Centralised Exception Handling in C# Windows Application

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Introduction

You might have been come across a situation when you may need your application to Log all your application errors. This can be done using try catch blocks. But what about unhandled exceptions. When your application comes across an unhandled exception, your application will exit just showing an error window. This may sometimes result in loss of data. To avoid this, you need to handle all the unhandled exceptions from a centralized method. This article explains a simple way of centralized exception handling.

Using the Code

There are two sources where the exceptions are raised. Either the exception can be raised in the main thread or it can be raised in the additional threads used in the application. Let us now walk in to the code how to handle this. 

static class Program
{
    [STAThread]
    static void Main()
    {
        // Add handler to handle the exception raised by main threads
        Application.ThreadException += 
        new System.Threading.ThreadExceptionEventHandler(Application_ThreadException);
        
        // Add handler to handle the exception raised by additional threads
        AppDomain.CurrentDomain.UnhandledException += 
        new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
        
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
        
        // Stop the application and all the threads in suspended state.
        Environment.Exit(-1);            
    }
    
    static void Application_ThreadException
    	(object sender, System.Threading.ThreadExceptionEventArgs e)
    {// All exceptions thrown by the main thread are handled over this method
        
        ShowExceptionDetails(e.Exception);
    }
    
    static void CurrentDomain_UnhandledException
    	(object sender, UnhandledExceptionEventArgs e)
    {// All exceptions thrown by additional threads are handled in this method
        
        ShowExceptionDetails(e.ExceptionObject as Exception);
        
        // Suspend the current thread for now to stop the exception from throwing.
        Thread.CurrentThread.Suspend();
    }
    
    static void ShowExceptionDetails(Exception Ex)
    {
        // Do logging of exception details
        MessageBox.Show(Ex.Message, Ex.TargetSite.ToString(), 
        		MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

In the above class, we shall attach an event handler to two events. It is better to attach these events as soon as the main method starts.

Application.ThreadException - This event will be raised when an exception is thrown in the main thread. If we add an event handler, then the exception is handled over the method.

AppDomain.CurrentDomain.UnhandledException - This event will be raised when an exception is thrown in the additional threads used in the application. The worse scenario here is as soon as the handlers' execution gets over, the exception is again thrown whereas the application ends. This need to be handled. Here I have used a bit of code to handle this situation and continue the execution of the application without interruption.

The logic I have used to overcome this situation is just suspending the thread in the event handler, so that the application continues to work fine. Again a problem arises in suspending this thread. When the main form is closed, the application normally needs to exit, but as the thread is in suspended state, the application will still remain running. So to exit the application completely and stop the process, Environment.Exit(-1) must be called before the ending of the main method.

Points of Interest

This article enables you to handle any exceptions without forcing your application to end due to unhandled exceptions in any case.

History

• 20^th October, 2009: Initial post