Exceptions catching / handling / throwing

UpdatedJune 6, 2022

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Exceptions catching / handling / throwing

Dominik Schischma

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Yet another developer journey ...

19 posts

Short introduction

When an exception is thrown, the following program code is not executed anymore (beside there is a finally block) until it is catched. If it is not catched somewhere, the program is terminated.

// we just want one method throwing the exception private void ExcSample() { throw Exception("foo"); } // public static void Main() { // will result in termination of the program as no exception will be catched ExcSample(); // will catch the exception in the catch block and write the message to console try { ExcSample(); } catch(Exception exc) { Console.WriteLine($"Error occured: {exc.Message}"); } // example with finally block try { ExcSample(); } catch(Exception exc) { Console.WriteLine($"Error occured: {exc.Message}"); } finally { // code here would be always executed: if an exception does occur or if not } // also possible, only finally try { ExcSample(); } finally { // code here would be always executed: if an exception does occur or if not } }

Custom or user-defined exceptions

Custom or user-defined exceptions are exceptions which have been created by yourself. The decision to create own exceptions may be due to additional requirements for the Exception itself (e. g. localization or for logic operations where no existing Exception may fit your needs.

Exceptions can be simply created by deriving your new Exception class from the base class or any other Exception class:

public class MyOwnException : Exception { public uint MyInternalErrorCode { get; set; } public MyOwnException(uint errorCode) { MyInternalErrorCode = errorCode; } /// <inheritdoc /> public MyOwnException(string? message) : base(message) { } public MyOwnException(string? message, uint myInternalErrorCode) : base(message) { MyInternalErrorCode = myInternalErrorCode; } /// <inheritdoc /> public MyOwnException(string? message, Exception? innerException) : base(message, innerException) { } public MyOwnException(string? message, Exception? innerException, uint myInternalErrorCode) : base(message, innerException) { MyInternalErrorCode = myInternalErrorCode; } }

Catching unhandled exceptions

To catch all unhandled exceptions in your program, e. g. for logging it to a file instead of default logging facilities it is possible to subscribe to some even:

static async Task Main(string[] args) { // subscribe to event for all unhandled eceptions AppDomain.CurrentDomain.UnhandledException += ApplicationUnhandledException; // rest of code... } // event handler private static void ApplicationUnhandledException(object sender, UnhandledExceptionEventArgs e) { // log the exception for example Logger.Fatal((Exception) e.ExceptionObject, "Unhandled exception: {0}", e.ExceptionObject); }

Using Tasks the above will not work, but the TaskScheduler class does provide an Event UnobservedTaskException which we can use in this case.

Credits

Command Palette