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[leak-fix] Fix Border.StrokeDashArray memory leak (Fixes #35492) #36254

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kubaflo wants to merge 1 commit into from
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[leak-fix] Fix Border.StrokeDashArray memory leak (Fixes #35492) #36254

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19 changes: 15 additions & 4 deletions src/Controls/src/Core/Border/Border.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,11 +25,14 @@ public class Border : View, IContentView, IBorderView, IPaddingElement, ISafeAre
PropertyChangedEventHandler? _strokeShapeChanged;
WeakNotifyPropertyChangedProxy? _strokeProxy = null;
PropertyChangedEventHandler? _strokeChanged;
WeakNotifyCollectionChangedProxy? _strokeDashArrayProxy = null;
NotifyCollectionChangedEventHandler? _strokeDashArrayChanged;

~Border()
{
_strokeShapeProxy?.Unsubscribe();
_strokeProxy?.Unsubscribe();
_strokeDashArrayProxy?.Unsubscribe();
}

/// <summary>Bindable property for <see cref="Content"/>.</summary>
Expand Down Expand Up @@ -310,13 +313,21 @@ public float[]? StrokeDashPattern
{
get
{
if (StrokeDashArray is INotifyCollectionChanged oldCollection)
oldCollection.CollectionChanged -= OnStrokeDashArrayChanged;

_strokeDashPattern = StrokeDashArray?.ToFloatArray();

// Subscribe weakly so a shared/long-lived DoubleCollection does not strongly
// root this Border for the collection's lifetime. The proxy is torn down in
// ~Border(), mirroring the Stroke/StrokeShape weak proxies above.
if (StrokeDashArray is INotifyCollectionChanged newCollection)
newCollection.CollectionChanged += OnStrokeDashArrayChanged;
{
_strokeDashArrayChanged ??= OnStrokeDashArrayChanged;
_strokeDashArrayProxy ??= new();
_strokeDashArrayProxy.Subscribe(newCollection, _strokeDashArrayChanged);

@MauiBot MauiBot Jul 2, 2026

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🔍 AI-Generated Review (multi-model)

[moderate] Performance-Critical Path Optimization -- Avoid re-subscribing the weak collection proxy on every StrokeDashPattern read when the dash collection has not changed. WeakNotifyCollectionChangedProxy.Subscribe always detaches/re-attaches the event and replaces its source/handler WeakReferences, so each platform mapper read (including the read triggered by OnStrokeDashArrayChanged after every collection mutation) allocates additional weak references and churns event subscriptions. Guard with the current proxy source (for example, only call Subscribe when it is not already subscribed to newCollection) while still unsubscribing when the collection changes or becomes null.

}
else
{
_strokeDashArrayProxy?.Unsubscribe();
}

return _strokeDashPattern;
}
Expand Down
25 changes: 25 additions & 0 deletions src/Controls/tests/Core.UnitTests/BorderUnitTests.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,6 @@
#nullable enable
using System;
using System.Threading.Tasks;
using Xunit;

namespace Microsoft.Maui.Controls.Core.UnitTests
Expand Down Expand Up @@ -44,5 +46,28 @@ public void ChildrenHaveParentsWhenContentIsSet()
border.Content = null;
Assert.Null(label.Parent);
}

[Fact]
public async Task SharedStrokeDashArrayDoesNotLeakBorder()
{
// A shared / long-lived DoubleCollection, exactly as the issue describes
// (e.g. a static field or a value reused from a ResourceDictionary).
var sharedDashArray = new DoubleCollection { 2, 2 };

WeakReference weakBorder;
{
var border = new Border { StrokeDashArray = sharedDashArray };

// Reading StrokeDashPattern installs the CollectionChanged subscription,
// exactly as the platform border handler does when rendering the dash.
_ = border.StrokeDashPattern;

weakBorder = new WeakReference(border);
// Drop the only strong reference to `border`; `sharedDashArray` stays alive.
}

Assert.False(await weakBorder.WaitForCollect(), "Border should not be alive!");
GC.KeepAlive(sharedDashArray);
}
}
}
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