#1,168 – Layout in Action, part V

When a panel is laying out its children, it will respect (make use of) an explicit size specified for a child control.

In the example below, the MyLabel control specifies a width of 100.  This makes it wider than it would normally be to fit its content.

    <StackPanel Margin="5" Background="Honeydew">
        <loc:MyLabel Content="Billy" HorizontalAlignment="Center" Width="100"
                     Background="Thistle" />

At run-time, the measure/arrange process is:

  • StackPanel reads the label’s desired width of 100, using this value as the “constrained” width (target width)
  • StackPanel calls Measure on the label, with constrained width of 100 and height of Infinity
  • Label returns a size from MeasureOverride with width and height equal to what’s required for its content (31.4 wide x 26 high)
  • StackPanel calls Arrange on MyLabel, passing in a size that includes the explicit width (100 x 26)