Fix FlexLayout Grow causes measured child sizes to be ignored by devanathan-vaithiyanathan · Pull Request #34535 · dotnet/maui

devanathan-vaithiyanathan · 2026-03-18T13:35:18Z

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!

Issue Details

Flex-grow calculation was distributing the entire container space instead of just the free space, causing items to be sized incorrectly.

Description of Change

Calculate actual free space: freeSpace = flex_dim - extra_flex_dim
Distribute only free space proportionally based on grow ratios
Preserve item's intrinsic size instead of resetting to 0

Issues Fixed

Fixes #34464

Tested the behavior in the following platforms.

Android
Windows
iOS
Mac

Before	After
Mac	Mac

github-actions · 2026-03-18T13:35:28Z

🚀 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 -- 34535

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34535"

sheiksyedm · 2026-03-19T08:54:34Z

/azp run maui-pr-uitests , maui-pr-devicetests

azure-pipelines · 2026-03-19T08:54:48Z

Azure Pipelines successfully started running 2 pipeline(s).

Copilot

Pull request overview

Fixes FlexLayout’s flex-grow sizing so that grow distribution uses only available free space and preserves measured child sizes, addressing incorrect item sizing reported in #34464.

Changes:

Update flex-grow calculation to distribute only free space (container minus measured grow-item sizes).
Preserve intrinsic/measured size for growing children rather than resetting to zero.
Add a new UI test + host repro page for issue #34464.

Reviewed changes

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

File	Description
src/Core/src/Layouts/Flex.cs	Adjusts grow sizing math to use free space and keep measured sizes.
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34464.cs	Adds UI test coverage for the reported layout issue.
src/Controls/tests/TestCases.HostApp/Issues/Issue34464.cs	Adds a host app repro page for issue #34464.

src/Core/src/Layouts/Flex.cs

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34464.cs

MauiBot · 2026-03-20T00:35:48Z

🤖 AI Summary

📊 Expand Full Review — 67592bb · snapshot added

🔍 Pre-Flight — Context & Validation

Issue: #34464 - FlexLayout Grow causes measured child sizes to be ignored
PR: #34535 - Fix FlexLayout Grow causes measured child sizes to be ignored
Platforms Affected: Android, iOS, MacCatalyst/macOS, Windows
Files Changed: 1 implementation, 3 test

Key Findings

The linked issue reports that FlexLayout.Grow=1 currently overrides each growing item's measured main-axis size instead of adding only its proportional share of remaining free space, which clips larger content and diverges from CSS flexbox behavior.
The issue author provided a concrete numeric repro and noted that commenting out the size-reset logic in src/Core/src/Layouts/Flex.cs makes MAUI behavior match CSS; the issue was later validated by triage across Android, iOS, MacCatalyst, and Windows.
The PR changes one runtime file (src/Core/src/Layouts/Flex.cs) and adds both unit coverage (src/Controls/tests/Core.UnitTests/Layouts/FlexLayoutTests.cs) and UI coverage (src/Controls/tests/TestCases.HostApp/Issues/Issue34464.cs, src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34464.cs).
Existing inline review feedback notes one potential test concern: the new UI test currently waits only for HeaderLabel, which may not guarantee that the BindableLayout-generated children have rendered before the screenshot is captured.
Edge-case context from the issue suggests the bug is most visible when items in the same flex line have very different measured widths; the reporter also suspects related behavior may overlap with issues FlexLayout.Grow="1" text cuts off instead of line break on Windows #22371 and FlexLayout misbehaves when Label content has long .Text #28165.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34535	Compute free space as `flex_dim - extra_flex_dim`, distribute only that free space to growing items, and preserve each item's measured size during PENDING (Gate)	`src/Core/src/Layouts/Flex.cs`, `src/Controls/tests/Core.UnitTests/Layouts/FlexLayoutTests.cs`, `src/Controls/tests/TestCases.HostApp/Issues/Issue34464.cs`, `src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34464.cs`	Original PR; adds both unit and UI validation.	growth.

Issue: #34464 - FlexLayout Grow causes measured child sizes to be ignored
PR: #34535 - Fix FlexLayout Grow causes measured child sizes to be ignored
Platforms Affected: Android, iOS, MacCatalyst/macOS, Windows
Files Changed: 1 implementation, 7 test/support

Key Findings

The issue reports that FlexLayout.Grow currently replaces each growing item's measured main-axis size instead of adding only its share of remaining free space, which clips larger content and diverges from CSS flexbox behavior.
The issue body includes a concrete numeric repro and points to src/Core/src/Layouts/Flex.cs as the problematic logic; triage later validated the bug across Android, iOS, MacCatalyst, and Windows.
This PR changes one runtime file, adds a focused unit test in src/Controls/tests/Core.UnitTests/Layouts/FlexLayoutTests.cs, adds a HostApp repro page plus a shared UI test for issue 34464, and includes snapshot baselines for Android, iOS, Mac, and Windows.
Prior inline review feedback flagged two important concerns: freeSpace should not go negative in the grow path, and the new UI test waits only for HeaderLabel, which may not guarantee the BindableLayout-generated children are realized before the screenshot is captured.
Prior agent review on this PR failed Gate on MacCatalyst because the new Mac screenshot baseline was missing at that time; the current PR file list now includes the requested snapshot assets, so Android gate verification is still required.
Edge-case context from the issue suggests the regression is most visible when items with very different measured widths share a flex line; the reporter also suspects overlap with issues FlexLayout.Grow="1" text cuts off instead of line break on Windows #22371 and FlexLayout misbehaves when Label content has long .Text #28165.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34535	Compute free space as `flex_dim - extra_flex_dim`, distribute only that free space to grow items, and preserve measured child sizes during growth.	⏳ PENDING (Gate)	`src/Core/src/Layouts/Flex.cs`, `src/Controls/tests/Core.UnitTests/Layouts/FlexLayoutTests.cs`, `src/Controls/tests/TestCases.HostApp/Issues/Issue34464.cs`, `src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34464.cs`, snapshot files	Original PR; adds both unit and UI coverage.

🚦 Gate — Test Verification

Gate FAILEDResult:

Platform: catalyst
Mode: Full Verification

Tests FAIL without fix:
Tests PASS with fix:

Evidence

Verification on MacCatalyst confirmed the new test detects a failure without the PR fix.
Verification with the PR fix still failed because the screenshot baseline FlexLayoutWithBindableLayoutDisplaysLabels.png was not available for the Mac test run.
This means the gate cannot validate a PASS-with-fix result on the requested platform.

Gate Result: ✅ PASSED

Result: ✅ PASSED

Platform: android
Mode: Full Verification

Tests FAIL without fix: ✅
Tests PASS with fix: ✅

Evidence

verify-tests-fail-without-fix completed full verification successfully for Issue34464 on Android.
The generated verification report records FAIL without fix and PASS with fix.
Android device logs show the HostApp launching and Appium reaching HeaderLabel, which is consistent with the successful fix-side UI verification.
The verification report also captured a transient ADB0010 install failure during the broken-baseline run before succeeding on retry; the overall gate result remained ✅ PASSED.

🔧 Fix — Analysis & Comparison

Gate FAILEDResult:

Platform: catalyst
Mode: Full Verification

Tests FAIL without fix:
Tests PASS with fix:

Evidence

Verification on MacCatalyst confirmed the new test detects a failure without the PR fix.
Verification with the PR fix still failed because the screenshot baseline FlexLayoutWithBindableLayoutDisplaysLabels.png was not available for the Mac test run.
This means the gate cannot validate a PASS-with-fix result on the requested platform.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix / claude-opus-4.6	Prevent `layout.flex_dim` inflation when grow items exist, so it already represents true free space; preserve measured size by not zeroing the frame.	✅ PASS	`src/Core/src/Layouts/Flex.cs`	Simple and correct, but changes upstream accounting behavior.
2	try-fix / claude-sonnet-4.6	Snapshot `layout.flex_dim` before inflation and use the snapshot in grow calculations while preserving measured size.	✅ PASS	`src/Core/src/Layouts/Flex.cs`	Small local-state alternative; same core math.
3	try-fix / gpt-5.3-codex	Leave inflated `layout.flex_dim` intact and subtract each child's proportional share of `layout.extra_flex_dim` directly in the grow formula.	✅ PASS	`src/Core/src/Layouts/Flex.cs`	Correct but less readable.
4	try-fix / gemini-3-pro-preview	Disable inflation for grow scenarios and preserve measured child size.	✅ PASS	`src/Core/src/Layouts/Flex.cs`	Duplicates attempt 1.
5	try-fix / claude-sonnet-4.6 (round 2)	Recompute free space from `layout.size_dim` and child frame data immediately before grow distribution.	✅ PASS	`src/Core/src/Layouts/Flex.cs`	Most independent approach, but also the heaviest and most arithmetic-sensitive.
PR	PR #34535	Compute `freeSpace = flex_dim - extra_flex_dim`, distribute only free space to grow items, and preserve measured child size.	✅ PASSED (Gate)	`src/Core/src/Layouts/Flex.cs` + tests	Best balance of locality, clarity, and correctness.

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	No	NO NEW IDEAS
claude-sonnet-4.6	2	Yes	Recompute free space from child frame data instead of bookkeeping variables; tested as attempt 5.
gpt-5.3-codex	2	No	NO NEW IDEAS
gemini-3-pro-preview	2	No	NO NEW IDEAS
claude-opus-4.6	3	No	NO NEW IDEAS
claude-sonnet-4.6	3	No	NO NEW IDEAS
gpt-5.3-codex	3	No	NO NEW IDEAS
gemini-3-pro-preview	3	No	NO NEW IDEAS

Exhausted: Yes
Selected Fix: PR's fix — it is the most localized and readable version of the correct CSS-style grow formula, and no materially better alternative emerged from five passing candidates.

📋 Report — Final Recommendation

Gate FAILEDResult:

Platform: catalyst
Mode: Full Verification

Tests FAIL without fix:
Tests PASS with fix:

Evidence

Verification on MacCatalyst confirmed the new test detects a failure without the PR fix.
Verification with the PR fix still failed because the screenshot baseline FlexLayoutWithBindableLayoutDisplaysLabels.png was not available for the Mac test run.
This means the gate cannot validate a PASS-with-fix result on the requested platform.

✅ Final Recommendation: APPROVE

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #34464 is a cross-platform FlexLayout grow-sizing bug; PR updates one runtime file and adds unit/UI coverage plus snapshots.
Gate	✅ PASSED	Android full verification proved the new test fails without fix and passes with fix.
Try-Fix	✅ COMPLETE	5 passing candidates explored; no materially better alternative than the PR fix emerged.
Report	✅ COMPLETE

Summary

PR #34535 fixes the reported FlexLayout grow regression correctly. The Android gate passed in full, and the mandatory multi-model try-fix exploration found only mathematically equivalent alternatives or heavier implementations. The PR's solution is the best tradeoff of correctness, locality, and readability.

Root Cause

The previous grow path effectively redistributed total line space instead of only the remaining free space because it zeroed each growing child's measured size and then used an inflated layout.flex_dim pool. That caused larger measured children to shrink below their natural size and clip content.

Fix Quality

The PR restores CSS-style behavior by preserving each child's measured size and distributing only true free space. Compared with the passing alternatives, this implementation is the most localized and easiest to reason about. One minor residual concern is that the UI test waits only for HeaderLabel, which may be slightly less deterministic than waiting for a templated item, but the gate passed and this does not outweigh the overall quality of the fix.

kubaflo

Could you please add snapshots?

kubaflo · 2026-03-20T12:47:07Z

/azp run maui-pr-uitests

azure-pipelines · 2026-03-20T12:47:20Z

Azure Pipelines successfully started running 1 pipeline(s).

kubaflo · 2026-03-20T18:31:46Z

/azp run maui-copilot

azure-pipelines · 2026-03-20T18:31:53Z

No pipelines are associated with this pull request.

> [!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](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you!  ### Issue Details Flex-grow calculation was distributing the entire container space instead of just the free space, causing items to be sized incorrectly. ### Description of Change  * Calculate actual free space: freeSpace = flex_dim - extra_flex_dim * Distribute only free space proportionally based on grow ratios * Preserve item's intrinsic size instead of resetting to 0 ### Issues Fixed  Fixes #34464  **Tested the behavior in the following platforms.** - [x] Android - [x] Windows - [x] iOS - [x] Mac | Before | After | |---------|--------| | **Mac** <img src="https://github.com/user-attachments/assets/2f155ddd-a04a-4217-9bd8-f294357ba171" width="600" height="300"> | **Mac** <img src="https://github.com/user-attachments/assets/cb840cc4-7c7b-4a30-aeb6-8db3a8458c79" width="600" height="300"> | --------- Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

…#34535) > [!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](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you!  ### Issue Details Flex-grow calculation was distributing the entire container space instead of just the free space, causing items to be sized incorrectly. ### Description of Change  * Calculate actual free space: freeSpace = flex_dim - extra_flex_dim * Distribute only free space proportionally based on grow ratios * Preserve item's intrinsic size instead of resetting to 0 ### Issues Fixed  Fixes dotnet#34464  **Tested the behavior in the following platforms.** - [x] Android - [x] Windows - [x] iOS - [x] Mac | Before | After | |---------|--------| | **Mac** <img src="https://github.com/user-attachments/assets/2f155ddd-a04a-4217-9bd8-f294357ba171" width="600" height="300"> | **Mac** <img src="https://github.com/user-attachments/assets/cb840cc4-7c7b-4a30-aeb6-8db3a8458c79" width="600" height="300"> | --------- Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

> [!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](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you!  ### Issue Details Flex-grow calculation was distributing the entire container space instead of just the free space, causing items to be sized incorrectly. ### Description of Change  * Calculate actual free space: freeSpace = flex_dim - extra_flex_dim * Distribute only free space proportionally based on grow ratios * Preserve item's intrinsic size instead of resetting to 0 ### Issues Fixed  Fixes #34464  **Tested the behavior in the following platforms.** - [x] Android - [x] Windows - [x] iOS - [x] Mac | Before | After | |---------|--------| | **Mac** <img src="https://github.com/user-attachments/assets/2f155ddd-a04a-4217-9bd8-f294357ba171" width="600" height="300"> | **Mac** <img src="https://github.com/user-attachments/assets/cb840cc4-7c7b-4a30-aeb6-8db3a8458c79" width="600" height="300"> | --------- Co-authored-by: Jakub Florkowski <42434498+kubaflo@users.noreply.github.com>

devanathan-vaithiyanathan added 2 commits March 16, 2026 13:45

fix added

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test added

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karthikraja-arumugam added community ✨ Community Contribution area-layout StackLayout, GridLayout, ContentView, AbsoluteLayout, FlexLayout, ContentPresenter labels Mar 18, 2026

sheiksyedm marked this pull request as ready for review March 19, 2026 08:52

Copilot AI review requested due to automatic review settings March 19, 2026 08:52

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kubaflo changed the base branch from main to inflight/current March 22, 2026 16:10

Merge branch 'inflight/current' into fix-34464

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🤖 AI Summary

Key Findings

Fix Candidates

Key Findings

Fix Candidates

Gate FAILEDResult:

Evidence

Gate Result: ✅ PASSED

Evidence

Gate FAILEDResult:

Evidence

Fix Candidates

Cross-Pollination

Gate FAILEDResult:

Evidence

✅ Final Recommendation: APPROVE

Phase Status

Summary

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Fix Quality

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