问如何在WPF中创建可折叠面板

EN

 <Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="2*"/>
    </Grid.RowDefinitions>
    <Border  Background="Red" Height="12" VerticalAlignment="Top" MouseEnter="StackPanel_MouseEnter" MouseLeave="StackPanel_MouseLeave"></Border>
</Grid>    

 private void StackPanel_MouseEnter(object sender, MouseEventArgs e)
    {
        Border sp = sender as Border;
        DoubleAnimation db = new DoubleAnimation();
        //db.From = 12;
        db.To = 150;
        db.Duration = TimeSpan.FromSeconds(0.5);
        db.AutoReverse = false;
        db.RepeatBehavior = new RepeatBehavior(1);
        sp.BeginAnimation(StackPanel.HeightProperty, db);
    }

    private void StackPanel_MouseLeave(object sender, MouseEventArgs e)
    {
        Border sp = sender as Border;
        DoubleAnimation db = new DoubleAnimation();
        //db.From = 12;
        db.To = 12;
        db.Duration = TimeSpan.FromSeconds(0.5);
        db.AutoReverse = false;
        db.RepeatBehavior = new RepeatBehavior(1);
        sp.BeginAnimation(StackPanel.HeightProperty, db);
    }
}