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• Swing object: first setText() gets "stuck" when using Mac Java SE 6

  - by Tim

  Hi there, I am a Java newbie trying to maintain an application that works fine under J2SE 5.0 (32- and 64-bit) but has a very specific problem when run under Java SE 6 64-bit: [Tims-MPB:~] tlynch% java -version java version "1.6.0_15" Java(TM) SE Runtime Environment (build 1.6.0_15-b03-226) Java HotSpot(TM) 64-Bit Server VM (build 14.1-b02-92, mixed mode) The application is cross-platform and reportedly works correctly on Java SE 6 under Windows, though I haven't been able to verify that myself. The program uses a JTextField for some text entry and a JLabel to indicate the text to be entered. The first time the showDialog() method is called to set the label text and display the dialog, it works correctly, but subsequent calls all result in the display of the label from the initial invocation rather than the one most recently specified via setText(). public void showDialog(String msgText) { System.out.println("set ChatDialog: " + msgText); jLabel1.setText(msgText); jLabel1.repaint(); // I added this; it didn't help System.out.println("get ChatDialog: " + jLabel1.getText()); super.setVisible(true); } [the full text of the class is provided below] The added printlns validate that expected text is passed to the label's setText() method and is confirmed by retrieving it using getText(), but what shows up on the screen/GUI is always the text from the very first time the method was called for the object. A similar issue is observed with a JTextArea used to label another dialog box. These problem are consistent across multiple Mac systems running Java SE 6 under OS 10.5.x and 10.6.x, but they are never observed when one reverts to J2SE 5.0. If there is some background information pertinent to this problem that I have omitted, please let me know. Any insights or advice appreciated. package gui; import java.awt.*; import java.awt.event.KeyEvent; import javax.swing.*; // Referenced classes of package gui: // MyJPanel, ChatDialog_jTextField1_keyAdapter, WarWindow public class ChatDialog extends JDialog { public ChatDialog(JFrame parent, WarWindow w) { super(parent, true); text = ""; borderLayout1 = new BorderLayout(); jPanel1 = new MyJPanel(); borderLayout2 = new BorderLayout(); jPanel2 = new MyJPanel(); jPanel3 = new MyJPanel(); jLabel1 = new JLabel(); jTextField1 = new JTextField(); warWindow = w; try { jbInit(); } catch(Exception exception) { System.out.println("Problem with ChatDialog init"); exception.printStackTrace(); } return; } public String getText() { return text; } void jTextField1_keyPressed(KeyEvent e) { int id = e.getKeyCode(); switch(id) { case 10: // '\n' text = jTextField1.getText(); setVisible(false); break; } } private void jbInit() throws Exception { setLocation(232, 450); setSize(560, 60); setModal(true); setResizable(false); setUndecorated(true); getContentPane().setLayout(borderLayout1); jPanel1.setLayout(borderLayout2); jPanel2.setMinimumSize(new Dimension(10, 20)); jPanel2.setPreferredSize(new Dimension(10, 20)); jLabel1.setPreferredSize(new Dimension(380, 15)); jLabel1.setHorizontalAlignment(0); jLabel1.setText("Chat Message"); jTextField1.setPreferredSize(new Dimension(520, 21)); jTextField1.setRequestFocusEnabled(false); jTextField1.addKeyListener(new ChatDialog_jTextField1_keyAdapter(this)); getContentPane().add(jPanel1, "Center"); jPanel1.add(jPanel2, "North"); jPanel2.add(jLabel1, null); jPanel1.add(jPanel3, "Center"); jPanel3.add(jTextField1, null); } public void setVisible(boolean b) { jTextField1.setText(""); super.setVisible(b); } public void showDialog(String msgText) { System.out.println("set ChatDialog: " + msgText); jLabel1.setText(msgText); jLabel1.repaint(); // I added this; it didn't help System.out.println("get ChatDialog: " + jLabel1.getText()); super.setVisible(true); } void this_keyPressed(KeyEvent e) { int id = e.getKeyCode(); switch(id) { case 10: // '\n' System.exit(88); break; } } BorderLayout borderLayout1; BorderLayout borderLayout2; JLabel jLabel1; JPanel jPanel1; JPanel jPanel2; JPanel jPanel3; JTextField jTextField1; String text; WarWindow warWindow; }

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• Kickoff and Krunner to search with less than 3 chars in search field?

  - by Benjamin

  Both Krunner and Kickoff in Kubuntu return a list of found items after the user has entered at least three characters in the search field. Usage on Synapse shows that returning a list after one character onwards is faster and efficient. I would like Kickoff and Krunner to behave similarly, by making the return a list of items after entering the first character in their search field. How can I achieve that?

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• Inheriting the main method

  - by Eric

  I want to define a base class that defines a main method that instantiates the class, and runs a method. There are a couple of problems though. Here is the base class: public abstract class Strategy { abstract void execute(SoccerRobot robot); public static void main(String args) { Strategy s = new /*Not sure what to put here*/(); s.execute(new SoccerRobot()) } } And here is an example derived class: public class UselessStrategy { void execute(SoccerRobot robot) { System.out.println("I'm useless") } } It defines a simple execute method, which should be called in a main method upon usage as a the main application. However, in order to do so, I need to instantiate the derived class from within the base class's main method. Which doesn't seem to be possible. I'd rather not have to repeat the main method for every derived class, as it feels somewhat unnessary. Is there a right way of doing this?

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• Checking timeouts made more readable

  - by Markus

  I have several situations where I need to control timeouts in a technical application. Either in a loop or as a simple check. Of course – handling this is really easy, but none of these is looking cute. To clarify, here is some C# (Pseudo) code: private DateTime girlWentIntoBathroom; girlWentIntoBathroom = DateTime.Now; do { // do something } while (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now); or if (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); Now I was inspired by something a saw in Ruby on StackOverflow: Now I’m wondering if this construct can be made more readable using extension methods. My goal is something that can be read like “If girlWentIntoBathroom is more than 10 seconds ago” 1st attempt if (girlWentIntoBathroom > (10).Seconds().Ago()) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); So I wrote an extension for integer that converts the integer into a TimeSpan public static TimeSpan Seconds(this int amount) { return new TimeSpan(0, 0, amount); } After that, I wrote an extension for TimeSpan like this: public static DateTime Ago(this TimeSpan diff) { return DateTime.Now.Add(-diff); } This works fine so far, but has a great disadvantage. The logic is inverted! Since girlWentIntoBathroom is a timestamp in the past, the right side of the equation needs to count backwards: impossible. Just inverting the equation is no solution, because it will invert the read sentence as well. 2nd attempt So I tried something new: if (girlWentIntoBathroom.IsMoreThan(10).SecondsAgo()) MessageBox.Show("Knock louder"); else MessageBox.Show("Wait a little longer"); IsMoreThan() needs to transport the past timestamp as well as the span for the extension SecondsAgo(). It could be: public static DateWithIntegerSpan IsMoreThan(this DateTime baseTime, int span) { return new DateWithIntegerSpan() { Date = baseTime, Span = span }; } Where DateWithIntegerSpan is simply: public class DateWithIntegerSpan { public DateTime Date {get; set;} public int Span { get; set; } } And SecondsAgo() is public static bool SecondsAgo(this DateWithIntegerSpan dateAndSpan) { return dateAndSpan.Date.Add(new TimeSpan(0, 0, dateAndSpan.Span)) < DateTime.Now; } Using this approach, the English sentence matches the expected behavior. But the disadvantage is, that I need a helping class (DateWithIntegerSpan). Has anyone an idea to make checking timeouts look more cute and closer to a readable sentence? Am I a little too insane thinking about something minor like this?

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• &lt;%: %&gt;, HtmlEncode, IHtmlString and MvcHtmlString

  - by Shaun

  One of my colleague and friend, Robin is playing and struggling with the ASP.NET MVC 2 on a project these days while I’m struggling with a annoying client. Since it’s his first time to use ASP.NET MVC he was meetings with a lot of problem and I was very happy to share my experience to him. Yesterday he asked me when he attempted to insert a <br /> element into his page he found that the page was rendered like this which is bad. He found his <br /> was shown as a part of the string rather than creating a new line. After checked a bit in his code I found that it’s because he utilized a new ASP.NET markup supported in .NET 4.0 – “<%: %>”. If you have been using ASP.NET MVC 1 or in .NET 3.5 world it would be very common that using <%= %> to show something on the page from the backend code. But when you do it you must ensure that the string that are going to be displayed should be Html-safe, which means all the Html markups must be encoded. Otherwise this might cause an XSS (cross-site scripting) problem. So that you’d better use the code like this below to display anything on the page. In .NET 4.0 Microsoft introduced a new markup to solve this problem which is <%: %>. It will encode the content automatically so that you will no need to check and verify your code manually for the XSS issue mentioned below. But this also means that it will encode all things, include the Html element you want to be rendered. So I changed his code like this and it worked well. After helped him solved this problem and finished a spreadsheet for my boring project I considered a bit more on the <%: %>. Since it will encode all thing why it renders correctly when we use “<%: Html.TextBox(“name”) %>” to show a text box? As you know the Html.TextBox will render a “<input name="name" id="name" type="text"/>” element on the page. If <%: %> will encode everything it should not display a text box. So I dig into the source code of the MVC and found some comments in the class MvcHtmlString. 1: // In ASP.NET 4, a new syntax <%: %> is being introduced in WebForms pages, where <%: expression %> is equivalent to 2: // <%= HttpUtility.HtmlEncode(expression) %>. The intent of this is to reduce common causes of XSS vulnerabilities 3: // in WebForms pages (WebForms views in the case of MVC). This involves the addition of an interface 4: // System.Web.IHtmlString and a static method overload System.Web.HttpUtility::HtmlEncode(object). The interface 5: // definition is roughly: 6: // public interface IHtmlString { 7: // string ToHtmlString(); 8: // } 9: // And the HtmlEncode(object) logic is roughly: 10: // - If the input argument is an IHtmlString, return argument.ToHtmlString(), 11: // - Otherwise, return HtmlEncode(Convert.ToString(argument)). 12: // 13: // Unfortunately this has the effect that calling <%: Html.SomeHelper() %> in an MVC application running on .NET 4 14: // will end up encoding output that is already HTML-safe. As a result, we're changing out HTML helpers to return 15: // MvcHtmlString where appropriate. <%= Html.SomeHelper() %> will continue to work in both .NET 3.5 and .NET 4, but 16: // changing the return types to MvcHtmlString has the added benefit that <%: Html.SomeHelper() %> will also work 17: // properly in .NET 4 rather than resulting in a double-encoded output. MVC developers in .NET 4 will then be able 18: // to use the <%: %> syntax almost everywhere instead of having to remember where to use <%= %> and where to use 19: // <%: %>. This should help developers craft more secure web applications by default. 20: // 21: // To create an MvcHtmlString, use the static Create() method instead of calling the protected constructor. The comment said the encoding rule of the <%: %> would be: If the type of the content is IHtmlString it will NOT encode since the IHtmlString indicates that it’s Html-safe. Otherwise it will use HtmlEncode to encode the content. If we check the return type of the Html.TextBox method we will find that it’s MvcHtmlString, which was implemented the IHtmlString interface dynamically. That is the reason why the “<input name="name" id="name" type="text"/>” was not encoded by <%: %>. So if we want to tell ASP.NET MVC, or I should say the ASP.NET runtime that the content is Html-safe and no need, or should not be encoded we can convert the content into IHtmlString. So another resolution would be like this. Also we can create an extension method as well for better developing experience. 1: using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Web; 5: using System.Web.Mvc; 6:  7: namespace ShaunXu.Blogs.IHtmlStringIssue 8: { 9: public static class Helpers 10: { 11: public static MvcHtmlString IsHtmlSafe(this string content) 12: { 13: return MvcHtmlString.Create(content); 14: } 15: } 16: } Then the view would be like this. And the page rendered correctly.         Summary In this post I explained a bit about the new markup in .NET 4.0 – <%: %> and its usage. I also explained a bit about how to control the page content, whether it should be encoded or not. We can see the ASP.NET MVC gives us more points to control the web pages.   Hope this helps, Shaun All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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• how to modify a textbox using remoting

  - by danutz0119

  I am trying to modify a textBox found in the server Form using remoting from the client side. i have tried some solutions i found, but none of them work. the remoting part works propperly, the only thing that I am not able to figure out is this: this is what i have: client side: ... private void btn_b1_Click(object sender, EventArgs e) { ... myFunc.update(string s); ... } ... sharedLibs: public interface myInterf { void update(string s); } server side: here i have 2 classes in the same namespace class class1 : MarshalByRefObject, myInterf { public void update(string s) { //what do i write here to modify textBox1? } } public partial class class2 : Form { ... // here is the textBox i am trying to alter; }

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• "Thread-Safe Calls" with "Invoke" method to Winform control leads very heavy memory leak!!

  - by konnychen

  In the following link: "Make Thread-Safe Calls to Windows Forms Controls http://msdn.microsoft.com/en-us/library/ms171728.aspx" We can see an example which provide cross tread access to a winform control. But if the thread is in a while loop, it will cause the heavy memory leak. As I use taskmanage I can see the memory is increasing. Can anyone help me to solve the problem? oThread2 = new Thread(new ThreadStart(Cyclic_Call)); oThread2.Start(); delegate void SetText_lab_Statubar(string text); private void m_SetText_lab_Statubar(string text) { if (this.lab_Statubar.InvokeRequired) { SetText_lab_Statubar d = new SetText_lab_Statubar(m_SetText_lab_Statubar); this.Invoke(d, new object[] { text }); } else { this.lab_Statubar.Text = text; } } private void Cyclic_Call() { do { this.m_SetText_lab_Statubar("This string is set from thread"); Thread.Sleep(100); } while (!b_AbortThraed); }

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• NSAutoreleasePool carrying across methods?

  - by Tim

  I'm building an iPhone application where I detach some threads to do long-running work in the background so as not to hang the UI. I understand that threads need NSAutoreleasePool instances for memory management. What I'm not sure about is if the threaded method calls another method - does that method also need an NSAutoreleasePool? Example code: - (void)primaryMethod { [self performSelectorInBackground:@selector(threadedMethod) withObject:nil]; } - (void)threadedMethod { NSAutoreleasePool *aPool = [[NSAutoreleasePool alloc] init]; // Some code here [self anotherMethod]; // Maybe more code here [aPool drain]; } - (void)anotherMethod { // More code here } The reason I ask is I'm receiving errors that objects are being autoreleased with no pool in place, and are "just leaking." I've seen other questions where people didn't have autorelease pools in place at all, and I understand why an autorelease pool is needed. I'm specifically interested in finding out whether an autorelease pool created in (in this example) threadedMethod applies to objects created in anotherMethod.

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• How to call a method of a specific class from another class (created in this specific class) ?

  - by choise

  I created a TTModelViewController. in the createModel Method i created a TTURLRequestModel. after Loading content in the TTURLRequestModel i want to call a method in my TTModelViewController. TTModelViewController - (void) createModel { requestModel = [[singlePostModel alloc] initWithId:@"54"]; } - (void)didLoadModel:(BOOL)firstTime { NSLog(@"loaded"); } TTURLRequestModel (singlePostModel) - (void)requestDidFinishLoad:(TTURLRequest*)request { //doing something [super requestDidFinishLoad:request]; } first i thought "didLoadModel" gets called after requestDidFinishLoad was called, but its before. So, how can i call a method in my TTModelViewController after request is finished loading? is there a method that already does that and i only have to overwrite this? or something else? thanks // if knowbody knows how to do this with three20, anybody can tell me how to do this in general?

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• When do I need to deallocate memory?

  - by extintor

  I am using this code inside a class to make a webbrowser control visit a website: void myClass::visitWeb(const char *url) { WCHAR buffer[MAX_LEN]; ZeroMemory(buffer, sizeof(buffer)); MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, url, strlen(url), buffer, sizeof(buffer)-1); VARIANT vURL; vURL.vt = VT_BSTR; vURL.bstrVal = SysAllocString(buffer); // webbrowser navigate code... VariantClear(&vURL); } I call visitWeb from another void function that gets called on the handlemessage() for the app. Do I need to do some memory deallocation here?, I see vURL is being deallocated by VariantClear but should I deallocate memory for buffer? I've been told that in another bool I have in the same app I shouldn't deallocate anything because everything clear out when the bool return true/false, but what happens on this void?

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• Threads to make video out of images

  - by masood

  updates: I think/ suspect the imageIO is not thread safe. shared by all threads. the read() call might use resources that are also shared. Thus it will give the performance of a single thread no matter how many threads used. ? if its correct . what is the solution (in practical code) Single request and response model at one time do not utilizes full network/internet bandwidth, thus resulting in low performance. (benchmark is of half speed utilization or even lower) This is to make a video out of an IP cam that gives a new image on each request. http://149.5.43.10:8001/snapshot.jpg It makes a delay of 3 - 8 seconds no matter what I do. Changed thread no. and thread time intervals, debugged the code by System.out.println statements to see if threads work. All seems normal. Any help? Please show some practical code. You may modify mine. This code works (javascript) with much smoother frame rate and max bandwidth usage. but the later code (java) dont. same 3 to 8 seconds gap. <!DOCTYPE html> <html> <head> <script type="text/javascript"> (function(){ var img="/*url*/"; var interval=50; var pointer=0; function showImg(image,idx) { if(idx<=pointer) return; document.body.replaceChild(image,document.getElementsByTagName("img")[0]); pointer=idx; preload(); } function preload() { var cache=null,idx=0;; for(var i=0;i<5;i++) { idx=Date.now()+interval*(i+1); cache=new Image(); cache.onload=(function(ele,idx){return function(){showImg(ele,idx);};})(cache,idx); cache.src=img+"?"+idx; } } window.onload=function(){ document.getElementsByTagName("img")[0].onload=preload; document.getElementsByTagName("img")[0].src="/*initial url*/"; }; })(); </script> </head> <body> <img /> </body> </html> and of java (with problem) : package camba; import java.applet.Applet; import java.awt.Button; import java.awt.Graphics; import java.awt.Image; import java.awt.Label; import java.awt.Panel; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.net.URL; import java.security.Timestamp; import java.util.Date; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicBoolean; import javax.imageio.ImageIO; public class Camba extends Applet implements ActionListener{ Image img; TextField textField; Label label; Button start,stop; boolean terminate = false; long viewTime; public void init(){ label = new Label("please enter camera URL "); add(label); textField = new TextField(30); add(textField); start = new Button("Start"); add(start); start.addActionListener(this); stop = new Button("Stop"); add(stop); stop.addActionListener(this); } public void actionPerformed(ActionEvent e){ Button source = (Button)e.getSource(); if(source.getLabel() == "Start"){ for (int i = 0; i < 7; i++) { myThread(50*i); } System.out.println("start..."); } if(source.getLabel() == "Stop"){ terminate = true; System.out.println("stop..."); } } public void paint(Graphics g) { update(g); } public void update(Graphics g){ try{ viewTime = System.currentTimeMillis(); g.drawImage(img, 100, 100, this); } catch(Exception e) { e.printStackTrace(); } } public void myThread(final int sleepTime){ new Thread(new Runnable() { public void run() { while(!terminate){ try { TimeUnit.MILLISECONDS.sleep(sleepTime); } catch (InterruptedException ex) { ex.printStackTrace(); } long requestTime= 0; Image tempImage = null; try { URL pic = null; requestTime= System.currentTimeMillis(); pic = new URL(getDocumentBase(), textField.getText()); tempImage = ImageIO.read(pic); } catch(Exception e) { e.printStackTrace(); } if(requestTime >= /*last view time*/viewTime){ img = tempImage; Camba.this.repaint(); } } }}).start(); System.out.println("thread started..."); } }

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• Can running object be garbage collected?

  - by Kugel

  I have a simple class: public class Runner { public void RunAndForget(RunDelegate method) { ThreadPool.QueueUserWorkItem(new WaitCallback(Run), method); } private void Run(object o) { ((RunDelegate )o).Invoke(); } } And if I use this like so: private void RunSomethingASync() { Runner runner = new Runner(); runner.FireAndForget(new RunDelegate(Something)); } Is there any danger using it like this? My C++ guts tell me that runner object should be destroyed after RunSomethingASync is finished. Am I right? What happens then to the method running on different thread? Or perhaps it is other way around and runner will not be collected? That would be a problem considering I may call RunSomethingASync() many times.

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• C++ -- typedef "inside" template arguments?

  - by redmoskito

  Imagine I have a template function like this: template<Iterator> void myfunc(Iterator a, Iterator::value_type b) { ... } Is there a way to declare a typedef for Iterator::valuetype that I can use in the function signature? For example: template< typename Iterator, typedef Iterator::value_type type> void myfunc(Iterator a, type b) { ... } Thus far, I've resorted to using default template arguments and Boost concept checking to ensure the default is always used: template< typename Iterator, typename type = Iterator::value_type > void myfunc(Iterator a, type b) { BOOST_STATIC_ASSERT(( boost::type_traits::is_same< typename Iterator::value_type, type >::value )); ... } ...but it would be nice if there was support in the language for this type of thing.

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• How does C++ free the memory when a constructor throws an exception and a custom new is used

  - by Joshua

  I see the following constructs: new X will free the memory if X constructor throws. operator new() can be overloaded. The canonical definition of an operator new overload is void *operator new(heap h) and the corrisponding operator delete. The most common operator new overload is pacement new, which is void *operator new(void *p) { return p; } You almost always cannot call delete on the pointer given to placement new. This leads to a single question. How is memory cleaned up when X constructor throws and an overloaded new is used?

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• Why baseclass calls method of subclass?

  - by twlkyao

  I encounter some code like the following: BaseClass: public class BaseClass { String name = "Base"; public BaseClass() { printName(); } public void printName() { System.out.println(name + "——Base"); } } DrivedClass: public class SubClass extends BaseClass { String name = "Sub"; public SubClass() { printName(); } public void printName() { System.out.println(name + "——Sub"); } public static void main(String[] args) { new SubClass(); } } When run the code, the output is: null——Sub Sub——Sub while it should be: Base——Base Sub——Sub I wonder why the BaseClass constructor calls the SubClass method, can anybody explain this? Thanks in advance.

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• UIViewScrollviw UITableView subview scrolling. IOS

  - by user1484810

  I have a UIScrollview with a UITableview subview. The UIScrollview scrolls the UITableView horizontally. The UITable view naturally scrolls up and down. If a user places their finger on the UitableView, and moves (swipes) horizontally, The delegate method below is invoked (void)scrollViewDidScroll:(UIScrollView *)scrollView with scrollView isEqual theUIScrollView If the user lifts their finger and places it back down on the UITableView and moves in a vertical direction The delegate method below is invoked (void)scrollViewDidScroll:(UIScrollView *)scrollView with scrollView isEqual = theUITable If however the user places their finger and moves in a horizontally (void)scrollViewDidScroll:(UIScrollView *)scrollView with scrollView isEqual theUIScrollView If the user then moves the finger (without lifting it) in a vertical direction. delegate method scrollViewDidScroll is not invoked at all. (The reverse is true too.) I note that the "Pulse News" app seems to behave in the above manner.. Ultimately I want to figure out how to get the UITableView and UIScrollview moving in a "unidirectional" fashion, with one finger kept on the screen. Thanks...

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• How to make an ambiguous call distinct in C++?

  - by jcyang

  void outputString(const string &ss) { cout << "outputString(const string& ) " + ss << endl; } void outputString(const string ss) { cout << "outputString(const string ) " + ss << endl; } int main(void) { //! outputString("ambigiousmethod"); const string constStr = "ambigiousmethod2"; //! outputString(constStr); } ///:~ How to make distinct call? EDIT: This piece of code could be compiled with g++ and msvc. thanks.

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• Retour de fonctions ou exceptions ? Une traduction de LittleWhite

  Bonjour à tous, Lorsqu'une erreur se produit dans une fonction, un développeur C++ a deux solutions : il peut soit retourner une valeur indiquant une erreur (par exemple avec return false; ou return ERROR_CODE;), soit lancer une exception. Mais quelle est la meilleure approche ? Dans cet article, Aaron Lahman apporte des éléments de réponse à cette question cruciale en regardant les différences en terme de lisibilité et d...

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• Why do I have to specify virtual functions in the declaration of a derived class?

  - by neuviemeporte

  Given the base class A and the derived class B: class A { public: virtual void f(); } class B : public A { public: void g(); } I get errors saying that f() is not declared in B while trying do define void B::f(). Do I have to declare f() explicitly in B? I think that if the interface changes I shouldn't have to correct the declarations in every single class deriving from it. Is there no way for B to get all the virtual functions' declarations from A automatically?

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• How can I push a string from one client connected to a WCF service to another connected as well?

  - by Sergio Tapia

  Here's what I have so far: IService: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.ServiceModel; namespace ServiceLibrary { [ServiceContract(SessionMode = SessionMode.Allowed, CallbackContract = typeof(IServiceCallback))] public interface IService { [OperationContract(IsOneWay = false, IsInitiating = true, IsTerminating = false)] void Join(string userName); } interface IServiceCallback { [OperationContract(IsOneWay = true)] void UserJoined(string senderName); } } Service: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.ServiceModel; namespace ServiceLibrary { [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession, ConcurrencyMode = ConcurrencyMode.Multiple)] public class Service:IService { IServiceCallback callback = null; public void Join(string userName) { callback = OperationContext.Current.GetCallbackChannel<IServiceCallback>(); } } } Just a simple string passed from one client to another.

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• Using a general class for execution with try/catch/finally?

  - by antirysm

  I find myself having a lot of this in different methods in my code: try { runABunchOfMethods(); } catch (Exception ex) { logger.Log(ex); } What about creating this: public static class Executor { private static ILogger logger; public delegate void ExecuteThis(); static Executor() { // logger = ...GetLoggerFromIoC(); } public static void Execute(ExecuteThis executeThis) { try { executeThis(); } catch (Exception ex) { logger.Log(ex); } } } And just using it like this: private void RunSomething() { Method1(someClassVar); Method2(someOtherClassVar); } ... Executor.Execute(RunSomething); Are there any downsides to this approach? (You could add Executor-methods and delegates when you want a finally and use generics for the type of Exeception you want to catch...)

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• Enforcing an "end" call whenever there is a corresponding "start" call

  - by Jeff Meatball Yang

  Let's say I want to enforce a rule: Everytime you call "StartJumping()" in your function, you must call "EndJumping()" before you return. When a developer is writing their code, they may simply forget to call EndSomething - so I want to make it easy to remember. I can think of only one way to do this: and it abuses the "using" keyword: class Jumper : IDisposable { public Jumper() { Jumper.StartJumping(); } public void Dispose() { Jumper.EndJumping(); } public static void StartJumping() {...} public static void EndJumping() {...} } public bool SomeFunction() { // do some stuff // start jumping... using(Jumper j = new Jumper()) { // do more stuff // while jumping } // end jumping } Is there a better way to do this?

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• Why aren't operator conversions implicitly called for templated functions? (C++)

  - by John Gordon

  I have the following code: template <class T> struct pointer { operator pointer<const T>() const; }; void f(pointer<const float>); template <typename U> void tf(pointer<const float>); void g() { pointer<float> ptr; f(ptr); tf(ptr); } When I compile the code with gcc 4.3.3 I get a message (aaa.cc:17: error: no matching function for call to ‘tf(pointer<float>&)’) indicating that the compiler called 'operator pointer<const T>' for the non-templated function f(), but didn't for the templated function tf(). Why and is there any workaround short of overloading tf() with a const and non-const version? Thanks in advance for any help.

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• Comparison between pointer and integer (cocoa)

  - by Cal S

  Hi, I'm just learning cocoa (coming from C#) but I'm getting a strange error for something that seems really simple... (charsSinceLastUpdate=36) #import "CSMainController.h" @implementation CSMainController //global vars int *charsSinceLastUpdate = 0; NSString *myString = @"Hello world"; // - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { ... } //other functions - (void)textDidChange:(NSNotification *)aNotification { NSLog(@"charsSinceLastUpdate=%i",charsSinceLastUpdate); if (charsSinceLastUpdate>=36) { // <- THIS line returns the error: Comparison between pointer and integer charsSinceLastUpdate=0; [statusText setStringValue:@"Will save now!"]; } else { charsSinceLastUpdate++; [statusText setStringValue:@"Not saving"]; } } //my functions - (void)showNetworkErrorAlert:(BOOL)showContinueWithoutSavingOption { ... } // @end Any help would be appreciated, thanks!

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• error: typedef name may not be a nested-name-specifier

  - by Autopulated

  I am trying to do something along the lines of this answer, and struggling: $ gcc --version gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) file.cpp:7: error: template argument 1 is invalid file.cpp:7: error: typedef name may not be a nested-name-specifier And the offending part of the file: template <class R, class C, class T0=void, class T1=void, class T2=void> struct MemberWrap; template <class R, class C, class T0> struct MemberWrap<R, C, T0>{ typedef R (C::*member_t)(T0); typedef typename boost::add_reference<typename T0>::type> TC0; // <---- offending line MemberWrap(member_t f) : m_wrapped(f){ } R operator()(C* p, TC0 p0){ GILRelease guard; return (p->*(this->m_wrapped))(p0); } member_t m_wrapped; };

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