[android] improve performance of ActivityExtensions.GetWindowFrame

[jonathanpeppers]

I've been working to get back some of our lost startup performance on Android in .NET MAUI. We are really close, a few changes will get .NET 8 on par or faster than .NET 7.

Profiling startup of a dotnet new maui app on a Pixel 5, dotnet-trace reported time spent in:

20.05ms (0.73%)	0.22ns (<0.01%)	microsoft.maui!Microsoft.Maui.Platform.ActivityExtensions.GetWindowFrame(Android.App.Activity)

What is particularly interesting here, is this method is called multiple times on startup:

• X
• Y
• Width
• Height
• WindowHandler.ConnectHandler()

In the future, we should come up with a way the PropertyMapper can somehow "collapse" these calls so we can do it once.

For now, however, I took the following C# code that looks to do 3 Java interop calls:

internal static Rect GetWindowFrame(this Android.App.Activity activity)
{
    var wmc = WindowMetricsCalculator.Companion.OrCreate;
    var wm = wmc.ComputeCurrentWindowMetrics(activity);
    var bounds = wm.Bounds;
    return activity.FromPixels(bounds);
}

And moved to Java, so we now have 1:

@NonNull
public static Rect getCurrentWindowMetrics(Activity activity) {
    return WindowMetricsCalculator.Companion
        .getOrCreate()
        .computeCurrentWindowMetrics(activity)
        .getBounds();
}

The result being:

Before:
20.05ms (0.73%)	0.22ns (<0.01%)	microsoft.maui!Microsoft.Maui.Platform.ActivityExtensions.GetWindowFrame(Android.App.Activity)
After:
11.94ms (0.22%)	0.06ns (<0.01%)	microsoft.maui!Microsoft.Maui.Platform.ActivityExtensions.GetWindowFrame(Android.App.Activity)

I'd estimate this might improve startup by ~8ms.

In future .NET releases, we should revisit the PropertyMapper pattern. This could be even better if it was only called once.

[jonathanpeppers]

It is OK to add this dependency in Java, because we already have it in C#:

maui/eng/AndroidX.targets

Lines 60 to 63 in 8203e4d

	<PackageReference
	Update="Xamarin.AndroidX.Window.WindowJava"
	Version="1.1.0.1"
	/>

We were using the same APIs in C# previously.

[rmarinho]

Don't we batch these updates? or was this before? only on Xamarin.Forms?

[jonathanpeppers]

This is actually the example:

https://github.com/dotnet/maui/blob/main/src/Core/src/Platform/Android/ActivityExtensions.cs

You can see how all these methods would call GetWindowFrame() over and over.

This pattern is all over MAUI, so ideally something to think about in the future.

[rmarinho]

This is actually the example:

https://github.com/dotnet/maui/blob/main/src/Core/src/Platform/Android/ActivityExtensions.cs

You can see how all these methods would call GetWindowFrame() over and over.

This pattern is all over MAUI, so ideally something to think about in the future.

Can you please create a issue that we track this as a improvement for net9 ?

[jonathanpeppers]

The issue is: #17303