DialogHost IsLoaded but not exactly

Bug explanation

I've uploaded a sample project illustrating the issue.

When trying to get a WPF window to open a view using DialogHost on initial startup/show, I noticed that the DialogHost.Show method throws an exception even though the DialogHost instance IsLoaded property was true. I am thinking the DialogHost is loaded but not yet registered in the LoadedInstances HashSet by the time the Window.IsLoaded event triggers.

https://github.com/jbooth88/DialogHostStartupExample

Looks like IsLoaded property is coming from FrameworkElement, so my guess here is that it's not the correct value to identify whether or not the DialogHost is fully initialized. I am not sure of the best way to solve this problem.

Version

5.2.1

Bắt đầu bằng cách tái hiện chuỗi khởi động với project DialogHostStartupExample được liên kết và kiểm tra DialogHost.Show, FrameworkElement.IsLoaded cùng LoadedInstances HashSet. Xác định lý do Show có thể chạy trước khi việc đăng ký hoàn tất, sau đó xác minh fix với kịch bản mở cửa sổ/view ban đầu được mô tả trong issue.