CODEWITHSUNDEEP
c#winformsnumericupdown
Rahul Vasantrao Kamble
Rahul Vasantrao Kamble

Reputation: 251

Exception swallow in WinForm Application c#

public partial class Form1 : Form
    {
        public class abc
        {
            public static decimal Divide(int a,int b)
            {
                return a / b;
            }
        }
        public Form1()
        {
            InitializeComponent();
            numericUpDown1.ValueChanged += NumericUpDown1_ValueChanged;
            numericUpDown1.Controls[1].Leave += Form1_Leave;
        }

        private void Form1_Leave(object sender, EventArgs e)
        {
            //abc.Divide(15, 0);
        }

        private void NumericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            abc.Divide(15, 0);
        }
    }

And Program.cs is haveing catch block as follow

static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.ThreadException += Application_ThreadException;
            try
            {
                Application.Run(new Form1());
            }
            catch
            {
                MessageBox.Show("Exception Hadled");
            }
        }

        private static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e)
        {
            MessageBox.Show("Exception Hadnled");
        }
    }

In Above sample, no message box is triggered. But if I use leave event catch executes. Why ValueChanged event is not Prapogating exception to outer world?

Upvotes: 2

Views: 168

Answers (2)

Oguz Ozgul
Oguz Ozgul

Reputation: 7187

It is not, and this is by design. Don't have try/catch around Application.Run().

your Form_Leave event handler should also has the same behavior.

When you start your program with Application.Run(), it starts a message loop and creates a ThreadContext and ApplicationContext.

The message loop handles window messages sent to the active form (let's say the Tab key-press when on the numeric control) and executes required actions.

This is what handles the exception when you first get it:

internal void UpdateFocusedControl() in ContainerControl:

try {
    leaveControl.NotifyLeave();
}
catch (Exception e) {
    Application.OnThreadException(e);
}

Now OnThreadException calls your Application_ThreadException.

Let's try to throw again here.

private static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e)
{
    MessageBox.Show("Exception Handled");
    throw e.Exception;
}

Next time, the exception is handled by the ThreadContext

internal bool PreTranslateMessage(ref NativeMethods.MSG msg) in Application+ThreadContext

try
{
    // Message processing, like leave control and focus next and call event handlers
}
catch (Exception e)
{
    OnThreadException(e);
}

And finally, when you re-throw, this time your catch statement is activated.

Hope this clarifies things on your side.

Upvotes: 1

Aamer Khawaja
Aamer Khawaja

Reputation: 17

Change your code to this:

 try
        {
            Application.Run(new Form1());
        }
        catch (Exception)
        {
            MessageBox.Show("Exception Hadled");
        }

Upvotes: 0

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