[Android] Fix for WebView/HybridWebView briefly flashes full screen before layout completes

src/Core/src/Platform/Android/MauiHybridWebView.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using Android.Content;
+using Android.Graphics;
 using Android.Webkit;
 using AUri = Android.Net.Uri;
 using AWebView = Android.Webkit.WebView;
@@ -15,11 +16,37 @@ public class MauiHybridWebView : AWebView, IHybridPlatformWebView
 	{
 		private readonly WeakReference<HybridWebViewHandler> _handler;
 		private static readonly AUri AndroidAppOriginUri = AUri.Parse(HybridWebViewHandler.AppOrigin)!;
+		readonly Rect _clipRect;
 
 		public MauiHybridWebView(HybridWebViewHandler handler, Context context) : base(context)
 		{
 			ArgumentNullException.ThrowIfNull(handler, nameof(handler));
 			_handler = new WeakReference<HybridWebViewHandler>(handler);
+
+			// Initialize with empty clip bounds to prevent the WebView from briefly
+			// rendering at full screen size before layout is complete.
+			// https://github.com/dotnet/maui/issues/31475
+			_clipRect = new Rect(0, 0, 0, 0);
+			ClipBounds = _clipRect;
+		}
+
+		protected override void OnSizeChanged(int width, int height, int oldWidth, int oldHeight)
+		{
+			base.OnSizeChanged(width, height, oldWidth, oldHeight);
+
+			// Update clip bounds to match the actual size once layout is complete.
+			if (width > 0 && height > 0)
+			{
+				_clipRect.Set(0, 0, width, height);
+				ClipBounds = _clipRect;
+			}
+			else
+			{
+				// Reset to empty rect when the view becomes zero-sized or hidden,
+				// to avoid stale non-zero clip bounds.
+				_clipRect.Set(0, 0, 0, 0);
+				ClipBounds = _clipRect;
+			}
 		}
 
 		public void SendRawMessage(string rawMessage)

src/Core/src/Platform/Android/MauiWebView.cs

@@ -1,5 +1,6 @@
 using System;
 using Android.Content;
+using Android.Graphics;
 using Android.Webkit;
 
 namespace Microsoft.Maui.Platform
@@ -9,10 +10,36 @@ public class MauiWebView : WebView, IWebViewDelegate
 		public const string AssetBaseUrl = "file:///android_asset/";
 
 		readonly WebViewHandler _handler;
+		readonly Rect _clipRect;
 
 		public MauiWebView(WebViewHandler handler, Context context) : base(context)
 		{
 			_handler = handler ?? throw new ArgumentNullException(nameof(handler));
+
+			// Initialize with empty clip bounds to prevent the WebView from briefly
+			// rendering at full screen size before layout is complete.
+			// https://github.com/dotnet/maui/issues/31475
+			_clipRect = new Rect(0, 0, 0, 0);
+			ClipBounds = _clipRect;
+		}
+
+		protected override void OnSizeChanged(int width, int height, int oldWidth, int oldHeight)
+		{
+			base.OnSizeChanged(width, height, oldWidth, oldHeight);
+
+			// Update clip bounds to match the actual size once layout is complete.
+			if (width > 0 && height > 0)
+			{
+				_clipRect.Set(0, 0, width, height);
+				ClipBounds = _clipRect;
+			}
+			else
+			{
+				// Reset to empty rect when the view becomes zero-sized or hidden,
+				// to avoid stale non-zero clip bounds.
+				_clipRect.Set(0, 0, 0, 0);
+				ClipBounds = _clipRect;
+			}
 		}
 
 		void IWebViewDelegate.LoadHtml(string? html, string? baseUrl)

src/Core/src/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -9,3 +9,5 @@ override Microsoft.Maui.PlatformDrawable.ThresholdType.get -> System.Type!
 *REMOVED*override Microsoft.Maui.Graphics.MauiDrawable.OnBoundsChange(Android.Graphics.Rect! bounds) -> void
 *REMOVED*override Microsoft.Maui.Graphics.MauiDrawable.OnDraw(Android.Graphics.Drawables.Shapes.Shape? shape, Android.Graphics.Canvas? canvas, Android.Graphics.Paint? paint) -> void
 override Microsoft.Maui.Handlers.LabelHandler.GetDesiredSize(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
+override Microsoft.Maui.Platform.MauiHybridWebView.OnSizeChanged(int width, int height, int oldWidth, int oldHeight) -> void
+override Microsoft.Maui.Platform.MauiWebView.OnSizeChanged(int width, int height, int oldWidth, int oldHeight) -> void