Empty ColumnDefinitions and RowDefinitions are disallowed

Starting with .NET 10, WPF applications fail to build if <Grid.ColumnDefinitions> or <Grid.RowDefinitions> are declared but left empty in XAML. This results in error MC3063, which indicates that the property doesn't have a value.

Version introduced

.NET 10

Previous behavior

Previously, WPF applications with empty <Grid.ColumnDefinitions> or <Grid.RowDefinitions> compiled successfully, even though the layout definitions were incomplete. The layout defaulted to a single row and column, placing all child elements in that single cell unless otherwise specified.

Example that previously compiled:

<Grid>
  <Grid.ColumnDefinitions>
  </Grid.ColumnDefinitions>
</Grid>

New behavior

Starting in .NET 10, the same code now fails to compile with the following error:

error MC3063: Property 'ColumnDefinitions' does not have a value.

This occurs when <Grid.ColumnDefinitions> or <Grid.RowDefinitions> elements are declared but contain no child <ColumnDefinition /> or <RowDefinition /> elements.

Type of breaking change

This change can affect source compatibility.

Reason for change

This change is a direct consequence of implementing Grid XAML Shorthand Syntax support.

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>

Affected APIs

None.