#1,165 – Layout in Action, part II

Layout in WPF dictates how layout panels (containers) arrange their child elements.  Below is a simple example of a StackPanel containing a custom Label that we’ve instrumented so that we can see when its Measure and Arrange methods are called.  (MyPanel derives from Label).

Suppose we use the label as follows:

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

The label looks like this at run-time:

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 space that it needs/wants
• StackPanel calls Arrange on MyLabel, passing in size of 31.4 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: