What does the WPF star do (Width="100*")

Question

What does exactly the star in size terms in WPF mean?

Answer 1

In a WPF Grid, Width="*" or Height="*" means proportional sizing.
For example: to give 30% to column 1 and 70% to column 2 -

<ColumnDefinition Width="3*" /> <ColumnDefinition Width="7*" /> 

And likewise for rows -

<RowDefinition Height="3*" /> <RowDefinition Height="7*" /> 

The numbers do not have to be integers.
If the Width for RowDefinition (Height for ColumnDefinition) is omitted, 1* is implied.
In this example, column 1 is 1.5 times wider than column 2 -

<ColumnDefinition Width="1.5*" /> <ColumnDefinition /> 

You can mix auto-fit and fixed widths with * (proportional) widths; in that case the * columns are apportioned to the remainder after the auto-fit and fixed widths have been calculated -

<Grid.ColumnDefinitions>     <ColumnDefinition Width="Auto" />  <!-- Auto-fit to content, 'Hi' -->     <ColumnDefinition Width="50.5" />  <!-- Fixed width: 50.5 device units) -->     <ColumnDefinition Width="69*" />   <!-- Take 69% of remainder -->     <ColumnDefinition Width="31*"/>    <!-- Take 31% of remainder --> </Grid.ColumnDefinitions> <TextBlock Text="Hi" Grid.Column="0" />