Global exception handling

[AmSmart]

With the new host model in .NET Maui, will we get a straightforward way of catching exceptions?

[Flaflo]

I have the same question and I cannot find any solution.

[hartez]

With the new host model in .NET Maui, will we get a straightforward way of catching exceptions?

What sort of thing are you looking for? How would you like it to behave when exceptions occur?

[AmSmart]

@hartez, In other .NET applications, especially ASP.NET Core, we can set up a catch-all such that expectations that weren't anticipated can be handled at a general level to keep applications from crashing unexpectedly. This is the behaviour being described.

[Strypper]

@hartez, In other .NET applications, especially ASP.NET Core, we can set up a catch-all such that expectations that weren't anticipated can be handled at a general level to keep applications from crashing unexpectedly. This is the behaviour being described.

I think he left the chat 🤣🤣

[ThomasArdal]

Storing errors to a remote logging service would be a common use-case already commonly used on Xamarin and similar products.

[TanayParikh]

Cross linking dotnet/aspnetcore#40765 which handles the case of WPF/WinForms in Blazor Hybrid. If there's a canonical way to do global exception handling (like we have in WinForms/WPF), we need to ensure .NET MAUI Blazor Hybrid is able to integrate with it directly.

WPF/WinForms:

AppDomain.CurrentDomain.UnhandledException += (sender, error) =>
{
    MessageBox.Show(text: error.ExceptionObject.ToString(), caption: "Error");
};

cc/ @hartez

[janseris]

@mattleibow any progress on global exception handler?

[MJSanfelippo]

@mattleibow any update?

[viniciusverasdossantos]

:(

[harrykontopoulos]

It would be nice to have the equivalent of this: https://learn.microsoft.com/en-us/dotnet/api/system.windows.application.dispatcherunhandledexception?view=windowsdesktop-7.0

For common exceptions like a HttpRequestException it feels redundant to add try and catch all over the code. Similarly, on Asp.Net we don't kill the process every time a request results in an unhandled exception. Also, it would prevent shutting down the UI thread unnecessarily and just let the user know.

[egvijayanand]

Tried this, but no response.

[SmartmanApps]

Took me a long time to find this out, but this (or your own variation) will catch all exceptions (including the ones thrown by Xamarin which normally go un-noticed ;-) ). I haven't tried this in MAUI yet,, but I presume it'll work there too.

public App()
{
AppDomain.CurrentDomain.FirstChanceException+=CurrentDomain_FirstChanceException;
...
}

private void CurrentDomain_FirstChanceException(object sender, System.Runtime.ExceptionServices.FirstChanceExceptionEventArgs e)
{
System.Diagnostics.Debug.WriteLine($"********************************** UNHANDLED EXCEPTION! Details: {e.Exception.ToString()}");
}

[nogginbox]

I've not tested it thoroughly, but it is catching lots of exceptions including ones that are not causing obvious app issues.

Here is the output from starting my app up. The exception messages logged by this method are preceded with 'Before Handled':

Exception thrown: 'System.ArgumentException' in WinRT.Runtime.dll
Before Handled - Error: System.ArgumentException: Source object type is not a projected type and does not inherit from a projected type. (Parameter 'value')
   at WinRT.CastExtensions.GetRefForObject(Object value)

Exception thrown: 'System.DllNotFoundException' in System.Private.CoreLib.dll
Before Handled - Error: System.DllNotFoundException: Unable to load DLL 'Microsoft.Graphics.Canvas.Text.dll' or one of its dependencies: The specified module could not be found. (0x8007007E)
   at System.Runtime.InteropServices.NativeLibrary.LoadByName(String libraryName, QCallAssembly callingAssembly, Boolean hasDllImportSearchPathFlag, UInt32 dllImportSearchPathFlag, Boolean throwOnError)

Exception thrown: 'System.Runtime.InteropServices.COMException' in System.Private.CoreLib.dll
Before Handled - Error: System.Runtime.InteropServices.COMException (0x80070000): The operation completed successfully. (0x80070000)
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)

Exception thrown: 'System.IO.FileNotFoundException' in System.Private.CoreLib.dll
Before Handled - Error: System.IO.FileNotFoundException: Element not found.
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)

[TanayParikh]

Will the FirstChanceException event catch any exceptions not logged through Microsoft.Extensions.Logging?

From my (limited) testing, it appears to be the case.

Issue with this approach is it's a "firehose" of exceptions, as @nogginbox mentioned "it is catching lots of exceptions including ones that are not causing obvious app issues". This may work as an interim solution, but ideally we can integrate with AppDomain.CurrentDomain.UnhandledException to ensure we only catch critical exceptions.

Per the docs, the FirstChanceException "Occurs when an exception is thrown in managed code, before the runtime searches the call stack for an exception handler in the application domain.". Source.

[ThomasArdal]

It sounds a bit crazy to me that Maui supports both Microsoft.Extensions.Logging and events like FirstChanceException and UnhandledException and then don't log all exceptions through Microsoft.Extensions.Logging. If Microsoft.Extensions.Logging is supported in the first place, the events should not be intended for logging but other features like showing error messages to the user or similar. If we still need to subscribe to both events and logging to log all errors, the clever thing about having a logging framework in the mix goes away (IMO).

I think it's fine that Maui logs exceptions when they happen. But if they are not routed through the logging framework, it's way harder to filter out un-interesting exceptions like we can do with namespace filtering and similar in Microsoft.Extensions.Logging.

[JayMansel]

Just tested within MAUI and works beautifully :) Should definitely be the selected answer (go on OP :P)

[mattjohnsonpint]

You probably don't want to log the firehose that is first chance exceptions. First chance means immediately after throwing, even if it's caught and handled.

Take a look here for a better solution.

#653 (comment)

[mattjohnsonpint]

In putting together Sentry error monitoring for .NET MAUI, we've faced this head-on.

There are several different issues to deal with, as each platform that MAUI supports has its own quirks.

Here's a class you can use in your own code that provides a global event handler that works on all major platforms. (I didn't test Tizen.)
https://gist.github.com/mattjohnsonpint/7b385b7a2da7059c4a16562bc5ddb3b7

Usage:

MauiExceptions.UnhandledException += (sender, args) => { /* your code */ }

(If you decide to use Sentry, this is built-in.)

[MauriceChocoSwiss]

I've tried to use it, but I didn't find where to place it. I've placed it in the CreateMauiApp function but it didn't trigger when I throw Exception from iOS.

Can you tell me where I need to use it ?

[headintheclouds21]

I've also tried this for MacCatalyst and was unable to trigger it when I'm throwing an Exception.

Could you advise on where to use it in the application?

[anpin]

we are porting our app from XF to MAUI and we are using Sentry. Original app had catchers implemented in the same way as the gist. However MAUI version on iOS crashes in ApplyRelativeSourceBininding without catching anything or logging it to Sentry.

[MauriceChocoSwiss]

Any news ?
I've tested the solutions I've found here but it's not exactly what I want to do.

I would like to do like in Flutter (https://docs.flutter.dev/testing/errors) and catch all kind of exceptions (even customs I've made) and display them in Error page but the solutions I've found here doesn't help me to do that.

[7702244]

It works for me:
https://gist.github.com/mattjohnsonpint/7b385b7a2da7059c4a16562bc5ddb3b7

This is good for logging, but will not stop the application from crashing.

[ooleglysiak]

It works for me:
https://gist.github.com/mattjohnsonpint/7b385b7a2da7059c4a16562bc5ddb3b7

This is good for logging, but will not stop the application from crashing.

You can use the same methods as in Xamarin(Example:https://peterno.wordpress.com/2015/04/15/unhandled-exception-handling-in-ios-and-android-with-xamarin/)

[MauriceChocoSwiss]

I do these in each project main CS file and I've access to Handled property to set to true and prevent the app from crashing.

@ooleglysiak , with the link you shared, the guy only explain how to catch and log but not how to prevent app from crashing.

[ooleglysiak]

Sorry, sent the wrong link, didn't notice

[MauriceChocoSwiss]

I didn't get it work with iOS... I can't prevent app from crashing instead of showing a little snack to tell me something append... It's insane to crash the app when a api call return an exception (didn't find a way to catch all my api calls without puting try/catch arround each) or for example, when I lost internet connection and custom exception I want to throw

[viniciusverasdossantos]

Has anyone got a solution to prevent the application from closing when an exception occurs?

[MauriceChocoSwiss]

.Net 7, you need to add it to the App method, before the initialize

[headintheclouds21]

Any idea how to do this on MacCatalyst with .NET 7?

[MauriceChocoSwiss]

My project doesn't include MacCatalyst. You need to look at MacOS documentation to know if it's like on iOS (if unhandled exception is throwned, crash the app)

[Strypper]

Thanks you I but I my poup service in sitting at MAUI application, can't invoke the service from Platform specific

[janseris]

Thanks you I but I my poup service in sitting at MAUI application, can't invoke the service from Platform specific

Create a service through which you will Invoke the popup and inject it into the platform code

[SmartmanApps]

Thanks @TanayParikh and @mattjohnsonpint, I didn't know about UnhandledException - that'll teach me to read through ALL the Intellisense options when I'm trying something new! :-)

[MJSanfelippo]

Any updates on this? None of the given solutions work incredibly well, or only work in some scenarios/platforms. This seems like a super important feature to have for such a high-profile platform, but there seems to be no straight-forward way of doing it.

[Xyncgas]

how do you catch stackoverflow

[Xyncgas]

Although, if there's some sort of 'main' entry to your application, can't you just put try catch around it

[viniciusverasdossantos]

In maui .net 8 was there any solution? :(

[Strypper]

LOL

[rf-0]

Also interested.

[plppp2001]

Yeah me too...

[Dumuzy]

Anything new about the global exception handler? Such a thing is clearly needed. The XAML interpreter e.g. crashes under some circumstances in release mode but not in debug with the exactly same code. How could we debug this stuff? Best would be a catch all exception handler with which we could log the exception.

[CfmHansVallee]

Any update on this?
I am using Maui with net8, the code works fine, but the app still crashes, really looking forward to a true global exception handling pattern.

[VagnerVit]

I am trying to catch ObjectDisposedException which causes the whole app to crash and I think it causes the image disposing... I really cannot modify the base MAUI Image component.

Any updates?

[developer9969]

Hi just to say that this would be a dream in Maui land but sorry to be cynical but will never happen.

[pme442]

Any updates on this yet??

[janseris]

They don't react to discussions

[FreakyAli]

For an app targetting iOS and Android this should be more than enough:

public static class GlobalExceptionHandler
{
    // We'll route all unhandled exceptions through this one event.
    public static event UnhandledExceptionEventHandler UnhandledException;

    static GlobalExceptionHandler()
    {
        AppDomain.CurrentDomain.UnhandledException += (sender, args) =>
        {
            UnhandledException?.Invoke(sender, args);
        };

        // Events fired by the TaskScheduler. That is calls like Task.Run(...)     
        TaskScheduler.UnobservedTaskException += (sender, args) =>
        {
            UnhandledException?.Invoke(sender, new UnhandledExceptionEventArgs(args.Exception, false));
        };

#if IOS

        // For iOS and Mac Catalyst
        // Exceptions will flow through AppDomain.CurrentDomain.UnhandledException,
        // but we need to set UnwindNativeCode to get it to work correctly. 
        // 
        // See: https://github.com/xamarin/xamarin-macios/issues/15252
        
        ObjCRuntime.Runtime.MarshalManagedException += (_, args) =>
        {
            args.ExceptionMode = ObjCRuntime.MarshalManagedExceptionMode.UnwindNativeCode;
        };

#elif ANDROID

        // For Android:
        // All exceptions will flow through Android.Runtime.AndroidEnvironment.UnhandledExceptionRaiser,
        // and NOT through AppDomain.CurrentDomain.UnhandledException

        Android.Runtime.AndroidEnvironment.UnhandledExceptionRaiser += (sender, args) =>
        {
            args.Handled = true;
            UnhandledException?.Invoke(sender, new UnhandledExceptionEventArgs(args.Exception, true));
        };

        Java.Lang.Thread.DefaultUncaughtExceptionHandler = new CustomUncaughtExceptionHandler(e =>
            UnhandledException?.Invoke(null, new UnhandledExceptionEventArgs(e, true)));
#endif
    }
}

#if ANDROID
public class CustomUncaughtExceptionHandler(Action<Java.Lang.Throwable> callback)
    : Java.Lang.Object, Java.Lang.Thread.IUncaughtExceptionHandler
{
    public void UncaughtException(Java.Lang.Thread t, Java.Lang.Throwable e)
    {
        callback(e);
    }
}
#endif

And a simple way to use this would be:

GlobalExceptionHandler.UnhandledException += GlobalExceptionHandler_UnhandledException;

 private void GlobalExceptionHandler_UnhandledException(object sender, UnhandledExceptionEventArgs e)
  {
      var exception = e.ExceptionObject as System.Exception;
      // Log this exception or whatever
  }

[ThomasArdal]

Isn't this the same as MauiExceptions or did you optimize something?

[FreakyAli]

It has TaskScheduler.UnobservedTaskException and native Android uncaught thread exceptions so I guess it gets you a bit more