When a Grid in a StackPanel, the <Grid.RowDefininations> work abnormally about microsoft-ui-xaml

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[kmgallahan]

Per the Star sizing documentation:

https://learn.microsoft.com/en-us/windows/windows-app-sdk/api/winrt/microsoft.ui.xaml.gridlength?view=windows-app-sdk-1.5#star-sizing

Star sizing is a convention whereby a GridLength has a number value that specifies a weighted factor versus other GridLength values. Any GridLength values that use star sizing divide the available space, accounting for the weighting factors, and evaluating after any fixed widths are applied.

Per documentation on StackPanel usage:

https://learn.microsoft.com/en-us/windows/apps/design/layout/layouts-with-xaml#layout-panels

Stretch values for HorizontalAlignment/VerticalAlignment are respected in the direction opposite the Orientation property. If an element's size is not set explicitly, it stretches to fill the available width (or height if the Orientation is Horizontal). In the direction specified by the Orientation property, an element sizes to its content.

StackPanel.Orientation default value is Vertical. So your Grid is being vertically sized to its content in the StackPanel, which is nothing, so the Grid asks for and receives no vertical space from the StackPanel during layout, so the star sizing has no available space to divide up, hence the rows have no height.

If you give the Grid some amount of Height or provide content that asks for some amount of Height, then the StackPanel will provide said height and star sizing will have something to work with. Note that content in a single row requesting Height of 400 means the grid asks its parent for 400 Height, gets it, uses it for that row, and the stars are still left with nothing to work with.

A Grid inside a Grid asks for a whatever vertical Stretching will provide (the default value for Height), and the parent Grid is also asking to Stretch, so it gets the full Height, provides the Height to the child Grid, and the child grid uses said Height to divide amongst the Star sized rows after fixed height rows are accounted for.

[CTimet]

Ok I got it