[android] improve performance of ImageHandler.PlatformArrange()

[jonathanpeppers]

Context: https://github.com/davidortinau/AllTheLists

Profiling @davidortinau's app, I noticed the "Check-ins" sample felt the slowest on Android.

One thing I noticed while scrolling:

98.75ms (0.90%) Microsoft.Maui!Microsoft.Maui.Handlers.ImageHandler.PlatformArrange(Microsoft.Maui.Graphics.Rect)
67.11ms (0.61%) Mono.Android!Android.Widget.ImageView.ScaleType.get_CenterCrop()

In this case, PlatformArrange() is called a lot for every <Image/>:

if (PlatformView.GetScaleType() == ImageView.ScaleType.CenterCrop)
{
    var (left, top, right, bottom) = PlatformView.Context!.ToPixels(frame);
    var clipRect = new Android.Graphics.Rect(0, 0, right - left, bottom - top);
    PlatformView.ClipBounds = clipRect;
}

ImageView.ScaleType is a class, and so and some bookkeeping is done to lookup the same C# instance for a Java object. We can make this a bit better by writing a new Java method:

public static boolean isImageViewCenterCrop(@NonNull ImageView imageView) {
    return imageView.getScaleType() == ImageView.ScaleType.CENTER_CROP;
}

Next, let's make a PlatformView.ToPixels() extension method that can avoid calling View.Context for the same reason.

Lastly, we can make a PlatformInterop.SetClipBounds() method to avoid creating a Android.Graphics.Rect object in C#.

With these changes, I can only see the topmost PlatformArrange() method now:

2.93ms (0.03%) Microsoft.Maui!Microsoft.Maui.Handlers.ImageHandler.PlatformArrange(Microsoft.Maui.Graphics.Rect)

This should improve the layout performance of all .NET MAUI <Image/> on Android. I also "banned" GetScaleType() in eng/BannedSymbols.txt.

[bcaceiro]

Is this going into next SR? Seems like a great adition!

[bcaceiro]

Any news on this?

[bcaceiro]

Sorry to bump this, but feels like this is an important MR to improve performance overall in a basic element like Image in all applications

[jonathanpeppers]

@bcaceiro I originally held off on this because it could be fixed here:

• [generator] Cache static final field values. java-interop#1248
• Java enumerations should *cache* the field values java-interop#1243

We'll try to merge it now, as those changes didn't land.

[Copilot]

Pull Request Overview

This PR improves the performance of ImageHandler.PlatformArrange() on Android by optimizing several expensive operations during image layout. The changes focus on reducing object allocations and method call overhead during frequent layout operations.

Key changes:

• Replaces expensive GetScaleType() calls with a native Java method that avoids C# object creation
• Introduces extension methods to avoid unnecessary View.Context property access
• Adds native Java methods to set clip bounds without creating Android.Graphics.Rect objects in C#

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Core/src/Handlers/Image/ImageHandler.Android.cs	Updates PlatformArrange() to use new optimized methods for scale type checking and clip bounds setting
src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformInterop.java	Adds native Java methods isImageViewCenterCrop() and setClipBounds() to avoid object allocation overhead
src/Core/src/Platform/Android/ContextExtensions.cs	Adds ToPixels() extension method for View to avoid accessing Context property
src/Compatibility/Core/src/Android/FastRenderers/ImageElementManager.cs	Updates compatibility layer to use new optimized scale type checking method
eng/BannedSymbols.txt	Bans GetScaleType() method to prevent future performance regressions
src/Core/tests/DeviceTests/Core.DeviceTests.csproj	Adds IsTestProject property for proper test project identification
src/Controls/tests/DeviceTests/Controls.DeviceTests.csproj	Adds IsTestProject property for proper test project identification

[Copilot]

The new ToPixels extension method for View lacks XML documentation. Consider adding documentation explaining its purpose and how it differs from the Context.ToPixels method.

Suggested change

	/// <summary>
	/// Converts a <see cref="Graphics.Rect"/> from device-independent pixels (DP) to physical pixels using the display metrics associated with the specified <see cref="View"/>.
	/// This differs from <see cref="Context.ToPixels(Graphics.Rect)"/> in that it uses the metrics of the <see cref="View"/>, which may be different from those of the <see cref="Context"/>.
	/// </summary>
	/// <param name="view">The <see cref="View"/> whose display metrics are used for conversion.</param>
	/// <param name="rectangle">The rectangle in device-independent pixels (DP) to convert.</param>
	/// <returns>
	/// A tuple containing the left, top, right, and bottom coordinates of the rectangle in physical pixels.
	/// </returns>

[jonathanpeppers]

It's internal, so I didn't document it yet. Its purpose is to avoid calling View.Context in the first place.