Troubleshooting tips for developing on macOS

[daltzctr]

Hey folks. I have a complex MAUI application that targets pretty much every platform MAUI supports with primary targets being Windows and macOS/macCatalyst, and secondary targets Android and iOS.

In most cases, I rarely see issues when developing on Windows. However, macOS is it's own special sort of beast. For example, on macOS

• Having a debugger attached will cause the application to freeze after a period of time (I believe it gets exaggerated the more complex views are shown)
  • If the debugger is not attached, there are no issues
• Exceptions are almost always in the form of native segfaults and very difficult to debug, even with debug symbols and "Just My Code" disabled
• When I do get exceptions, their stacktrace is trimmed to only include the most recent stack (aka an exception in UIApplication... which isn't useful)
• Sourcelink/step into source is not functional
  • e.g. I can Ctrl + Click into the VisualElement implementation for Loaded, but I am unable to set breakpoints

Here's an example exception I'm currently facing after updating MAUI (.NET 9 9.0.60) and performing a shell navigation

An unhandled exception of type 'System.InvalidOperationException' occurred in Microsoft.MacCatalyst.dll: 'Handler is not set on element'
   at UIKit.UIApplication.xamarin_UIApplicationMain(Int32 argc, IntPtr argv, IntPtr principalClassName, IntPtr delegateClassName, IntPtr* gchandle)
   at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in /Users/builder/azdo/_work/9/s/xamarin-macios/src/UIKit/UIApplication.cs:line 65
   at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in /Users/builder/azdo/_work/9/s/xamarin-macios/src/UIKit/UIApplication.cs:line 97
   at myprogram.Main(String[] args) in /Users/myuser/Desktop/myprogram/Platforms/MacCatalyst/Program.cs:line 14

The exception is stuck in UIApplication with the InnerException being null. However, a separate printout to the console does tell me my exception is happening somewhere in Loaded due to a missing Handler

11:57:27 FTL] Stacktrace:
    at Microsoft.Maui.Platform.ViewExtensions.OnLoaded(IElement element, Action action)
   at Microsoft.Maui.Controls.VisualElement.HandlePlatformUnloadedLoaded()
   at Microsoft.Maui.Controls.VisualElement.UpdatePlatformUnloadedLoadedWiring(Window newWindow, Window oldWindow)
   at Microsoft.Maui.Controls.VisualElement.remove_Loaded(EventHandler value)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellPageRendererTracker.Dispose(Boolean disposing)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellPageRendererTracker.Dispose()
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.DisposePage(Page page, Boolean calledFromDispose)
   at Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.OnPopRequested(NavigationRequestedEventArgs e)
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_0(Object state)
   at Foundation.NSAsyncSynchronizationContextDispatcher.Apply() in /Users/builder/azdo/_work/9/s/xamarin-macios/src/Foundation/NSAction.cs:line 179
--- End of stack trace from previous location ---

Okay. It's trying to dispose of the page and is failing to unload it because the Page handler seems to be missing? Why? Let's break point in ViewExtensions.OnLoaded. Oh... that doesn't work in VS Code (breakpoint says the module isn't loaded even though "Just My Code" is disabled).

So my question to the community how you debug issues like this on macOS

• How do you debug weird exceptions like this?
• How do you debug deadlocks or freezes?

[daltzctr]

Tried out Rider to see if it would be any more useful and...