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Beginning with .NET 10 Preview 4, applications using DynamicResource incorrectly now crash at runtime.
Version introduced
.NET 10 Preview 4
Previous behavior
Applications that incorrectly initialized DynamicResource would continue running without crashing. The values would fall back to defaults, and an InvalidOperationException would appear in the output.
New behavior
Applications now crash with an error similar to the following:
System.Windows.Markup.XamlParseException: Set property 'System.Windows.ResourceDictionary.Source' threw an exception.
This occurs when an incorrect resource type is used with DynamicResource. For example, the code snippet below causes a crash because a SolidColorBrush is used instead of System.Windows.Media.Color:
<SolidColorBrush x:Key="RedColorBrush" Color="#FFFF0000" />
<SolidColorBrush x:Key="ResourceName" Color="{DynamicResource RedColorBrush}" />
Type of breaking change
This is both a source-incompatible and behavioral change.
Reason for change
This change improves the performance of DynamicResource usage. The optimization ensures that incorrect resource initialization is caught immediately, preventing unintended behavior.
Recommended action
To avoid crashes, ensure that the correct resource types are used with DynamicResource. For example, the following code resolves the issue by using System.Windows.Media.Color instead of SolidColorBrush:
<Color x:Key="RedColor">#FFFF0000</Color>
<SolidColorBrush x:Key="ResourceName" Color="{DynamicResource RedColor}" />
Affected APIs
None.
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