C# Winforms handle unhandled exceptions

Question

I want to catch all unhandled exceptions in my application. so I used this code to catch all the unhandled exceptions:

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.ThreadException += new ThreadExceptionEventHandler(Application_ThreadException);
        AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
    }

    static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
    {
        SaveEx(e.Exception);
        Application.Exit();
    }

    static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        SaveEx((Exception)e.ExceptionObject);
        Application.Exit();
    }

    static void SaveEx(Exception ex)
    {
        bool exists = System.IO.Directory.Exists(Path.GetDirectoryName(@"C:\AppLogs\"));

        if (!exists)
            System.IO.Directory.CreateDirectory(Path.GetDirectoryName(@"C:\AppLogs\"));


        String filePath = @"C:\AppLogs\" + DateTime.Now.ToString("yyyy-dd-M--HH-mm-ss") + ".txt";

        String log = "===========Start=============\r\n";

        log += "Error Message: " + ex.Message + "\r\n";
        log += "Stack Trace: " + ex.StackTrace + "\r\n";

        log += "===========End=============";

        System.IO.File.WriteAllText(filePath, log);
    }
}

I tried to raise these exceptions with a divide in 0:

on main thread it's work perfect:

int t = 0;
int r = 5 / t;

But when i try to do it inside a Thread:

 Thread thread = new Thread(delegate()
 {
      int t = 0;
      int r = 5 / t;
 });
 thread.Start();

The CurrentDomain_UnhandledException function got called but it keeps calling the int r = 5 / t; row in my code so I have a loop of exceptions. Any idea what can be the problem? the thread is called only once.

Answer 1

You need to change Application UnhandledExceptionMode to UnhandledExceptionMode.CatchException to make things works correctly. Microsoft already wrote a very good article about it here.

I tried to simulate your work. Everything worked well, take a look on my example.

    [STAThread]
    static void Main()
    {
        // Set the unhandled exception mode to force all Windows Forms errors to go through
        // our handler.
        Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);

        // Add the event handler for handling UI thread exceptions to the event.
        Application.ThreadException += Application_ThreadException;

        // Add the event handler for handling non-UI thread exceptions to the event. 
        AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
    }

    private static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
    {
        MessageBox.Show(e.Exception.Message, "Application_ThreadException");
        Application.Exit();
    }

    private static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        var exception = e.ExceptionObject as Exception;
        MessageBox.Show(exception.Message, "CurrentDomain_UnhandledException");
        Application.Exit();
    }

So, if we raise an exception inside a thread like below:

    private void button1_Click(object sender, EventArgs e)
    {
        var thread = new Thread(delegate () {
            throw new DivideByZeroException();
        });

        thread.Start();
    }

1. button1_Click is fired.
2. thread get started and raises a DividedByZeroException.
3. CurrentDomain_UnhandledException catches the exception, shows the message and closes the app