GridSplitter在WPF中调整大小

Question

我有一个有3行的网格。当我向下拖动到网格分割器时，网格分割器消失了。但我需要做＆＃34; auto＆＃34;第一行的高度。我该如何解决这个问题？

这是代码：

  <Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="20"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
    <StackPanel>
        <Border Background="BlueViolet" Height="20" Margin="3"/>
        <Border Background="BlueViolet" Height="20" Margin="3"/>
        <Border Background="BlueViolet" Height="20" Margin="3"/>
        <Border Background="BlueViolet" Height="20" Margin="3"/>
        <Border Background="BlueViolet" Height="20" Margin="3"/>
    </StackPanel>

    <GridSplitter Background="White" HorizontalAlignment="Stretch" Grid.Row="1" Height="5"/>
    <TextBlock IsHitTestVisible="False" Text="GridSplitter here.." Grid.Row="1" HorizontalAlignment="Center" VerticalAlignment="Center"/>

    <Border Background="CornflowerBlue" Grid.Row="2" Margin="3"/>        

</Grid>

感谢您的帮助。