C# .NET Exception : AppDomain.UnhandledException

When an unhandled exception is manifested in a Console application, the AppDomain .UnhandledException is raised. Subscribe to the event to clean up the resources of the application, such as closing files and relinquishing data connections. You might also record the unhandled exception in the event log or another location. It is important to note that the exception is not caught in the AppDomain.UnhandledException handler. After the handler finishes, the unhandled exception causes the application to be terminated. The AppDomain.UnhandledException event is triggered only in the initial application domain; it is ignored in other application domains.

Subscribe to the AppDomain.UnhandledException event with an UnhandledExceptionEventHandler delegate. The delegate has two parameters. The object parameter is the AppDomain object of the initial application domain. The UnhandledExceptionEventArgs parameter contains the specifics of the unhandled exception. This is the syntax of the UnhandledExceptionEventHandler:

UnhandledExceptionEventHandler syntax:

• void UnhandledExceptionEventHandler(object sender, UnhandledExceptionEventArgs e)

UnhandledExceptionEventArgs offers the IsTerminating and ExceptionObject properties. IsTerminating is a Boolean property indicating the status of the application. If true, the application is terminating because of the exception. If false, the application survives the exception. In .NET 2.0, this property is always true. Unhandled exceptions on both managed and unmanaged threads terminate an application. This is cleaner than the .NET 1.1 unhandled exception model, where exceptions raised on managed threads were nonfatal. The Exception property is an exception object for the unhandled exception. Inexplicably, this property is an object type, not an Exception type. Cast the property to the Exception type to access the details of the exception.

In the following Console application, the OnUnhandledException method is added to the AppDomain.UnhandledException event. When the subsequent divide by zero exception occurs, the OnUnhandledException method is called.

using System;

namespace Examples.Exceptions
{
    public class Program
    {
        public static void Main()
        {
            AppDomain.CurrentDomain.UnhandledException +=
                new UnhandledExceptionEventHandler(
                    OnUnhandledException);

            int vara = 5, varb = 0;
            vara /= varb;

            Console.ReadKey();
        }

        public static void OnUnhandledException(object sender, UnhandledExceptionEventArgs e)
        {
            string application_name = sender.ToString();
            Exception except = (Exception)e.ExceptionObject;
            string errormessage = "Application " + application_name + " [ Exception " + except.Message + " ]";
            Console.WriteLine(errormessage);
        }
    }
}