#1,166 – Layout in Action, part III

Layout in WPF dictates how layout panels (containers) arrange their child elements.  In the example below, we build on an earlier example to show how the measure and arrange phases work when host a Label in control in a StackPanel and then stretch the label.

Suppose the we have the XAML shown below. Note that the HorizontalAlignment of the Label is set to Stretch.

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

At run-time this looks like:

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

• StackPanel calls Measure on MyLabel
• Base Label class calculates how much space it needs (31.4 x 26) and MyLabel returns this value from MeasureOverride
• StackPanel decides to give the label the requested height, but stretches out its width
• StackPanel calls Arrange on MyLabel, passing in size of 164 x 26
• MyLabel.ArrangeOverride receives this value, passing on to base Label class
• Base Label class uses this size to know how to render label

Here’s some run-time output showing these values: