WinUI UI Bugs

Common Symptoms

Symptom	Likely cause	Fix
Dialog crashes or never appears	Missing `XamlRoot`	Set `dialog.XamlRoot = this.Content.XamlRoot`
UI update from background fails	UWP dispatcher pattern or wrong thread	Use `DispatcherQueue.TryEnqueue`
Window APIs are null	UWP `Window.Current` or `CoreWindow` assumption	Track the window explicitly and use `AppWindow`
Title bar drag broken	Custom title bar hit testing/DPI not handled	Recheck title bar docs and test scaling
Theme/resource not found	Resource dictionary or namespace mismatch	Check `Microsoft.UI.Xaml` resource references

Search For Stale APIs

rg "Windows\.UI\.Xaml|CoreDispatcher|Window\.Current|ApplicationView|CoreWindow|MessageDialog"

Dialog Fix

var dialog = new ContentDialog
{
    Title = "Saved",
    Content = "Your changes were saved.",
    CloseButtonText = "OK",
    XamlRoot = this.Content.XamlRoot,
};
await dialog.ShowAsync();