[iOS] Fix ObjectDisposedException in ContentView.RemoveContentMask by Oxymoron290 · Pull Request #34680 · dotnet/maui

Oxymoron290 · 2026-03-26T17:53:52Z

Description

Fixes an ObjectDisposedException crash in ContentView.RemoveContentMask() on iOS/MacCatalyst when the underlying CAShapeLayer (_contentMask) has already been deallocated by the native runtime during view hierarchy teardown.

The Problem

During view lifecycle teardown, WillRemoveSubview() calls RemoveContentMask(), which calls RemoveFromSuperLayer() on _contentMask. When iOS has already collected the native CAShapeLayer, the managed wrapper's Handle is IntPtr.Zero, calling any method on it throws ObjectDisposedException.

This is a manifestation of the long-standing iOS binding lifecycle issue documented in dotnet/macios#10562, where dealloc of a UIView calls RemoveFromSuperview() for every child while the native object is being deallocated, causing managed code to interact with already-disposed native objects.

Crash stack:

ObjectDisposedException: Cannot access a disposed object.
Object name: 'Microsoft.Maui.Platform.StaticCAShapeLayer'.
   at ObjCRuntime.NativeObjectExtensions.GetNonNullHandle(INativeObject, String)
   at CoreAnimation.CALayer.RemoveFromSuperLayer()
   at Microsoft.Maui.Platform.ContentView.RemoveContentMask()
   at Microsoft.Maui.Platform.ContentView.WillRemoveSubview(UIView)

The Fix

Added a disposal guard in RemoveContentMask() checking _contentMask.Handle != IntPtr.Zero before calling RemoveFromSuperLayer(). This follows the established pattern used throughout the codebase in ViewRenderer.cs, LayoutFactory2.cs, CellRenderer.cs, SkiaGraphicsView.cs, etc.

Related Work

UIView/GC: accessing Superview inside WillMoveToSuperview crashes app macios#10562 (upstream iOS binding lifecycle issue)
Avoid KVO on CALayer by introducing an Apple PlatformInterop #30861, [iOS] Fix MauiCALayer and StaticCAShapeLayer crash on finalizer thread #33818 (prior iOS disposal safety fixes in MAUI)

Testing

Added device test RemoveContentMaskDoesNotThrowWhenDisposed that:

Creates a ContentView with an active clip mask
Asserts the mask was created as a CAShapeLayer
Disposes the native handle (simulating iOS deallocation) and asserts Handle == IntPtr.Zero
Verifies RemoveFromSuperview() does not throw

Check Handle != IntPtr.Zero before calling RemoveFromSuperLayer() on _contentMask to prevent ObjectDisposedException when iOS has already deallocated the underlying CAShapeLayer during view hierarchy teardown. This follows the established disposal guard pattern used throughout the codebase (ViewRenderer.cs, LayoutFactory2.cs, CellRenderer.cs, etc.). Fixes a crash reported in Active Trader Pro on iOS/MacCatalyst where WillRemoveSubview triggers RemoveContentMask after the native layer has been collected. Related: dotnet#30861, dotnet#33818 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-03-26T17:54:03Z

🚀 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 -- 34680

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34680"

dotnet-policy-service · 2026-03-26T17:54:15Z

Hey there @@Oxymoron290! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

Copilot

Pull request overview

Fixes an iOS/MacCatalyst ObjectDisposedException when tearing down ContentView by guarding RemoveContentMask() against invoking RemoveFromSuperLayer() on a disposed CAShapeLayer.

Changes:

Add a native-handle guard before removing the _contentMask layer from its superlayer.
Add an iOS device regression test that simulates native mask deallocation and asserts removal does not throw.
Add minimal clip/shape stubs to force mask creation during the test.

Reviewed changes

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

File	Description
src/Core/src/Platform/iOS/ContentView.cs	Adds a `Handle != IntPtr.Zero` guard before calling `RemoveFromSuperLayer()` on `_contentMask`.
src/Core/tests/DeviceTests/Handlers/ContentView/ContentViewTests.iOS.cs	Adds a device regression test and local stubs to reproduce the disposed-mask scenario.

src/Core/tests/DeviceTests/Handlers/ContentView/ContentViewTests.iOS.cs

Copilot · 2026-03-26T17:57:11Z

src/Core/tests/DeviceTests/Handlers/ContentView/ContentViewTests.iOS.cs

+			public Paint Stroke { get; set; }
+			public double StrokeThickness { get; set; } = 1;
+			public LineCap StrokeLineCap { get; set; }
+			public LineJoin StrokeLineJoin { get; set; }
+			public float[] StrokeDashPattern { get; set; }


This stub introduces non-nullable reference-type properties (Paint Stroke and float[] StrokeDashPattern) without initialization, which can produce nullable-analysis warnings (and may fail builds if warnings are treated as errors). Initialize them to safe defaults or mark them nullable (e.g., Paint? / float[]?) to keep the test project warning-clean.

Suggested change

public Paint Stroke { get; set; }

public double StrokeThickness { get; set; } = 1;

public LineCap StrokeLineCap { get; set; }

public LineJoin StrokeLineJoin { get; set; }

public float[] StrokeDashPattern { get; set; }

public Paint? Stroke { get; set; }

public double StrokeThickness { get; set; } = 1;

public LineCap StrokeLineCap { get; set; }

public LineJoin StrokeLineJoin { get; set; }

public float[]? StrokeDashPattern { get; set; }

src/Core/src/Platform/iOS/ContentView.cs

- Replace conditional mask disposal with Assert.IsType<CAShapeLayer> to fail fast if the mask is not created (avoids false-positive) - Assert Handle == IntPtr.Zero after disposal to verify test setup - Remove customer issue link from test comment - Add reference to upstream dotnet/macios#10562 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

PureWeen · 2026-03-27T13:19:04Z

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

azure-pipelines · 2026-03-27T13:19:21Z

Azure Pipelines successfully started running 2 pipeline(s).

Assert.IsType<CAShapeLayer> requires an exact type match, but _contentMask is typed as StaticCAShapeLayer (a subclass of CAShapeLayer). This caused the RemoveContentMaskDoesNotThrowWhenDisposed test to fail on iOS and MacCatalyst with: 'Assert.IsType() Failure: Value is not the exact type' Also improve Assert.True to Assert.Equal for better diagnostic output on failure. Fixes: net10.0 iOS/MacCatalyst Helix Tests (Mono) device test failures Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

PureWeen · 2026-03-30T00:25:38Z

/azp run maui-pr-devicetests

azure-pipelines · 2026-03-30T00:25:52Z

Azure Pipelines successfully started running 1 pipeline(s).

…ison Assert.Equal(IntPtr.Zero, mask.Handle) fails on Apple TFMs because mask.Handle returns nint (NativeHandle) and xUnit's overload resolution falls through to Assert.Equal<DateTime>, producing CS1503. Use Assert.True with equality check instead. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

PureWeen · 2026-03-30T13:45:02Z

/azp run maui-pr-devicetests

azure-pipelines · 2026-03-30T13:45:19Z

Azure Pipelines successfully started running 1 pipeline(s).

On real iOS/MacCatalyst devices, calling Dispose() on a CAShapeLayer does not zero its Handle while another native reference (Layer.Mask) still retains it. Clear the native reference first to properly simulate iOS deallocating the layer during view teardown. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

With content.Layer.Mask cleared before Dispose(), the native retain count drops to zero and Handle is properly zeroed. Re-add the assertion to verify the guard condition is actually being tested. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Instead of relying on platform-specific Dispose() behavior (which varies depending on native retain counts), create a fresh CAShapeLayer with no native retains, Dispose it (deterministically zeroing Handle), then inject it into the private _contentMask field via reflection. This guarantees Handle == IntPtr.Zero on all platforms and directly tests the production guard in RemoveContentMask(). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

PureWeen · 2026-03-30T16:12:44Z

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

azure-pipelines · 2026-03-30T16:13:02Z

Azure Pipelines successfully started running 2 pipeline(s).

PureWeen · 2026-03-30T18:03:18Z

/backport to release/10.0.1xx-sr3

github-actions · 2026-03-30T18:03:29Z

Started backporting to release/10.0.1xx-sr3 (link to workflow run)

Copilot AI review requested due to automatic review settings March 26, 2026 17:53

dotnet-policy-service bot added the community ✨ Community Contribution label Mar 26, 2026

Copilot started reviewing on behalf of Oxymoron290 March 26, 2026 17:54 View session

Copilot AI reviewed Mar 26, 2026

View reviewed changes

Oxymoron290 marked this pull request as draft March 26, 2026 18:13

PureWeen reviewed Mar 27, 2026

View reviewed changes

src/Core/src/Platform/iOS/ContentView.cs Show resolved Hide resolved

github-actions bot mentioned this pull request Mar 27, 2026

[repo-status] Daily Repo Status - March 27, 2026 #34694

Closed

Oxymoron290 marked this pull request as ready for review March 27, 2026 12:22

Oxymoron290 and others added 3 commits March 30, 2026 10:56

github-actions bot mentioned this pull request Mar 30, 2026

[release/10.0.1xx-sr3] [iOS] Fix ObjectDisposedException in ContentView.RemoveContentMask #34744

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Oxymoron290 commented Mar 26, 2026 •

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