[uwp] NullReferenceException, then XamlParseException: Cannot create instance of type...

Describe the bug

For some user control classes, I can’t create them in xaml, an error (actually two) gets thrown. at this.InitializeComponent()

For additional context, I get this error during startup:

Steps to reproduce the bug

This is a weird bug, and my app is really big, and it only happens on some user controls and not others, but I can’t figure out what separates the classes with the problem.

My MainPage looks like this:

My select_sound_effect_ctrl xaml looks like this:

At startup: First I get

Then I get

It basically says it can’t create an instance of type select_sound_effect_view_model, but I don’t understand why. It’s a public class, and as matter of fact, this works (just creating it in code):

Once again, if I leave the class as it originally is, and I create an instance in code-behind, it works:

Expected behavior

Clearly, the error shouldn’t happen. This occurs at random times, code that once worked, sometimes stops working after months. And sure, it’s rather simple to create a control in code every now and then, but what when it’s used in a more complicated scenario, like, have an ItemsControl of such items?

Windows 10 version	Saw the problem?
May 2020 Update (19041)	Yes

[andrewleader]

Thanks for filing this, since this is a XAML issue, transferring to the WinUI XAML repo.

[github-actions[bot]]

This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 5 days.