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

[praveenkumarkarunanithi]

Root Cause

MAUI intentionally sets SetClipChildren(false) on layout containers to allow child views to render outside their bounds for visual effects such as shadows. However, on Android, a hardware-accelerated WebView renders immediately when it is added to the view hierarchy—before the layout system computes its final bounds. When combined with disabled clipping, the WebView briefly renders at full-screen size before being constrained to its actual layout bounds, causing a visible flash that is more noticeable on slower devices.

Description of Change

To prevent the initial full-screen flash, ClipBounds is applied to constrain WebView rendering to its allocated bounds. The WebView is initialized with an empty clip (0×0) to block rendering before layout completes. Once layout is finalized, the clip is updated to the actual bounds, allowing rendering only at the correct size.
Because WebView rendering is hardware-accelerated and occurs asynchronously before layout callbacks are invoked. Using ClipBounds ensures the WebView never renders outside its intended bounds, eliminating the visual flash.

Issues Fixed

Fixes #31475

Tested the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Note:
Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render.

Output Video

HybridWebView - Before Issue Fix	After Issue Fix
withoutfix_hybridwebview.mov	withfix_hybridwebview.mov

WebView - Before Issue Fix	After Issue Fix
withoutfix_webview.mov	withfix_webview.mov

[Copilot]

Pull request overview

This PR fixes a visual bug on Android where WebView and HybridWebView briefly flash at full screen size before their layout bounds are properly calculated. The root cause is that MAUI disables clipping on layout containers (to support effects like shadows), and Android's hardware-accelerated WebViews render immediately upon being added to the view hierarchy—before layout completes. The fix applies ClipBounds to constrain the WebView rendering, initializing it with an empty clip (0×0) and updating it to the actual size once OnSizeChanged is called with positive dimensions.

Key Changes

• Adds ClipBounds management to both MauiWebView and MauiHybridWebView to prevent initial full-screen flash
• Introduces OnSizeChanged override to update clip bounds after layout completes
• Updates PublicAPI.Unshipped.txt with new public OnSizeChanged method signatures

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Core/src/PublicAPI/net-android/PublicAPI.Unshipped.txt	Adds public API entries for OnSizeChanged overrides in MauiWebView and MauiHybridWebView
src/Core/src/Platform/Android/MauiWebView.cs	Implements ClipBounds initialization and OnSizeChanged override to constrain WebView rendering during layout
src/Core/src/Platform/Android/MauiHybridWebView.cs	Implements identical ClipBounds logic as MauiWebView for HybridWebView consistency

[rmarinho]

🤖 AI Summary

📊 Expand Full Review

---

🔍 Pre-Flight — Context & Validation

---

📝 Review Session — update · f3dd31c

---

Issue: #31475 - [Android] HybridWebView briefly resizes to full screen when page is opened before snapping back to correct size
Platforms Affected: Android only
Files Changed: 2 implementation files, 1 public API file

Issue Summary

On Android, WebView and HybridWebView briefly render at full-screen size before snapping to their correct bounds. This happens because MAUI intentionally sets SetClipChildren(false) on layout containers to allow shadows/visual effects, and hardware-accelerated WebViews render asynchronously before layout bounds are computed.

The issue is confirmed as Android-only, verified reproducible, and milestoned for .NET 10 Servicing.

Fix Approach (PR's Fix)

• Constructor: Initialize ClipBounds to an empty Rect(0,0,0,0) to block rendering before layout completes
• OnSizeChanged override: Once dimensions become positive, update ClipBounds to actual bounds
• Applied identically to both MauiWebView and MauiHybridWebView

Files Changed

File	Type	Changes
src/Core/src/Platform/Android/MauiHybridWebView.cs	Fix	+20 lines
src/Core/src/Platform/Android/MauiWebView.cs	Fix	+20 lines
src/Core/src/PublicAPI/net-android/PublicAPI.Unshipped.txt	API tracking	+2 entries

PR Discussion / Review Comments

Two unresolved review comments from copilot-pull-request-reviewer:

File:Line	Reviewer Says	Status
MauiWebView.cs:35	OnSizeChanged doesn't reset ClipBounds to empty when size becomes 0 (hidden/collapsed view) — stale non-zero clip bounds could allow unwanted rendering	⚠️ UNRESOLVED
MauiHybridWebView.cs:42	Same issue — no else branch to reset to empty rect when width/height becomes 0	⚠️ UNRESOLVED

No Automated Tests

The PR author explicitly states: "Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render."

No existing test files found for issue #31475 in the test projects.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33207	Set empty ClipBounds in ctor, update in OnSizeChanged	⏳ PENDING (Gate)	MauiHybridWebView.cs, MauiWebView.cs	Original PR

---

🚦 Gate — Test Verification

---

📝 Review Session — update · f3dd31c

---

Result: ❌ FAILED — No automated tests exist
Platform: android
Mode: Test existence check

Finding

No test files exist for issue #31475 in any test project:

• src/Controls/tests/TestCases.HostApp/Issues/ — no Issue31475 file
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/ — no Issue31475 file

Why Tests Cannot Be Automated

The PR author explicitly documented this limitation:

"Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render."

This is a visual timing bug — the WebView flashes full-screen for a few frames before layout is computed. There is no observable state (label text, element size, callback) that an automated UI test can capture to distinguish the broken vs fixed behavior.

Decision

Gate FAILED due to no automatable tests. Proceeding to Report phase for code-review-based recommendation per autonomous execution rules (visual timing bugs cannot be automated — this is a legitimate blocker, not a test quality issue).

---

🔧 Fix — Analysis & Comparison

---

📝 Review Session — update · f3dd31c

---

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33207	Set empty ClipBounds in ctor, update in OnSizeChanged	✅ PASS (Gate blocked — no automatable tests; code review validates correctness)	MauiHybridWebView.cs, MauiWebView.cs	Original PR

Exhausted: N/A — try-fix skipped (no automated tests exist for visual timing bug; cannot run test-based validation)

Selected Fix: PR's fix — ClipBounds approach is technically sound and correctly addresses the root cause.

Why try-fix was skipped

The Gate phase confirmed no automated tests exist for this visual timing issue. The PR author documented that automated tests cannot capture frame-level rendering artifacts. Since try-fix relies on running BuildAndRunHostApp.ps1 -TestFilter "Issue31475" to validate candidates, it cannot operate without a test to pass/fail. Proceeding to Report with code review analysis.

---

📋 Report — Final Recommendation

---

📝 Review Session — update · f3dd31c

---

⚠️ Final Recommendation: REQUEST CHANGES

Summary

PR #33207 fixes a legitimate Android-only visual bug where WebView and HybridWebView briefly render at full-screen before being constrained to their layout bounds. The fix approach is technically sound, but two unresolved code review concerns should be addressed before merge.

Root Cause

MAUI sets SetClipChildren(false) on layout containers to allow shadows/visual effects. On Android, hardware-accelerated WebViews render asynchronously via the GPU before the layout system has computed final bounds. With clipping disabled, this causes a brief full-screen render artifact on the first frame, most visible on slower devices.

Fix Quality

What works well:

• Setting ClipBounds = Rect(0,0,0,0) in the constructor correctly blocks all rendering until layout completes
• Overriding OnSizeChanged to update ClipBounds when dimensions become positive is the right hook
• The fix is applied consistently to both MauiWebView and MauiHybridWebView
• PublicAPI.Unshipped.txt correctly tracks the new protected override method
• The _clipRect reuse pattern (mutate via .Set(), then reassign ClipBounds) is correct — Android's View.ClipBounds setter copies the Rect

Issues requiring changes:

1. Missing else branch in OnSizeChanged (both files)
   The OnSizeChanged override only updates ClipBounds when width > 0 && height > 0, but does not reset it to empty when the dimensions become zero (e.g., WebView collapsed in a 0-height row, or dynamically hidden). Once a WebView has been shown and then collapsed, stale non-zero clip bounds remain — potentially allowing GPU rendering outside the intended empty region.

   The fix from the code reviewer is correct and should be applied to both files:

   if (width > 0 && height > 0)
   {
       _clipRect.Set(0, 0, width, height);
       ClipBounds = _clipRect;
   }
   else
   {
       // When the WebView becomes zero-sized or hidden, reset clip bounds to empty
       // to maintain consistency with the initial state and prevent unwanted rendering.
       _clipRect.Set(0, 0, 0, 0);
       ClipBounds = _clipRect;
   }

Platform Coverage

The fix is correctly scoped to Android-only files (Platform/Android/). No iOS, Windows, or MacCatalyst changes are needed — the issue does not reproduce on those platforms.

Gate Status

Gate FAILED — no automatable tests exist. This is a visual timing bug (frame-level rendering artifact) that cannot be captured by automated UI tests. The PR author documented this limitation explicitly. The code review recommendation is based on code analysis only.

Minor Observations (Non-blocking)

• MauiHybridWebView uses private readonly for the handler field but no access modifier on _clipRect. Inconsistent style, but not a bug.
• An alternative would be to use ClipBounds = null to clear clipping entirely, but Rect(0,0,0,0) is more explicit and correct for the initial "hidden" state.

---

📋 Expand PR Finalization Review

---

Title: ⚠️ Needs Update

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

Issues:

• Grammatically awkward — "Fix for WebView/HybridWebView briefly flashes…" reads as "Fix for [WebView briefly flashes]"
• Uses "Fix for" prefix style which is verbose
• Should describe what the code does, not just "Fix for issue"

Recommended: [Android] WebView/HybridWebView: Fix full-screen flash before layout completes via ClipBounds

Description: ✅ Good

• Grammatically awkward — "Fix for WebView/HybridWebView briefly flashes…" reads as "Fix for [WebView briefly flashes]"
• Uses "Fix for" prefix style which is verbose
• Should describe what the code does, not just "Fix for issue"

✨ Suggested PR Description

[!NOTE]
Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Root Cause

MAUI intentionally sets SetClipChildren(false) on layout containers to allow child views to render outside their bounds for visual effects such as shadows. However, on Android, a hardware-accelerated WebView renders immediately when it is added to the view hierarchy—before the layout system computes its final bounds. When combined with disabled clipping, the WebView briefly renders at full-screen size before being constrained to its actual layout bounds, causing a visible flash that is most noticeable on slower devices or when the page contains complex XAML.

Description of Change

To prevent the initial full-screen flash, ClipBounds is applied to constrain WebView rendering to its allocated bounds during layout:

• MauiWebView and MauiHybridWebView are both initialized with an empty ClipBounds (Rect(0, 0, 0, 0)) in their constructors, blocking rendering before layout completes.
• An OnSizeChanged override then updates ClipBounds to the actual view dimensions once layout finalizes, enabling correct rendering at the right size.

Because WebView rendering is hardware-accelerated and occurs asynchronously before layout callbacks are invoked, using ClipBounds ensures the WebView never renders outside its intended bounds, eliminating the visual flash.

Issues Fixed

Fixes #31475

Platforms Affected

• Android — primary fix; affects both WebView and HybridWebView
• iOS / Windows / Mac — not affected (issue is Android-only), verified no regression

Note:
Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render.

Code Review: ⚠️ Issues Found

Code Review — PR #33207

🔴 Critical Issues

None.

---

🟡 Suggestions

1. OnSizeChanged does not reset ClipBounds when size becomes zero (open review comment)

Files:

• src/Core/src/Platform/Android/MauiWebView.cs (line ~35)
• src/Core/src/Platform/Android/MauiHybridWebView.cs (line ~42)

Problem:
The OnSizeChanged override only updates ClipBounds when width > 0 && height > 0. If the WebView is later hidden (size shrinks to 0), ClipBounds retains the last non-zero value. This is inconsistent with the initial empty-rect state and could allow unintended rendering when the WebView is invisible.

This is flagged by 2 open, unresolved review comments from copilot-pull-request-reviewer (posted 2025-12-19). They should be addressed before merge.

Recommendation: Add an else branch to both OnSizeChanged overrides:

protected override void OnSizeChanged(int width, int height, int oldWidth, int oldHeight)
{
    base.OnSizeChanged(width, height, oldWidth, oldHeight);

    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;
    }
}

The same change applies identically to both MauiWebView.cs and MauiHybridWebView.cs.

---

2. PublicAPI.Unshipped.txt — OnSizeChanged becomes a public API override

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

Observation:
Overriding OnSizeChanged promotes it to a trackable public API entry:

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

This is correct and expected — both classes are public, so overriding a protected method increases the API surface. The entries are correctly added to PublicAPI.Unshipped.txt. No action required, but reviewers should be aware this is a minor API surface addition.

---

✅ Looks Good

• Fix is consistent: Both MauiWebView and MauiHybridWebView receive identical treatment, which is correct since the issue affects both.
• Root cause correctly diagnosed: The interaction between SetClipChildren(false) (parent containers) and hardware-accelerated WebView rendering is the actual cause, and ClipBounds is a targeted, low-impact solution.
• Constructor pattern is correct: Setting ClipBounds to an empty Rect(0,0,0,0) in the constructor before any layout occurs is the right place to block the initial render.
• _clipRect mutation pattern is correct: Android.Graphics.Rect is a mutable class; calling _clipRect.Set(...) and re-assigning ClipBounds = _clipRect is valid. Android's View.ClipBounds setter copies the passed Rect, so sharing and mutating _clipRect does not cause aliasing issues.
• PR scope is appropriate: Android-only files modified; no cross-platform code touched.

---

[praveenkumarkarunanithi]

🤖 AI Summary

📊 Expand Full Review
🔍 Pre-Flight — Context & Validation
📝 Review Session — update · f3dd31c
Issue: #31475 - [Android] HybridWebView briefly resizes to full screen when page is opened before snapping back to correct size Platforms Affected: Android only Files Changed: 2 implementation files, 1 public API file

Issue Summary

On Android, WebView and HybridWebView briefly render at full-screen size before snapping to their correct bounds. This happens because MAUI intentionally sets SetClipChildren(false) on layout containers to allow shadows/visual effects, and hardware-accelerated WebViews render asynchronously before layout bounds are computed.

The issue is confirmed as Android-only, verified reproducible, and milestoned for .NET 10 Servicing.

Fix Approach (PR's Fix)

• Constructor: Initialize ClipBounds to an empty Rect(0,0,0,0) to block rendering before layout completes
• OnSizeChanged override: Once dimensions become positive, update ClipBounds to actual bounds
• Applied identically to both MauiWebView and MauiHybridWebView

Files Changed

File Type Changes
src/Core/src/Platform/Android/MauiHybridWebView.cs Fix +20 lines
src/Core/src/Platform/Android/MauiWebView.cs Fix +20 lines
src/Core/src/PublicAPI/net-android/PublicAPI.Unshipped.txt API tracking +2 entries

PR Discussion / Review Comments

Two unresolved review comments from copilot-pull-request-reviewer:

File:Line Reviewer Says Status
MauiWebView.cs:35 OnSizeChanged doesn't reset ClipBounds to empty when size becomes 0 (hidden/collapsed view) — stale non-zero clip bounds could allow unwanted rendering ⚠️ UNRESOLVED
MauiHybridWebView.cs:42 Same issue — no else branch to reset to empty rect when width/height becomes 0 ⚠️ UNRESOLVED

No Automated Tests

The PR author explicitly states: "Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render."

No existing test files found for issue #31475 in the test projects.

Fix Candidates

Source Approach Test Result Files Changed Notes

PR PR #33207 Set empty ClipBounds in ctor, update in OnSizeChanged ⏳ PENDING (Gate) MauiHybridWebView.cs, MauiWebView.cs Original PR
🚦 Gate — Test Verification
📝 Review Session — update · f3dd31c
Result: ❌ FAILED — No automated tests exist Platform: android Mode: Test existence check

Finding

No test files exist for issue #31475 in any test project:

• src/Controls/tests/TestCases.HostApp/Issues/ — no Issue31475 file
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/ — no Issue31475 file

Why Tests Cannot Be Automated

The PR author explicitly documented this limitation:

"Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render."

This is a visual timing bug — the WebView flashes full-screen for a few frames before layout is computed. There is no observable state (label text, element size, callback) that an automated UI test can capture to distinguish the broken vs fixed behavior.

Decision

Gate FAILED due to no automatable tests. Proceeding to Report phase for code-review-based recommendation per autonomous execution rules (visual timing bugs cannot be automated — this is a legitimate blocker, not a test quality issue).

🔧 Fix — Analysis & Comparison
📝 Review Session — update · f3dd31c

Fix Candidates

Source Approach Test Result Files Changed Notes

PR PR #33207 Set empty ClipBounds in ctor, update in OnSizeChanged ✅ PASS (Gate blocked — no automatable tests; code review validates correctness) MauiHybridWebView.cs, MauiWebView.cs Original PR
Exhausted: N/A — try-fix skipped (no automated tests exist for visual timing bug; cannot run test-based validation)

Selected Fix: PR's fix — ClipBounds approach is technically sound and correctly addresses the root cause.

Why try-fix was skipped

The Gate phase confirmed no automated tests exist for this visual timing issue. The PR author documented that automated tests cannot capture frame-level rendering artifacts. Since try-fix relies on running BuildAndRunHostApp.ps1 -TestFilter "Issue31475" to validate candidates, it cannot operate without a test to pass/fail. Proceeding to Report with code review analysis.

📋 Report — Final Recommendation
📝 Review Session — update · f3dd31c

⚠️ Final Recommendation: REQUEST CHANGES

Summary

PR #33207 fixes a legitimate Android-only visual bug where WebView and HybridWebView briefly render at full-screen before being constrained to their layout bounds. The fix approach is technically sound, but two unresolved code review concerns should be addressed before merge.

Root Cause

MAUI sets SetClipChildren(false) on layout containers to allow shadows/visual effects. On Android, hardware-accelerated WebViews render asynchronously via the GPU before the layout system has computed final bounds. With clipping disabled, this causes a brief full-screen render artifact on the first frame, most visible on slower devices.

Fix Quality

What works well:

• Setting ClipBounds = Rect(0,0,0,0) in the constructor correctly blocks all rendering until layout completes
• Overriding OnSizeChanged to update ClipBounds when dimensions become positive is the right hook
• The fix is applied consistently to both MauiWebView and MauiHybridWebView
• PublicAPI.Unshipped.txt correctly tracks the new protected override method
• The _clipRect reuse pattern (mutate via .Set(), then reassign ClipBounds) is correct — Android's View.ClipBounds setter copies the Rect

Issues requiring changes:

1. Missing else branch in OnSizeChanged (both files)
   The OnSizeChanged override only updates ClipBounds when width > 0 && height > 0, but does not reset it to empty when the dimensions become zero (e.g., WebView collapsed in a 0-height row, or dynamically hidden). Once a WebView has been shown and then collapsed, stale non-zero clip bounds remain — potentially allowing GPU rendering outside the intended empty region.
   The fix from the code reviewer is correct and should be applied to both files:

   if (width > 0 && height > 0)
   {
       _clipRect.Set(0, 0, width, height);
       ClipBounds = _clipRect;
   }
   else
   {
       // When the WebView becomes zero-sized or hidden, reset clip bounds to empty
       // to maintain consistency with the initial state and prevent unwanted rendering.
       _clipRect.Set(0, 0, 0, 0);
       ClipBounds = _clipRect;
   }

Platform Coverage

The fix is correctly scoped to Android-only files (Platform/Android/). No iOS, Windows, or MacCatalyst changes are needed — the issue does not reproduce on those platforms.

Gate Status

Gate FAILED — no automatable tests exist. This is a visual timing bug (frame-level rendering artifact) that cannot be captured by automated UI tests. The PR author documented this limitation explicitly. The code review recommendation is based on code analysis only.

Minor Observations (Non-blocking)

• MauiHybridWebView uses private readonly for the handler field but no access modifier on _clipRect. Inconsistent style, but not a bug.
• An alternative would be to use ClipBounds = null to clear clipping entirely, but Rect(0,0,0,0) is more explicit and correct for the initial "hidden" state.

📋 Expand PR Finalization Review
Title: ⚠️ Needs Update

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

Issues:

• Grammatically awkward — "Fix for WebView/HybridWebView briefly flashes…" reads as "Fix for [WebView briefly flashes]"
• Uses "Fix for" prefix style which is verbose
• Should describe what the code does, not just "Fix for issue"

Recommended: [Android] WebView/HybridWebView: Fix full-screen flash before layout completes via ClipBounds

Description: ✅ Good

• Grammatically awkward — "Fix for WebView/HybridWebView briefly flashes…" reads as "Fix for [WebView briefly flashes]"
• Uses "Fix for" prefix style which is verbose
• Should describe what the code does, not just "Fix for issue"

✨ Suggested PR Description

[!NOTE]
Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Root Cause

MAUI intentionally sets SetClipChildren(false) on layout containers to allow child views to render outside their bounds for visual effects such as shadows. However, on Android, a hardware-accelerated WebView renders immediately when it is added to the view hierarchy—before the layout system computes its final bounds. When combined with disabled clipping, the WebView briefly renders at full-screen size before being constrained to its actual layout bounds, causing a visible flash that is most noticeable on slower devices or when the page contains complex XAML.

Description of Change

To prevent the initial full-screen flash, ClipBounds is applied to constrain WebView rendering to its allocated bounds during layout:

• MauiWebView and MauiHybridWebView are both initialized with an empty ClipBounds (Rect(0, 0, 0, 0)) in their constructors, blocking rendering before layout completes.
• An OnSizeChanged override then updates ClipBounds to the actual view dimensions once layout finalizes, enabling correct rendering at the right size.

Because WebView rendering is hardware-accelerated and occurs asynchronously before layout callbacks are invoked, using ClipBounds ensures the WebView never renders outside its intended bounds, eliminating the visual flash.

Issues Fixed

Fixes #31475

Platforms Affected

• Android — primary fix; affects both WebView and HybridWebView
• iOS / Windows / Mac — not affected (issue is Android-only), verified no regression

Note: Visual timing bugs occurring between render frames cannot be detected by automated tests, as the flash happens before layout completes and no measurable state captures the momentary incorrect render.

Code Review: ⚠️ Issues Found

Code Review — PR #33207

🔴 Critical Issues

None.

🟡 Suggestions

1. OnSizeChanged does not reset ClipBounds when size becomes zero (open review comment)

Files:

• src/Core/src/Platform/Android/MauiWebView.cs (line ~35)
• src/Core/src/Platform/Android/MauiHybridWebView.cs (line ~42)

Problem: The OnSizeChanged override only updates ClipBounds when width > 0 && height > 0. If the WebView is later hidden (size shrinks to 0), ClipBounds retains the last non-zero value. This is inconsistent with the initial empty-rect state and could allow unintended rendering when the WebView is invisible.

This is flagged by 2 open, unresolved review comments from copilot-pull-request-reviewer (posted 2025-12-19). They should be addressed before merge.

Recommendation: Add an else branch to both OnSizeChanged overrides:

protected override void OnSizeChanged(int width, int height, int oldWidth, int oldHeight)
{
    base.OnSizeChanged(width, height, oldWidth, oldHeight);

    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;
    }
}

The same change applies identically to both MauiWebView.cs and MauiHybridWebView.cs.

2. PublicAPI.Unshipped.txt — OnSizeChanged becomes a public API override

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

Observation: Overriding OnSizeChanged promotes it to a trackable public API entry:

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

This is correct and expected — both classes are public, so overriding a protected method increases the API surface. The entries are correctly added to PublicAPI.Unshipped.txt. No action required, but reviewers should be aware this is a minor API surface addition.

✅ Looks Good

• Fix is consistent: Both MauiWebView and MauiHybridWebView receive identical treatment, which is correct since the issue affects both.
• Root cause correctly diagnosed: The interaction between SetClipChildren(false) (parent containers) and hardware-accelerated WebView rendering is the actual cause, and ClipBounds is a targeted, low-impact solution.
• Constructor pattern is correct: Setting ClipBounds to an empty Rect(0,0,0,0) in the constructor before any layout occurs is the right place to block the initial render.
• _clipRect mutation pattern is correct: Android.Graphics.Rect is a mutable class; calling _clipRect.Set(...) and re-assigning ClipBounds = _clipRect is valid. Android's View.ClipBounds setter copies the passed Rect, so sharing and mutating _clipRect does not cause aliasing issues.
• PR scope is appropriate: Android-only files modified; no cross-platform code touched.

Addressed the AI Agent's concern — added the else branch to OnSizeChanged in both MauiWebView and MauiHybridWebView to reset ClipBounds to (0,0,0,0) when the view becomes zero-sized. Tested the dynamic show/hide scenario locally and confirmed the fix works as expected. No pending concerns remaining.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 33207

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 33207"

[MauiBot]

🚦 Gate - Test Before and After Fix

📊 Expand Full Gate — 699553f · Merge branch 'dotnet:main' into fix-31475

---

Gate Result: ⚠️ SKIPPED

No tests were detected in this PR.

Recommendation: Add tests to verify the fix using the write-tests-agent:

@copilot write tests for this PR

The agent will analyze the issue, determine the appropriate test type (UI test, device test, unit test, or XAML test), and create tests that verify the fix.

---

[MauiBot]

🤖 AI Summary

📊 Expand Full Review — 699553f · Merge branch 'dotnet:main' into fix-31475

---

🔍 Pre-Flight — Context & Validation

---

Issue: #31475 - [Android] HybridWebView briefly resizes to full screen when page is opened before snapping back to correct size
PR: #33207 - [Android] Fix for WebView/HybridWebView briefly flashes full screen before layout completes
Platforms Affected: Android only
Files Changed: 2 implementation files, 1 public API file

Key Findings

• MAUI intentionally sets SetClipChildren(false) on layout containers to allow visual effects (shadows), which means WebView can render outside parent bounds
• Hardware-accelerated WebView on Android renders asynchronously (before layout bounds are finalized), causing the full-screen flash
• PR uses ClipBounds = Rect(0,0,0,0) in constructor to block rendering, then updates in OnSizeChanged — consistent with existing pattern in LayoutViewGroup.cs (lines 153–161)
• Previous Copilot review feedback (handle zero-size case) was incorporated — PR includes else branch resetting to empty rect
• Gate skipped: no automated tests — PR author explains this is a visual timing bug occurring between render frames, not detectable by automation
• Issue commenters confirmed IsClippedToBounds=true on wrapper Grid and disabling hardware acceleration are viable workarounds
• PublicAPI.Unshipped.txt is missing trailing newline at end of file (minor)
• _clipRect field in MauiHybridWebView.cs uses readonly without explicit private modifier (minor style inconsistency vs other fields that use private readonly)

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33207	Apply ClipBounds = Rect(0,0,0,0) in constructor; update to actual bounds in OnSizeChanged for both MauiWebView and MauiHybridWebView	⏳ PENDING	MauiWebView.cs, MauiHybridWebView.cs, PublicAPI.Unshipped.txt	Original PR

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🔧 Fix — Analysis & Comparison

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Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	claude-opus-4.6	ClipBounds=Rect(0,0,0,0) in constructor + OnLayout override	⚠️ Blocked	MauiWebView.cs, MauiHybridWebView.cs	Builds OK; OnLayout is deprecated in Android API 36 (CS0618 warning); semantically cleaner but deprecated
2	claude-sonnet-4.6	Handler-level fix: ClipBounds=Rect(0,0,0,0) in CreatePlatformView + one-shot IOnGlobalLayoutListener in ConnectHandler sets ClipBounds=null after first layout	⚠️ Blocked	WebViewHandler.Android.cs, HybridWebViewHandler.Android.cs, PublicAPI.Unshipped.txt	Compiles cleanly (0 errors, 0 warnings); avoids override in platform view subclasses; slightly more complex
3	gpt-5.3-codex	LayoutViewGroup parent-level SetClipChildren(true) toggle via OnViewAdded/OnViewRemoved when WebView child detected	❌ Fail	LayoutViewGroup.cs	Build command syntax error (MSBuild /bl:false invalid); code approach interesting but untested
4	gpt-5.4	SetLayerType(Software) in constructor + IOnPreDrawListener to restore LayerType.None after first pre-draw with valid bounds	❌ Fail	MauiWebView.cs, MauiHybridWebView.cs	Build env error (MSB3644, wrong TFM); code approach valid but has potential WebView performance concerns
PR	PR #33207	ClipBounds=Rect(0,0,0,0) in constructor + OnSizeChanged override updates to actual bounds; else branch resets to empty on zero-size	⏳ No tests	MauiWebView.cs, MauiHybridWebView.cs, PublicAPI.Unshipped.txt	Visual timing bug — no automated test possible; consistent with LayoutViewGroup.cs existing pattern

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	No	"NO NEW IDEAS" — solution space exhausted; confirmed PR's fix is most sound

Exhausted: Yes
Selected Fix: PR's fix — ClipBounds approach in constructor + OnSizeChanged is the most pragmatic: non-deprecated API, operates at the right level (the view itself), consistent with existing LayoutViewGroup pattern, no layer-type side effects, no external listener registration complexity. Attempt 2 (handler-level) is a clean alternative but adds more indirection without benefit.

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📋 Report — Final Recommendation

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✅ Final Recommendation: APPROVE

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #31475, Android-only, 2 impl files + PublicAPI
Gate	⚠️ SKIPPED	No automated tests detected — visual timing bug between render frames
Try-Fix	✅ COMPLETE	4 attempts (2 Blocked, 2 Fail due to env); PR's fix confirmed best
Report	✅ COMPLETE	Selected Fix: PR

Summary

PR #33207 fixes a well-defined Android rendering bug where MauiWebView and MauiHybridWebView briefly flash at full-screen size before layout completes. The fix is minimal, targeted, and consistent with the existing LayoutViewGroup.cs clip-bounds pattern. Four alternative approaches were explored; none is superior to the PR's fix. The PR author and prior Copilot reviewer have already iterated on the code (zero-size else-branch incorporated). Two minor nits remain.

Root Cause

MAUI sets SetClipChildren(false) on layout containers to support shadow/visual effects. Android's hardware-accelerated WebView renders asynchronously via the GPU before the layout system has finalized view bounds. With clipping disabled, the WebView's initial full-size GPU frame is visible for a brief moment, producing the flash.

Fix Quality

Sound. The approach applies ClipBounds = Rect(0,0,0,0) in the constructor to completely block GPU rendering until layout is complete, then updates to actual bounds in OnSizeChanged. This is:

• ✅ Consistent with LayoutViewGroup.cs existing pattern (lines 153–161)
• ✅ Uses non-deprecated API (OnSizeChanged vs OnLayout which is deprecated in API 36)
• ✅ Handles zero-size/hidden case in the else branch
• ✅ No performance concerns (ClipBounds is a lightweight GPU scissor test)
• ✅ No observer registration complexity or layer-type side effects

Minor nits (non-blocking):

1. PublicAPI.Unshipped.txt is missing a trailing newline at end of file (the diff shows \ No newline at end of file)
2. _clipRect field in MauiHybridWebView.cs lacks an explicit private modifier, inconsistent with _handler and _androidAppOriginUri in the same class which use private — while functionally equivalent, explicit access modifiers improve readability

Tests: No automated tests exist for this visual timing fix, which is expected — the flash occurs between render frames before any measurable state is set. The PR author documented this clearly. The gate correctly skipped rather than blocking the PR.

Try-Fix conclusion: The PR's fix was selected as the best approach. The handler-level alternative (Attempt 2) would also work but adds indirection without benefit. The PR's OnSizeChanged approach is the simplest and most idiomatic solution.

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[kubaflo]

Could you please review the AI's summary?

[praveenkumarkarunanithi]

Could you please review the AI's summary?

Could you please review the AI's summary?

@kubaflo Reviewed the AI summary. The suggested alternative (Visibility + OnPreDrawListener) introduces unnecessary complexity and potential side effects. The ClipBounds approach is simpler, directly constrains GPU rendering, and aligns with the existing pattern in LayoutViewGroup.cs (lines 153–162). The Gate failure is due to the absence of automated tests, which is already documented — this visual timing issue occurs between render frames and cannot be reliably captured by automation. All prior review concerns are addressed.