Question

How to catch exception in the main thread if the exception occurs in the secondary thread?

The code snippet for the scenario is given below:

private void button1_Click(object sender, EventArgs e)
{
    try
    {
        Thread th1 = new Thread(new ThreadStart(Test));
        th1.Start();               
    }
    catch (Exception)
    { 

    }
}

void Test()
{
    for (int i = 0; i < 100; i++)
    {
        Thread.Sleep(100);

        if (i == 2)
            throw new MyException();
    }
}

Answer 1

You can add a Application.ThreadException Event handler:

Joe is correct. Given the above windows forms code I was assuming Windows forms:

This event allows your Windows Forms
application to handle otherwise
unhandled exceptions that occur in
Windows Forms threads. Attach your
event handlers to the ThreadException
event to deal with these exceptions,
which will leave your application in
an unknown state. Where possible,
exceptions should be handled by a
structured exception handling block.

See Unexpected Errors in Managed Applications