简单例子

代码

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="20"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Expander
            Grid.Row="1"
            Name="myExpander"
            Width="100"
            HorizontalAlignment="Center"
            Background="Tan"
            ExpandDirection="Down"
            Header="My Expander"
            IsExpanded="True" >
            <TextBlock TextWrapping="Wrap">
                You can set the content area of an Expander control to expand in one
                of four directions (Down, Up, Left, or Right) by using the
                ExpandDirection property. When the content area is collapsed,
                only the ExpanderHeader and its toggle button appear. A Button
                control that displays a directional arrow is used as a toggle button
                to expand or collapse the content area. When expanded, the Expander
                tries to display all of its content in a window-like area.
            </TextBlock>
        </Expander>
    </Grid>

效果