36 lines
1.5 KiB
Markdown
36 lines
1.5 KiB
Markdown
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## WPF InvalidCastException when displaying a checked MenuItem
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### Symptoms
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WPF throws an InvalidCastException when an application displays a MenuItem,
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provided the following conditions are all met:
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* The application is running on a server.
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* The MenuItem is checked (MenuItem.IsChecked = true).
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* The MenuItem is a sub-menu item (MenuItem.Role = SubmenuItem).
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* The MenuItem is a descendant of a RibbonWindow.
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* The RibbonWindow comes from the out-of-band ("toolkit") version of the WPF ribbon control library.
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The InvalidCastException's message is akin to
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Unable to cast object of type 'System.Windows.Style' to type 'System.Windows.Media.Geometry'
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and the callstack begins with
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at System.Windows.Shapes.Path.get_Data()
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at System.Windows.Shapes.Path.get_DefiningGeometry()
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at System.Windows.Shapes.Shape.GetNaturalSize()
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at System.Windows.Shapes.Shape.MeasureOverride()
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### Cause
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The exception is due to a resource key conflict between the ribbon library and the theme
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file for server machines (PresentationFramework.AeroLite.dll). Both declare resources
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using the same key. The theme file includes a DynamicResource reference intended to find
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the Geometry describing the MenuItem's checkmark, but in the circumstances described above
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the reference resolves to the ribbon library's resource. This effectively sets the value
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of Path.Data to an object of type Style. The next measure pass then encounters the exception.
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### Resolution
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The fix for this is expected in a future servicing update for Windows 10.
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### More information
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