根据Expander的IsExpanded属性值的变化动态设计Control的size

简要说明：

当Expander 的IsExpanded属性为“True” 时给控件设个尺寸（此处为高度），当为“False”时给控件设另外一个值。

知识点：数据绑定、Style和Trigger

      <Grid>         <Grid.RowDefinitions>             <RowDefinition>                 <RowDefinition.Style>                     <Style TargetType="RowDefinition">                         <Setter Property="Height" Value="25" />                         <Style.Triggers>                             <DataTrigger Binding="{Binding ElementName=testExpander,Path=IsExpanded}" Value="True">                                 <Setter Property="Height" Value="205" />                             </DataTrigger>                         </Style.Triggers>                     </Style>                 </RowDefinition.Style>             </RowDefinition>             <RowDefinition Height="*" />         </Grid.RowDefinitions>         <Expander Header="Haha"  x:Name="testExpander" />         <StackPanel Grid.Row="1" >             <TabControl>                 <TabItem Header="HaHaTabItem" >                     <ListBox>                         <ListBoxItem Content="Blue" />                         <ListBoxItem Content="Black" />                         <ListBoxItem Content="Red" />                     </ListBox>                  </TabItem>             </TabControl>         </StackPanel>     </Grid>