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Clear IsThemeDictionary flag when ResourceDictionary gains an owner #11727

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Clear IsThemeDictionary flag when ResourceDictionary gains an owner #11727

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69eb98e
Clear IsThemeDictionary flag when ResourceDictionary gains an owner
amarinov-msft Jun 17, 2026
56d94d5
Add unit test for IsThemeDictionary flag clearing in ResourceDictiona…
amarinov-msft Jun 18, 2026
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12 changes: 12 additions & 0 deletions src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/ResourceDictionary.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1508,6 +1508,10 @@ internal void AddOwner(DispatcherObject owner)
fe.ShouldLookupImplicitStyles = true;
}

// Owned dictionaries are never theme dictionaries; clear the flag the ctor may
// have inherited from SystemResources.IsSystemResourcesParsing. Propagates to merged dictionaries.
IsThemeDictionary = false;
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_ownerFEs.Add(fe);
}
else
Expand All @@ -1530,6 +1534,10 @@ internal void AddOwner(DispatcherObject owner)
fce.ShouldLookupImplicitStyles = true;
}

// Owned dictionaries are never theme dictionaries; clear the flag the ctor may
// have inherited from SystemResources.IsSystemResourcesParsing. Propagates to merged dictionaries.
IsThemeDictionary = false;

_ownerFCEs.Add(fce);
}
else
Expand Down Expand Up @@ -1557,6 +1565,10 @@ internal void AddOwner(DispatcherObject owner)
// An Application ResourceDictionary can be accessed across threads
CanBeAccessedAcrossThreads = true;

// Owned dictionaries are never theme dictionaries; clear the flag the ctor may
// have inherited from SystemResources.IsSystemResourcesParsing. Propagates to merged dictionaries.
IsThemeDictionary = false;

// Seal all the styles and templates in this app dictionary
SealValues();
}
Expand Down
16 changes: 16 additions & 0 deletions ...Wpf/tests/UnitTests/PresentationFramework.Tests/System/Windows/ResourceDictionaryTests.cs
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Expand Up @@ -2,6 +2,7 @@
// The .NET Foundation licenses this file to you under the MIT license.

using System.Linq;
using System.Reflection;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Threading;
Expand Down Expand Up @@ -159,4 +160,19 @@ public void DynamicResource_ShouldRemainLastValue_WhenLocalResourceRemoved()
// The default foreground color of textBlock (as in aero2)
textBlock.Foreground.Should().BeSameAs(Brushes.Black);
}

[WpfFact]
public void AddOwner_ClearsInheritedIsThemeDictionaryFlag()
{
// Simulate a ResourceDictionary whose ctor inherited
// IsThemeDictionary from SystemResources.IsSystemResourcesParsing.
PropertyInfo isThemeDictionary = typeof(ResourceDictionary).GetProperty(
"IsThemeDictionary", BindingFlags.Instance | BindingFlags.NonPublic)!;
var rd = new ResourceDictionary();
isThemeDictionary.SetValue(rd, true);

_ = new Button { Resources = rd };

isThemeDictionary.GetValue(rd).Should().Be(false);
}
}