Unhandled exception on popup open

Describe the bug

Such a code causes an unhandled exception

Steps to reproduce the bug

1. Create a blank WinUI app for desktop
2. Add the following code in MainWindow constructor after InitializeComponent.

        var p = new Popup();
        p.Child = new TextBlock() { Text = "Text" };
        p.IsOpen = true;

1. Run application

Version Info

Windows 10 1903 (OS Build 18362.1082)

NuGet package version:

WinUI 3.0.0-preview2.200713.0

Windows app type:

UWP	Win32
	Yes

Device form factor	Saw the problem?
Desktop	Yes

[codendone]

The error message shown in the output window is “explaining” the error, but we should definitely make some improvements to better expose the error (rather than just seeing the E_UNEXPECTED message in the exception dialog), better explain what needs to be done, and better document this issue.

The problem is that this is a parentless popup, so XAML doesn’t know which window to show the popup for. (And it complains even when there is only one to prevent weird behavior of having code stop working when there is more than one window.) There are two possible fixes to this: (1) add the Popup in the Children list of some other element, or (2) set the XamlRoot property to explicitly state what the popup belongs to.

Option (2) provides a trivial fix in your example by adding the second line here:

            var p = new Popup();
            p.XamlRoot = this.Content.XamlRoot;
            p.Child = new TextBlock() { Text = "Popup Text" };
            p.IsOpen = true;

Note: The XamlRoot needs to be set before setting the popup to IsOpen=true.

[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.