[Breaking change]: WPF throws MC3063 error for empty ColumnDefinitions or RowDefinitions #47743
Description
Description
Starting with .NET 10 Preview 5, WPF applications will fail to build if <Grid.ColumnDefinitions> or <Grid.RowDefinitions> are declared but left empty in XAML. This results in error MC3063, indicating that the property does not have a value.
Previously, such declarations were allowed and did not cause build failures. Although empty ColumnDefinitions or RowDefinitions have minimal impact on the UI—since WPF defaults to a single row and column—all child elements are placed in that single cell unless otherwise specified.
Version
.NET 10 Preview 5
Previous behavior
WPF applications with empty <Grid.ColumnDefinitions> or <Grid.RowDefinitions> compiled successfully, even though the layout definitions were incomplete.
Example:
<Grid>
<Grid.ColumnDefinitions>
</Grid.ColumnDefinitions>
</Grid>New behavior
The same code now fails to compile with the following error:
Example:
error MC3063: Property 'ColumnDefinitions' does not have a value.
Type of breaking change
- Binary incompatible: Existing binaries might encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
- Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code might require source changes to compile successfully.
- Behavioral change: Existing binaries might behave differently at run time.
Reason for change
This change is a direct consequence of our efforts to support Grid XAML Shorthand Syntax (dotnet/wpf#9802). The PR that caused this change: dotnet/wpf#10866
Recommended action
Ensure that all <Grid.ColumnDefinitions> and <Grid.RowDefinitions> contains at least one valid or element.
Corrected example:
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
</Grid.ColumnDefinitions>
</Grid>Feature area
Windows Presentation Foundation (WPF)
Affected APIs
No response