[UWP] Fixes for font when using MultiWindow

[rmarinho]

Description of Change

When using multiple windows we need to take in account that each CoreApplicationView has it's own thread so caching items doesn't work if they are shared. Like FontFamilies for example

We also need to relayout our contents when the window is resized.

Issues Resolved

• fixes [Bug] [UWP] Setting the FontFamily crashes a multi-window app #11705

API Changes

None

Platforms Affected

• UWP

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Try open 2 our 3 windows from the control gallery

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[KPixel]

Regarding the fix for resizing secondary windows, my suggestion was a workaround.

Can you please investigate why that is not an issue for the main window? I would think that they should be resized in the same way.

[KPixel]

@rmarinho @hartez Please, only commit the fix for FontExtensions.

The issue with resizing windows should be investigated first...

[hartez]

Split up this fix and the resizing one.

[hartez]

@KPixel makes a good point - why does this work? We should pull this out and create a separate issue.

[rmarinho]

Ok i removed that code.. Also another code that works is something like this bellow. But we don't want to create a new Window right?

public class NewSecondaryWindowsPage : WindowsPage
{
	protected override void OnNavigatedTo(Windows.UI.Xaml.Navigation.NavigationEventArgs e)
	{
		var pageType = e.Parameter as Type;
		ContentPage instance = (ContentPage)Activator.CreateInstance(pageType);
		RegisterWindow(instance);
		base.OnNavigatedTo(e);
	}
}

public async Task OpenSecondaryWindow(Type pageType)
{
	CoreApplicationView newView = CoreApplication.CreateNewView();
	int newViewId = 0;
	await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
	{
		var frame = new Windows.UI.Xaml.Controls.Frame();
		Window.Current.Content = frame;
		frame.Navigate(typeof(NewSecondaryWindowsPage), pageType);
		Window.Current.Activate();
		newViewId = ApplicationView.GetForCurrentView().Id;
	});
	bool viewShown = await ApplicationViewSwitcher.TryShowAsStandaloneAsync(newViewId);
}

[KPixel]

Interesting. I think this points to the root of the issue: Application.MainPage...
I would like to create a new issue to discuss a solution there. Ok?

[rmarinho]

Yeah the issue from what i understand is here :

Xamarin.Forms/Xamarin.Forms.Platform.UAP/PageExtensions.cs

Line 58 in 719fc7a

var root = new Windows.UI.Xaml.Controls.Page();

We create a page just to fake it as "root" and so the code that listens to size changes here:

Xamarin.Forms/Xamarin.Forms.Platform.UAP/Platform.cs

Line 91 in 3ca1250

_container.SizeChanged += OnRendererSizeChanged;

Doesn't work, because the _page (that we passed to the Platform) is not added to the VisualTree

[KPixel]

There is also the following code which expects all windows to have a specific structure:

Xamarin.Forms/Xamarin.Forms.Platform.UAP/Platform.cs

Lines 51 to 59 in 3ca1250

	internal static Platform Current
	{
	get
	{
	var frame = Window.Current?.Content as Windows.UI.Xaml.Controls.Frame;
	var wbp = frame?.Content as WindowsBasePage;
	return wbp?.Platform;
	}
	}

So, your code above seems like the expected way to initialize a secondary window.

I've updated my app to follow this approach, and it works.

[KPixel]

This means that the "fix" for the resize issue is to update OpenSecondaryWindow() in the Control Gallery app.

Also, the PageExtensions class was a trap. From what I can see, in this entire repo, it is used in two scenarios:

1. For FormsEmbeddedPageWrapper pages (and there is no sample/test for that).
2. For the UWP version of DualScreen. And I think that code should be updated to follow the WindowsPage approach, otherwise, it will suffer from the same resize bug.

[KPixel]

Let's ship this fix! :)

[KPixel]

Hello,

Can we please merge this simple fix before 5.0?

It is ready to go!