ContentViewGroup.cs

using System;
using Android.Content;
using Android.Graphics;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Microsoft.Maui.Graphics;
using Microsoft.Maui.Graphics.Platform;

namespace Microsoft.Maui.Platform
{
	public class ContentViewGroup : PlatformContentViewGroup, ICrossPlatformLayoutBacking, IVisualTreeElementProvidable
	{
		IBorderStroke? _clip;
		readonly Context _context;

		public ContentViewGroup(Context context) : base(context)
		{
			_context = context;
		}

		public ContentViewGroup(IntPtr javaReference, JniHandleOwnership transfer) : base(javaReference, transfer)
		{
			var context = Context;
			ArgumentNullException.ThrowIfNull(context);
			_context = context;
		}

		public ContentViewGroup(Context context, IAttributeSet attrs) : base(context, attrs)
		{
			_context = context;
		}

		public ContentViewGroup(Context context, IAttributeSet attrs, int defStyleAttr) : base(context, attrs, defStyleAttr)
		{
			_context = context;
		}

		public ContentViewGroup(Context context, IAttributeSet attrs, int defStyleAttr, int defStyleRes) : base(context, attrs, defStyleAttr, defStyleRes)
		{
			_context = context;
		}

		public ICrossPlatformLayout? CrossPlatformLayout
		{
			get; set;
		}

		Graphics.Size CrossPlatformMeasure(double widthConstraint, double heightConstraint)
		{
			return CrossPlatformLayout?.CrossPlatformMeasure(widthConstraint, heightConstraint) ?? Graphics.Size.Zero;
		}

		Graphics.Size CrossPlatformArrange(Graphics.Rect bounds)
		{
			return CrossPlatformLayout?.CrossPlatformArrange(bounds) ?? Graphics.Size.Zero;
		}

		protected override void OnMeasure(int widthMeasureSpec, int heightMeasureSpec)
		{
			{
				if (CrossPlatformLayout is IViewHandler handler &&
					handler.VirtualView is IScrollView scrollView && 
					scrollView.Orientation == ScrollOrientation.Horizontal)
				{
					System.Diagnostics.Debug.WriteLine($"");
					System.Diagnostics.Debug.WriteLine($"OnMeasure Start {scrollView} {widthMeasureSpec} {heightMeasureSpec}");
				}
			}

			if (CrossPlatformMeasure == null)
			{
				base.OnMeasure(widthMeasureSpec, heightMeasureSpec);
				return;
			}

			var deviceIndependentWidth = widthMeasureSpec.ToDouble(_context);
			var deviceIndependentHeight = heightMeasureSpec.ToDouble(_context);

			var widthMode = MeasureSpec.GetMode(widthMeasureSpec);
			var heightMode = MeasureSpec.GetMode(heightMeasureSpec);

			var measure = CrossPlatformMeasure(deviceIndependentWidth, deviceIndependentHeight);

			// If the measure spec was exact, we should return the explicit size value, even if the content
			// measure came out to a different size
			var width = widthMode == MeasureSpecMode.Exactly ? deviceIndependentWidth : measure.Width;
			var height = heightMode == MeasureSpecMode.Exactly ? deviceIndependentHeight : measure.Height;

			var platformWidth = _context.ToPixels(width);
			var platformHeight = _context.ToPixels(height);

			// Minimum values win over everything
			platformWidth = Math.Max(MinimumWidth, platformWidth);
			platformHeight = Math.Max(MinimumHeight, platformHeight);

			SetMeasuredDimension((int)platformWidth, (int)platformHeight);

			{
				if (CrossPlatformLayout is IViewHandler handler &&
					handler.VirtualView is IScrollView scrollView && 
					scrollView.Orientation == ScrollOrientation.Horizontal)
				{
					System.Diagnostics.Debug.WriteLine($"OnMeasure End {scrollView} {platformWidth} {platformHeight}");
				}
			}
		}

		protected override void OnLayout(bool changed, int left, int top, int right, int bottom)
		{
			if (CrossPlatformArrange == null)
			{
				return;
			}

			var destination = _context.ToCrossPlatformRectInReferenceFrame(left, top, right, bottom);

			CrossPlatformArrange(destination);

			if (CrossPlatformLayout is IViewHandler handler &&
				handler.VirtualView is IScrollView scrollView && 
				scrollView.Orientation == ScrollOrientation.Horizontal)
			{
				System.Diagnostics.Debug.WriteLine($"OnLayout {scrollView} {destination} {left} {top} {right} {bottom}");
				System.Diagnostics.Debug.WriteLine($"");
			}
		}

		internal IBorderStroke? Clip
		{
			get => _clip;
			set
			{
				_clip = value;
				// NOTE: calls PostInvalidate()
				SetHasClip(_clip is not null);
			}
		}

		protected override Path? GetClipPath(int width, int height)
		{
			if (Clip is null || Clip?.Shape is null)
				return null;

			float density = _context.GetDisplayDensity();
			float strokeThickness = (float)Clip.StrokeThickness;
			float w = (width / density) - strokeThickness;
			float h = (height / density) - strokeThickness;
			float x = strokeThickness / 2;
			float y = strokeThickness / 2;
			IShape clipShape = Clip.Shape;

			var bounds = new Graphics.RectF(x, y, w, h);

			Path? platformPath = clipShape.ToPlatform(bounds, strokeThickness, density, true);
			return platformPath;
		}

		IVisualTreeElement? IVisualTreeElementProvidable.GetElement()
		{
			if (CrossPlatformLayout is IVisualTreeElement layoutElement &&
				layoutElement.IsThisMyPlatformView(this))
			{
				return layoutElement;
			}

			return null;
		}
	}
}