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I have read these two pages from msdn: 1, 2

So I constructed this simple Web Forms app:

public partial class Form1 : Form { public Form1() { InitializeComponent(); new Thread(new ThreadStart(throwException)).Start(); } public static void throwException() { throw new Exception(); } public static void UnhandledExHandler(object sender, UnhandledExceptionEventArgs t) { MessageBox.Show("This is exception is unhandled."); } } static class Program { static void Main() { Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException); AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(Form1.UnhandledExHandler); Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } }

The problem with this is that after executing UnhandledExHandler, Forms1() constructor does not return but keeps throwing Exception, I mean it keeps calling throwException() on a new thread. The end user experience popping of MessageBox continuously. I know I must call Application.Exit() inside UnhandledExHandler to exit the app. But shouldnt this stop calling UnhandledExHandler after called once?

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Assuming that all of your projects are running in the same appdomain, this will work correctly. We have this exact code encapsulated in a common DLL that is shared among numerous applications.

An additional suggestion: if this is used in Windows Forms applications, you probably also want to add a handler for System.Windows.Forms.Application.ThreadException.

This serves as a backstop when, for example, someone forgets to add exception handling to a control event.

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My question if u think above should show MessageBox once, why it keeps showing again and again? Build simple Win Forms app and check the behavior
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If you run your app without debugging you will get a message box and your app will be closed. You see many msg boxes because of the debugger work.

Your UnhandledExceptionEventArgs.IsTerminating is true, I guess you will not able to do anything with it in CurrentDomain.UnhandledException handler.

But you can handle it in ThreadException event handler.

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Yes I checked the behavior out of VS, I run it by double clicking exe in Debug folder, so it showed a MessageBox then it displayed normal Program Stopped Working box and when I clicked Ok/Cancel the app was closed - is this desired or should it only return from UnhandledExHandler
In most cases your app will be unloaded (msdn.microsoft.com/ru-ru/library/…). You can try solution from this post: stackoverflow.com/questions/186854/…
I tested behavior after adding Application.Exit() and it still does not close silently after dismissal of MessageBox instead it shows Windows error message box saying This app stopped working...
This is working for me: Application.Exit(new CancelEventArgs(false));
I do also checked by adding new CancelEventArgs(false) to Application.Exit() after MessageBox it shows App Stopped Working...Check online...Close app Windows message.

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