Fix CollectionView group header not stretching to full width on Windows#34710
Fix CollectionView group header not stretching to full width on Windows#34710
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The ListViewHeaderItem and GridViewHeaderItem styles in ItemsViewStyles.xaml had HorizontalContentAlignment set to Left and Padding of 12,8,12,0 which prevented group headers from stretching to match item width. Changed to HorizontalContentAlignment=Stretch with zero padding to match how regular item containers are configured. Preserved the 4px bottom margin for visual separation between headers and items. Fixes #23038 Fixes #16824 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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🚀 Dogfood this PR with:
curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34710Or
iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34710" |
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Pull request overview
Fixes a Windows-specific CollectionView grouped header layout issue by updating the default WinUI header container styles to allow header content to stretch full width, and adds a new UI regression test (HostApp page + Appium/NUnit test) for issue #23038.
Changes:
- Updated WinUI
ListViewHeaderItem/GridViewHeaderItemstyles to useHorizontalContentAlignment="Stretch"and remove default padding. - Added a HostApp reproduction page for a grouped
CollectionViewwith header/footer templates. - Added an Appium-based UI test validating group header width matches the item/footer width.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.
| File | Description |
|---|---|
| src/Controls/src/Core/Platform/Windows/CollectionView/ItemsViewStyles.xaml | Adjusts Windows header container defaults to allow group header templates to stretch full width. |
| src/Controls/tests/TestCases.HostApp/Issues/Issue23038.cs | Adds a grouped CollectionView scenario with header/footer templates and AutomationIds for testing. |
| src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue23038.cs | Adds an Appium UI test asserting header width stretches to match the CollectionView/item/footer width. |
| <Setter Property="Padding" Value="0,0,0,0" /> | ||
| <Setter Property="HorizontalContentAlignment" Value="Stretch" /> | ||
| <Setter Property="VerticalContentAlignment" Value="Top" /> | ||
| <Setter Property="MinHeight" Value="{ThemeResource ListViewHeaderItemMinHeight}" /> | ||
| <Setter Property="MinHeight" Value="0" /> |
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MinHeight for ListViewHeaderItem was changed from the platform theme resource to 0. This is unrelated to the width/stretching fix and risks regressing header sizing/touch target consistency. Consider keeping MinHeight as {ThemeResource ListViewHeaderItemMinHeight} (or justify why it must be 0).
| <Setter Property="HorizontalContentAlignment" Value="Stretch" /> | ||
| <Setter Property="VerticalContentAlignment" Value="Top" /> | ||
| <Setter Property="MinHeight" Value="{ThemeResource GridViewHeaderItemMinHeight}" /> | ||
| <Setter Property="MinHeight" Value="0" /> |
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MinHeight for GridViewHeaderItem was changed from the platform theme resource to 0. Unless this is required for the stretching fix, it likely causes an unintended UI regression (header height/touch target). Consider reverting to {ThemeResource GridViewHeaderItemMinHeight}.
| <Setter Property="MinHeight" Value="0" /> | |
| <Setter Property="MinHeight" Value="{ThemeResource GridViewHeaderItemMinHeight}" /> |
| label.SetBinding(Label.TextProperty, "Name"); | ||
| label.SetBinding(Label.AutomationIdProperty, "Name", stringFormat: "Header_{0}"); | ||
| return label; |
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The group header AutomationId is being generated from the bound Name value ("Team A"), which produces IDs containing spaces/underscores (e.g., Header_Team A). For UI test stability, prefer deterministic PascalCase AutomationIds without spaces (e.g., derive from a sanitized key or set explicit IDs).
| label.SetBinding(Label.TextProperty, "Count", stringFormat: "Total: {0}"); | ||
| label.SetBinding(Label.AutomationIdProperty, "Name", stringFormat: "Footer_{0}"); | ||
| return label; |
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The group footer AutomationId is being generated from the bound Name value ("Team A"), resulting in IDs with spaces (e.g., Footer_Team A). Consider using a sanitized key / explicit AutomationIds that follow the repo's UI test conventions (PascalCase, no spaces) to keep Appium selectors reliable.
| // Get the group header bounds | ||
| var headerRect = App.WaitForElement("Header_Team A").GetRect(); | ||
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| // Get the group footer bounds (footers are regular list items, they already stretch) | ||
| var footerRect = App.WaitForElement("Footer_Team A").GetRect(); |
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This test locates elements by AutomationIds containing spaces (e.g., "Header_Team A", "Footer_Team A"). These tend to be brittle across platforms/drivers; it would be more reliable to use sanitized/deterministic PascalCase AutomationIds (and update the HostApp page accordingly).
🧪 PR Test EvaluationOverall Verdict: The UI test covers the primary fix scenario (list-based grouped CollectionView header stretching) but misses coverage for the grid-based layout path that the fix also modifies.
📊 Expand Full EvaluationPR Test Evaluation ReportPR: #34710 — Fix CollectionView group header not stretching to full width on Windows Overall VerdictThe test validates the primary fix (header stretching to full width in list-based CollectionView), but the fix also modifies 1. Fix Coverage — ✅The fix changes
The test creates a grouped Minor gap: the 2. Edge Cases & Gaps —
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🚦 Gate - Test Before and After Fix📊 Expand Full Gate —
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| Test | Without Fix (expect FAIL) | With Fix (expect PASS) |
|---|---|---|
🖥️ Issue23038 Issue23038 |
✅ FAIL — 578s | ✅ PASS — 477s |
🔴 Without fix — 🖥️ Issue23038: FAIL ✅ · 578s
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VSTest version 18.0.1 (x64)
Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
D:\a\1\s\artifacts\bin\Controls.TestCases.WinUI.Tests\Debug\net10.0\Controls.TestCases.WinUI.Tests.dll
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in D:\a\1\s\artifacts\bin\Controls.TestCases.WinUI.Tests\Debug\net10.0\Controls.TestCases.WinUI.Tests.dll
NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 3/30/2026 10:30:31 PM FixtureSetup for Issue23038(Windows)
>>>>> 3/30/2026 10:30:40 PM GroupHeaderShouldStretchToFullWidth Start
>>>>> 3/30/2026 10:30:43 PM GroupHeaderShouldStretchToFullWidth Stop
>>>>> 3/30/2026 10:30:43 PM Log types:
Failed GroupHeaderShouldStretchToFullWidth [3 s]
Error Message:
Group header width should match group footer width
Assert.That(headerRect.Width, Is.EqualTo(footerRect.Width).Within(2))
Expected: 1008 +/- 2
But was: 984
Off by: 24.0d
Stack Trace:
at Microsoft.Maui.TestCases.Tests.Issues.Issue23038.GroupHeaderShouldStretchToFullWidth() in /_/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue23038.cs:line 33
1) at Microsoft.Maui.TestCases.Tests.Issues.Issue23038.GroupHeaderShouldStretchToFullWidth() in /_/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue23038.cs:line 33
NUnit Adapter 4.5.0.0: Test execution complete
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[xUnit.net 00:00:00.11] Discovering: Controls.TestCases.WinUI.Tests
[xUnit.net 00:00:00.32] Discovered: Controls.TestCases.WinUI.Tests
Total tests: 1
Failed: 1
Test Run Failed.
Total time: 34.2399 Seconds
🟢 With fix — 🖥️ Issue23038: PASS ✅ · 477s
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Running selected tests in D:\a\1\s\artifacts\bin\Controls.TestCases.WinUI.Tests\Debug\net10.0\Controls.TestCases.WinUI.Tests.dll
NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 3/30/2026 10:38:30 PM FixtureSetup for Issue23038(Windows)
>>>>> 3/30/2026 10:38:39 PM GroupHeaderShouldStretchToFullWidth Start
>>>>> 3/30/2026 10:38:42 PM GroupHeaderShouldStretchToFullWidth Stop
Passed GroupHeaderShouldStretchToFullWidth [2 s]
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[xUnit.net 00:00:00.14] Discovering: Controls.TestCases.WinUI.Tests
[xUnit.net 00:00:00.34] Discovered: Controls.TestCases.WinUI.Tests
Test Run Successful.
Total tests: 1
Passed: 1
Total time: 28.3320 Seconds
📁 Fix files reverted (2 files)
eng/pipelines/ci-copilot.ymlsrc/Controls/src/Core/Platform/Windows/CollectionView/ItemsViewStyles.xaml
🤖 AI Summary📊 Expand Full Review —
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| # | Source | Approach | Test Result | Files Changed | Notes |
|---|---|---|---|---|---|
| PR | PR #34710 | Change HorizontalContentAlignment to Stretch, Padding to 0, MinHeight to 0 on ListViewHeaderItem + GridViewHeaderItem |
✅ PASSED (Gate) | ItemsViewStyles.xaml |
Original PR; MinHeight change is controversial |
🔧 Fix — Analysis & Comparison
Fix Candidates
| # | Source | Approach | Test Result | Files Changed | Notes |
|---|---|---|---|---|---|
| 1 | try-fix (claude-opus-4.6) | Template-level override: hardcode HorizontalContentAlignment="Stretch" and Margin="0" on ContentPresenter in ControlTemplate, preserving all original setter values/theme resources |
✅ PASS | ItemsViewStyles.xaml (+4/-4 lines) |
More conservative than PR — preserves MinHeight and Padding theme resources |
| 2 | try-fix (claude-sonnet-4.6) | Setter-only: change Padding→0,0,0,0 + HorizontalContentAlignment→Stretch on both header item styles; keep MinHeight at {ThemeResource} unchanged; ControlTemplate untouched |
✅ PASS | ItemsViewStyles.xaml (+2/-2 lines) |
Minimal fix — proves MinHeight=0 is NOT needed; cleaner than PR |
| 3 | try-fix (gpt-5.3-codex) | Template StackPanel: set HorizontalAlignment="Stretch" on ControlTemplate's root StackPanel + ContentPresenter margin 0,8,0,0; no setter changes at all |
✅ PASS | ItemsViewStyles.xaml |
No setter modifications — purely template-level fix |
| 4 | try-fix (gpt-5.4, gemini unavailable) | C# runtime hook attempt (no viable hook found) + fallback: only HorizontalContentAlignment→Stretch setter, leaving Padding and MinHeight at theme resources |
❌ FAIL | ItemsViewStyles.xaml |
Confirms Padding=0 is REQUIRED alongside HorizontalContentAlignment=Stretch; stretch alone leaves 24px gap |
| PR | PR #34710 | Change HorizontalContentAlignment→Stretch, Padding→0,0,0,0, MinHeight→0 on both ListViewHeaderItem + GridViewHeaderItem style setters |
✅ PASSED (Gate) | ItemsViewStyles.xaml |
Original PR; MinHeight change is controversial |
Cross-Pollination
| Model | Round | New Ideas? | Details |
|---|---|---|---|
| claude-opus-4.6 | 2 | No | NO NEW IDEAS — solution space exhausted |
| claude-sonnet-4.6 | 2 | No | NO NEW IDEAS |
| gpt-5.3-codex | 2 | Yes | NEW IDEA: Bind ItemWidth explicitly through ItemContentControl context — overly complex, fragile, not pursued |
| gpt-5.4 | 2 | Yes | NEW IDEA: Use GroupStyle.HeaderContainerStyle via selector to stretch header containers in C# — more invasive than needed, not pursued given simpler PASS alternatives |
Exhausted: Yes — 3/4 models returned NO NEW IDEAS; 2 new ideas not viable given simpler passing solutions already found.
Selected Fix: Attempt 2 (Setter-only: Padding→0,0,0,0 + HorizontalContentAlignment→Stretch, keep MinHeight at theme resource) — Reason: Minimal, focused change to style setters only. Preserves theme resource MinHeight (addressing the main unresolved review comment). Proved by both Attempt 2 and Attempt 4's failure that both changes are required. The PR's MinHeight=0 change is unnecessary and was the primary concern in existing review feedback.
📋 Report — Final Recommendation
⚠️ Final Recommendation: REQUEST CHANGES
Phase Status
| Phase | Status | Notes |
|---|---|---|
| Pre-Flight | ✅ COMPLETE | Issues #23038, #16824; Windows only; 3 files changed |
| Gate | ✅ PASSED | Windows — tests fail without fix, pass with fix |
| Try-Fix | ✅ COMPLETE | 4 attempts: 3 PASS, 1 FAIL; cross-pollination exhausted |
| Report | ✅ COMPLETE |
Summary
The PR correctly fixes a long-standing Windows CollectionView bug where group headers did not stretch to full width. The fix to HorizontalContentAlignment=Stretch and Padding=0 is valid and necessary. However, the PR includes one change that is not needed for the fix and creates a regression risk: setting MinHeight=0 for both ListViewHeaderItem and GridViewHeaderItem. Try-Fix exploration confirms a minimal setter-only fix (Padding + HorizontalContentAlignment, without touching MinHeight) passes all tests identically.
Selected Fix: PR's fix — except the MinHeight=0 change should be reverted.
Root Cause
Two style setters on ListViewHeaderItem and GridViewHeaderItem in ItemsViewStyles.xaml caused the bug:
Padding="12,8,12,0"— the ControlTemplate bindsContentPresenter.MargintoPadding, shrinking the header horizontally by 24pxHorizontalContentAlignment="Left"— prevents the ContentPresenter from stretching to fill available width
Both must be fixed together (Attempt 4's failure proved that changing only alignment is insufficient).
Fix Quality
What's good:
- ✅ Correct root cause fix — both
Padding=0andHorizontalContentAlignment=Stretchare required and correctly applied to bothListViewHeaderItemandGridViewHeaderItem - ✅ Tests added with
[Category(UITestCategories.CollectionView)]and proper structure - ✅ Gate passed — test verifies the fix empirically
What needs to change:
1. 🚨 Revert MinHeight=0 for both styles (critical)
The MinHeight change from {ThemeResource ListViewHeaderItemMinHeight} (and GridViewHeaderItemMinHeight) to 0 is not needed for the stretch fix. Attempt 2 proved this: changing only Padding and HorizontalContentAlignment passes the test with MinHeight kept at the theme resource value.
Setting MinHeight=0 risks:
- Headers that are invisible/zero-height if content is empty or during layout passes
- Touch target regression (WinUI theme values ensure minimum interactive area)
- Potential visual regressions on different DPI scales
Suggested change (revert both MinHeight lines):
<!-- ListViewHeaderItem -->
<Setter Property="MinHeight" Value="{ThemeResource ListViewHeaderItemMinHeight}" />
<!-- GridViewHeaderItem -->
<Setter Property="MinHeight" Value="{ThemeResource GridViewHeaderItemMinHeight}" />2. ⚠️ AutomationId values contain spaces (medium)
The HostApp binds AutomationId from group names: Header_Team A and Footer_Team A contain spaces. These IDs with spaces can be unreliable across Appium drivers. Prefer sanitized PascalCase IDs (e.g., HeaderTeamA, FooterTeamA) or use fixed string constants.
3. ⚠️ Missing GridItemsLayout test coverage (low)
The fix modifies both ListViewHeaderItem (used for linear layout) and GridViewHeaderItem (used for GridItemsLayout). The test only exercises the linear layout path. A second test case with ItemsLayout = new GridItemsLayout(2, ItemsLayoutOrientation.Vertical) would provide complete coverage.
4. ℹ️ Branch consideration
The PR description notes this may be a breaking change and asks about targeting net11.0. Since MinHeight is being changed from a theme value to 0, this could affect existing apps relying on the default header height. Reverting the MinHeight change would reduce the breaking surface and make the fix suitable for main.
MauiBot
added
s/agent-changes-requested
…lish - Revert MinHeight to theme resources for ListViewHeaderItem and GridViewHeaderItem (unrelated to the stretching fix) - Use PascalCase AutomationIds without spaces for group headers/footers by adding a Key property to the team model - Update XAML comments to reflect full scope of style customizations - Remove redundant WaitForElement call and add tolerance explanation - Update UI test to reference the sanitized AutomationIds Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
🧪 PR Test EvaluationOverall Verdict: ✅ Tests are adequate The test directly validates the fix — it verifies that group headers stretch to the full CollectionView width on Windows, which is exactly what the XAML style change achieves.
📊 Expand Full EvaluationPR Test Evaluation ReportPR: #34710 — [Windows] CollectionView group header not stretching to full width Overall Verdict✅ Tests are adequate The test exercises the exact behavior fixed by the PR: it measures group header and footer widths to confirm the header now stretches to full CollectionView width, which directly reflects the 1. Fix Coverage — ✅The fix changes The test:
The test would fail without the fix (header stays 2. Edge Cases & Gaps —
|
| Fix | Test | |
|---|---|---|
| Control | ListViewHeaderItem / GridViewHeaderItem (Windows XAML) |
Grouped CollectionView header on Windows |
| Property | HorizontalContentAlignment: Left → Stretch |
Header width == full CollectionView width |
| Would fail without fix? | ✅ Yes — header stays narrow | ✅ Yes — headerRect.Width != footerRect.Width |
Recommendations
- (Optional) Add a second assertion for
HeaderTeamB/FooterTeamBto verify all groups are affected, not just the first. - (Optional) Consider a brief comment in the test explaining why the footer is used as the "full width" baseline — it's a non-obvious but correct approach.
- (Non-blocking) The
GridViewHeaderItemstyle fix is untested (no test usesItemsLayout = GridItemsLayout). Not strictly required since the root cause is the same, but worth noting.
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Description of Change
The ListViewHeaderItem and GridViewHeaderItem styles in ItemsViewStyles.xaml had HorizontalContentAlignment set to Left and Padding of 12,8,12,0 which prevented group headers from stretching to match item width.
Changed to HorizontalContentAlignment=Stretch with zero padding to match how regular item containers are configured. Preserved the 4px bottom margin for visual separation between headers and items.
As this is a breaking change i think we might want to net11.0 ?
Issues Fixed
Fixes #23038
Fixes #16824