Evaluate throwing if Window is null on UWP

[jamesmontemagno]

Should we be throwing here?

Essentials/Xamarin.Essentials/MainThread/MainThread.uwp.cs

Line 16 in f56c8ba

if (dispatcher == null)

• Check if there is a main window, if not run on current thread
• Audit usage of any Platform main thread usage and change to shared

[Redth]

We should instead check if there IS a main window, and if there isn't we are already on the 'main' thread and can just execute on the current thread.

[tipa]

It can still crash here:

Essentials/Xamarin.Essentials/MainThread/MainThread.uwp.cs

Line 16 in b018723

if (CoreApplication.MainView.CoreWindow == null)

For example, when execute too early, before the main window has been created, for example in the App constructor

[jamesmontemagno]

Do you want to do a PR? or do you want me to?

[tipa]

I am failing to get the project running without errors on my machine :(
What I would do is wrap line 16 in a try-catch and return true if the InvalidOperationException is thrown

[jamesmontemagno]

No worries (We recommend VS 2017 as there is a regression on VS 2019 16.1 right now for the multi-targeting stuff we are using). I put in a PR #803 to fix it up.

[tipa]

I think if the issue hasn't been fixed with your PR, as the InvalidOperationException can still be thrown, which happens when you access the MainView property before it has been created (try call MainThread.BeginInvokeOnMainThread(action) in your apps constructor to reproduce)

[tipa]

@jamesmontemagno should I open a new issue regarding this problem?

[jamesmontemagno]

It should never throw as we always call IsMainThread and if CoreWindow is null then we return true so it should just fire.

If you can open with a repro that would be good. Or send down a PR :)

[tipa]

Opened a new issue here: #1020