <test> <events> <test-event type="changing" /> <test-event type="changed" /> </events> </test> Is it possible, through attributes, or similar, to get the Xml to look like this? <?xml version="1.0" encoding="ibm850"?> <test> <events> <changing /> <changed /> </events> </test> Basically, use the property value of the enum as a way to determine the tag-name? Is using a class hierarchy (ie. creating subclasses instead of using the property value) the only way? Edit: After testing, it seems even a class-hierarchy won't actually work. If there is a way to structure the classes to get the output I want, even with sub-classes, that is also an acceptable answer. Here's a sample program that will output the above Xml (remember to hit Ctrl+F5 to run in Visual Studio, otherwise the program window will close immediately): using System; using System.Collections.Generic; using System.Xml.Serialization; namespace ConsoleApplication18 { public enum TestEventTypes { [XmlEnum("changing")] Changing, [XmlEnum("changed")] Changed } [XmlType("test-event")] public class TestEvent { [XmlAttribute("type")] public TestEventTypes Type { get; set; } } [XmlType("test")] public class Test { private List<TestEvent> _Events = new List<TestEvent>(); [XmlArray("events")] public List<TestEvent> Events { get { return _Events; } } } class Program { static void Main(string[] args) { Test test = new Test(); test.Events.Add(new TestEvent { Type = TestEventTypes.Changing }); test.Events.Add(new TestEvent { Type = TestEventTypes.Changed }); XmlSerializer serializer = new XmlSerializer(typeof(Test)); XmlSerializerNamespaces ns = new XmlSerializerNamespaces(); ns.Add("", ""); serializer.Serialize(Console.Out, test, ns); } } }

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  • Java array of arry [matrix] of an integer partition with fixed term

    - by user335209
    Hello, for my study purpose I need to build an array of array filled with the partitions of an integer with fixed term. That is given an integer, suppose 10 and given the fixed number of terms, suppose 5 I need to populate an array like this 10 0 0 0 0 9 0 0 0 1 8 0 0 0 2 7 0 0 0 3 ............ 9 0 0 1 0 8 0 0 1 1 ............. 7 0 1 1 0 6 0 1 1 1 ............ ........... 0 6 1 1 1 ............. 0 0 0 0 10 am pretty new to Java and am getting confused with all the for loops. Right now my code can do the partition of the integer but unfortunately it is not with fixed term public class Partition { private static int[] riga; private static void printPartition(int[] p, int n) { for (int i= 0; i < n; i++) System.out.print(p[i]+" "); System.out.println(); } private static void partition(int[] p, int n, int m, int i) { if (n == 0) printPartition(p, i); else for (int k= m; k > 0; k--) { p[i]= k; partition(p, n-k, n-k, i+1); } } public static void main(String[] args) { riga = new int[6]; for(int i = 0; i<riga.length; i++){ riga[i] = 0; } partition(riga, 6, 1, 0); } } the output I get it from is like this: 1 5 1 4 1 1 3 2 1 3 1 1 1 2 3 1 2 2 1 1 2 1 2 1 2 1 1 1 what i'm actually trying to understand how to proceed is to have it with a fixed terms which would be the columns of my array. So, am stuck with trying to get a way to make it less dynamic. Any help?

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  • Is there a straightforward way to have a ThreadStatic instance member?

    - by Dan Tao
    With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there some corresponding attribute that provides the same functionality, but for instance members? In other words, that allows me to have one instance of the object, per thread, per instance of the containing class?

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  • GWT: Reloading a single tab in a tab panel

    - by auste piliponyte
    I have a GWT tab panel and would like to reload a single tab when a certain event (e.g. button click) happens in another tab. Is there a way to do that? Another possibility would be executing some code (e.g. adding a new element to a tab) when that tab is selected. Any help would be really appreciated, I am stuck with this for a while already. To make the question more specific I am providing some code below. I have my code organized in screens, there is a home screen that initiates the tab panel. And there are separate screens for initiation of each tab. The simplified code for the home screen: public class HomeScreen extends Composite{ public HomeScreen() { TabPanel tabPanel = new TabPanel(); FlowPanel flowpanel; flowpanel = new FlowPanel(); ProfileTabScreen profileTabScreen = new ProfileTabScreen(); flowpanel.add(profileTabScreen); tabPanel.add(flowpanel, "Profile"); flowpanel = new FlowPanel(); GroupsTabScreen groupsTabScreen = new GroupsTabScreen(); flowpanel.add(groupsTabScreen); tabPanel.add(flowpanel, "Groups"); initWidget(tabPanel); } } Code for the tab screen from which I want to initiate the reload: private VerticalPanel groupPanel = new VerticalPanel(); private Button newGroupButton = new Button("New group"); public GroupsTabScreen() { newGroupButton.addClickHandler(new ClickHandler(){ public void onClick(ClickEvent event) { createNewGroup(); } }); groupPanel.add(newGroupButton); initWidget(groupPanel); } Code for the tab screen that has to be reloaded: private VerticalPanel profilePanel = new VerticalPanel(); private Label label = new Label("No groups yet."); public ProfileTabScreen() { profilePanel.add(label); initWidget(profilePanel); } So let's imagine I just want to change text of a label in profileTab (while in reality it will be ListBox and other elements), when the newGroupButton is clicked in groupTab. As I said, reloading the whole profileTab each time is is selected would be acceptable as well.

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  • passing Func<TSource, TKey> keySelector error

    - by user338429
    static void Main() { string[] a = { "a", "asd", "bdfsd", "we" }; a = a.OrderBy(fun).ToArray(); } private static int fun(string s) { return s.Length; } its is giving compile time error . I know that we can do this with Lambda expression like this. a.OrderBy(s=>s.Length).ToArray(); but i want to this do by defining different function . What mistake i have done?

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  • pointer to preallocated memory as an input parameter and have the function fill it

    - by djones2010
    test code: void modify_it(char * mystuff) { char test[7] = "123456"; //last element is null i presume for c style strings here. //static char test[] = "123123"; //when i do this i thought i should be able to gain access to this bit of memory when the function is destroyed but that does not seem to be the case. //char * test = new char[7]; //this is also creating memory on stack and not the heap i reckon and gets destroyed once the function is done with. strcpy_s(mystuff,7,test); //this does the job as long as memory for mystuff has been allocated outside the function. mystuff = test; //this does not work. I know with c style strings you can't just do string assignments they have to be actually copied. in this case I was using this in conjunction with static char test thinking by having it as static the memory would not get destroyed and i can then simply point mystuff to test and be done with it. i would later have address the memory cleanup in the main function. but anyway this never worked. } int main(void) { char * mystuff = new char [7]; //allocate memory on heap where the pointer will point cool(mystuff); std::string test_case(mystuff); std::cout<<test_case.c_str(); //this is the only way i know how to use cout by making it into a string c++ string. delete [] mystuff; return 0; } in the case, of a static array in the function why would it not work. in the case, when i allocated memory using new in the function does it get created on the stack or heap? in the case, i have string which needs to be copied into a char * form. everything i see usually requires const char* instead of just char*. I know i could use reference to take care of this easy. Or char ** to send in the pointer and do it that way. But i just wanted to know if I could do it with just char *. Anyway your thoughts and comments plus any examples would be very helpful.

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  • How to query a collection of inherited object for a particular object type in grails ?

    - by quilovnic
    Hi, I have a this model : class Question{ Set components static hasMany = [components: QuestionComponent] } class QuestionComponent{ static belongsTo = Question } class QuestionComponentStatus extends QuestionComponent{ } class QuestionComponentOther extends QuestionComponent{ } I want to get only QuestionComponentStatus from Set components : questionInstance.components. ? Thanks a lot

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  • C++ - Error: expected unqualified-id before ‘using’

    - by Francisco P.
    Hello, everyone. I am having some trouble on a project I'm working on. Here's the header file for the calor class: #ifndef _CALOR_ #define _CALOR_ #include "gradiente.h" using namespace std; class Calor : public Gradiente { public: Calor(); Calor(int a); ~Calor(); int getTemp(); int getMinTemp(); void setTemp(int a); void setMinTemp(int a); void mostraSensor(); }; #endif When I try to compile it: calor.h|6|error: expected unqualified-id before ‘using’| Why does this happen? I've been searching online and learned this error occurs mostly due to corrupted included files. Makes no sense to me, though. This class inherits from gradiente: #ifndef _GRADIENTE_ #define _GRADIENTE_ #include "sensor.h" using namespace std; class Gradiente : public Sensor { protected: int vActual, vMin; public: Gradiente(); ~Gradiente(); } #endif Which in turn inherits from sensor #ifndef _SENSOR_ #define _SENSOR_ #include <iostream> #include <fstream> #include <string> #include "definicoes.h" using namespace std; class Sensor { protected: int tipo; int IDsensor; bool estadoAlerta; bool estadoActivo; static int numSensores; public: Sensor(/*PARAMETROS*/); Sensor(ifstream &); ~Sensor(); int getIDsensor(); bool getEstadoAlerta(); bool getEstadoActivo(); void setEstadoAlerta(int a); void setEstadoActivo(int a); virtual void guardaSensor(ofstream &); virtual void mostraSensor(); // FUNÇÃO COMUM /* virtual int funcaoComum() = 0; virtual int funcaoComum(){return 0;};*/ }; #endif For completeness' sake, here's definicoes.h #ifndef _DEFINICOES_ #define _DEFINICOES_ const unsigned int SENSOR_MOVIMENTO = 0; const unsigned int SENSOR_SOM = 1; const unsigned int SENSOR_PRESSAO = 2; const unsigned int SENSOR_CALOR = 3; const unsigned int SENSOR_CONTACTO = 4; const unsigned int MIN_MOVIMENTO = 10; const unsigned int MIN_SOM = 10; const unsigned int MIN_PRESSAO = 10; const unsigned int MIN_CALOR = 35; #endif Any help'd be much appreciated. Thank you for your time. Thanks for your time!

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  • Flickering Image in Java?

    - by Noah Cagle
    OK so I am coding a game right now to prepair for Ludum Dare SharkJam, and I am using a new method for programming, because the last method I had crashes my PC, so this one should work. Well it does work and all, better too, but the images that I put in it flicker. Here is the whole main class (where the images are drawn) package me.NoahCagle.watermaze; import java.awt.Color; import java.awt.Graphics; import java.awt.Image; import java.awt.image.BufferedImage; import javax.swing.JFrame; import me.NoahCagle.watermaze.entity.EntityShark; import me.NoahCagle.watermaze.entity.Player; import me.NoahCagle.watermaze.input.Keys; import me.NoahCagle.watermaze.map.Map; public class Game extends JFrame { private static final long serialVersionUID = 1L; Map map = new Map(0, 0); Player player = new Player(50, 30); static EntityShark shark = new EntityShark(400, 400); public Image dbImage; public Game() { setSize(800, 600); setDefaultCloseOperation(EXIT_ON_CLOSE); setLocationRelativeTo(null); setVisible(true); setTitle("Water Maze"); setResizable(false); setBackground(Color.blue); addKeyListener(new Keys()); } public static void main(String[] args) { new Game(); Thread s = new Thread(shark); s.start(); } public void paint(Graphics g) { dbImage = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB); g.drawImage(dbImage, map.x, map.y, null); g.drawImage(player.player, player.x, player.y, this); g.drawImage(shark.shark, shark.x, shark.y, this); repaint(); } } What this code does for me is makes the Images work correctly, just flickering, alot. Can anyone help me with my issue? EDIT: I think it has something to do with where I call the repaint method in the paint method, so look there.

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  • Function defined but not used in C

    - by thetna
    I have following code: static __inline__ LIST list_List(POINTER P) { return list_Cons(P,list_Nil()); } After compilation I got following warning: inlining is unlikely but function size may grow I removed the inline and changed into the following : static LIST list_List(POINTER P) { return list_Cons(P,list_Nil()); } Now I get the following warning: list_List is defined but not used. Can anybody please suggest me how can remove that warning.

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  • Java overloading and overriding

    - by Padmanabh
    We always say that method overloading is static polymorphism and overriding is runtime polymorphism. What exactly do we mean by static here? Is the call to a method resolved on compiling the code? So whats the difference between normal method call and calling a final method? Which one is linked at compile time?

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  • Resolve instance - Autofac

    - by user137348
    I'm trying to figure out how to resolve a instance somewhere in the code. At the application startup I registered a type static void Main() { var builder = new ContainerBuilder(); builder.RegisterType<Foo>().As<IFoo>(); } Now, how can I resolve an instance somewhere in the code ? In structure mam there is a static object ObjectFactory.GetInstance<IFoo>()

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  • Thread won't stop when I want it to? (Java)

    - by Stuart
    I have a thread in my screen recording application that won't cooperate: package recorder; import java.awt.AWTException; import java.awt.Insets; import java.io.IOException; import javax.swing.JFrame; public class RepeatThread extends Thread { boolean stop; public volatile Thread recordingThread; JFrame frame; int count = 0; RepeatThread( JFrame myFrame ) { stop = false; frame = myFrame; } public void run() { while( stop == false ) { int loopDelay = 33; // 33 is approx. 1000/30, or 30 fps long loopStartTime = System.currentTimeMillis(); Insets insets = frame.getInsets(); // Get the shape we're recording try { ScreenRecorder.capture( frame.getX() + insets.left, frame.getY() + insets.top, frame.getWidth() - ( insets.left + insets.right ), frame.getHeight() - ( insets.top + insets.bottom ) ); } catch( AWTException e1 ) { // TODO Auto-generated catch block e1.printStackTrace(); } catch( IOException e1 ) { // TODO Auto-generated catch block e1.printStackTrace(); } // Add another picture long loopEndTime = System.currentTimeMillis(); int loopTime = (int )( loopEndTime - loopStartTime ); if( loopTime < loopDelay ) { try { sleep( loopDelay - loopTime ); // If we have extra time, // sleep } catch( Exception e ) { } // If something interrupts it, I don't give a crap; just // ignore it } } } public void endThread() { stop = true; count = 0; ScreenRecorder.reset(); // Once I get this annoying thread to work, I have to make the pictures // into a video here! } } It's been bugging me for ages. It periodically takes screenshots to the specified area. When you start recording, it hides (decativates) the window. On a Mac, when you give an application focus, any hidden windows will activate. In my class WListener (which I have confirmed to work), I have: public void windowActivated(WindowEvent e) { if(ScreenRecorder.recordingThread != null) { ScreenRecorder.recordingThread.endThread(); } } So what SHOULD happen is, the screenshot-taking thread stops when he clicks on the application. However, I must be brutally screwing something up, because when the thread is running, it won't even let the window reappear. This is my first thread, so I expected a weird problem like this. Do you know what's wrong?

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  • Why my java app for android not connect to server?

    - by FredVaz
    Why my java app for android not connect to server ? I run the aplication in android emulator, and the server wich port 9999 and host 127.0.0.1 in my pc, but just not connect and i think this method isn't good for android app. It is my source code: import android.app.Activity; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; //Java imports //import android.util.Log; import java.io.*; import java.net.*; import java.util.*; import java.util.logging.Level; import java.util.logging.Logger; public class MainActivity extends Activity { //Variaveis Interface private Button ligar; private Button enviar; private EditText text1; private TextView text2; //Variaveis static Socket cSocket; static PrintWriter out; static BufferedReader in; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //Declaração butões ligar = (Button) findViewById(R.id.ligar); enviar = (Button) findViewById(R.id.enviar); text1 = (EditText) findViewById(R.id.text1); text2 = (TextView) findViewById(R.id.text2); //Interacao ligar.setOnClickListener(new OnClickListener(){ public void onClick(View arg0){ connect(); } }); enviar.setOnClickListener(new OnClickListener(){ public void onClick(View arg0){ out.println("Hello"); text2.setText(""); } }); } //Outras Funcoes public void connect(){ //Funcao ligar cSocket = null; out = null; in = null; try { cSocket = new Socket("127.0.0.1",9999); out = new PrintWriter(cSocket.getOutputStream(), true); in = new BufferedReader(new InputStreamReader(cSocket.getInputStream())); text2.setText("Estas conectado com sucesso."); } catch (IOException ex) { //Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex); text2.setText("Erro! Na conexão"); } } // }

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  • Is it thread safe to read a form controls value (but not change it) without using Invoke/BeginInvoke from another thread

    - by goku_da_master
    I know you can read a gui control from a worker thread without using Invoke/BeginInvoke because my app is doing it now. The cross thread exception error is not being thrown and my System.Timers.Timer thread is able to read gui control values just fine (unlike this guy: can a worker thread read a control in the GUI?) Question 1: Given the cardinal rule of threads, should I be using Invoke/BeginInvoke to read form control values? And does this make it more thread-safe? The background to this question stems from a problem my app is having. It seems to randomly corrupt form controls another thread is referencing. (see question 2) Question 2: I have a second thread that needs to update form control values so I Invoke/BeginInvoke to update those values. Well this same thread needs a reference to those controls so it can update them. It holds a list of these controls (say DataGridViewRow objects). Sometimes (not always), the DataGridViewRow reference gets "corrupt". What I mean by corrupt, is the reference is still valid, but some of the DataGridViewRow properties are null (ex: row.Cells). Is this caused by question 1 or can you give me any tips on why this might be happening? Here's some code (the last line has the problem): public partial class MyForm : Form { void Timer_Elapsed(object sender) { // we're on a new thread (this function gets called every few seconds) UpdateUiHelper updateUiHelper = new UpdateUiHelper(this); foreach (DataGridViewRow row in dataGridView1.Rows) { object[] values = GetValuesFromDb(); updateUiHelper.UpdateRowValues(row, values[0]); } // .. do other work here updateUiHelper.UpdateUi(); } } public class UpdateUiHelper { private readonly Form _form; private Dictionary<DataGridViewRow, object> _rows; private delegate void RowDelegate(DataGridViewRow row); private readonly object _lockObject = new object(); public UpdateUiHelper(Form form) { _form = form; _rows = new Dictionary<DataGridViewRow, object>(); } public void UpdateRowValues(DataGridViewRow row, object value) { if (_rows.ContainsKey(row)) _rows[row] = value; else { lock (_lockObject) { _rows.Add(row, value); } } } public void UpdateUi() { foreach (DataGridViewRow row in _rows.Keys) { SetRowValueThreadSafe(row); } } private void SetRowValueThreadSafe(DataGridViewRow row) { if (_form.InvokeRequired) { _form.Invoke(new RowDelegate(SetRowValueThreadSafe), new object[] { row }); return; } // now we're on the UI thread object newValue = _rows[row]; row.Cells[0].Value = newValue; // randomly errors here with NullReferenceException, but row is never null! }

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