<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition />
</Grid.RowDefinitions>
<ToggleButton
Grid.Row="0"
Width="40"
Height="22"
Margin="10,10,0,10"
HorizontalAlignment="Left">
<ToggleButton.Triggers>
<EventTrigger RoutedEvent="ToggleButton.Checked">
<BeginStoryboard>
<Storyboard Storyboard.TargetName="bule" Storyboard.TargetProperty="Width">
<DoubleAnimation
BeginTime="0:0:0"
From="0"
To="100"
Duration="0:0:0.5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
<EventTrigger RoutedEvent="ToggleButton.Unchecked">
<BeginStoryboard>
<Storyboard Storyboard.TargetName="bule" Storyboard.TargetProperty="Width">
<DoubleAnimation
BeginTime="0:0:0"
From="100"
To="0"
Duration="0:0:0.5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</ToggleButton.Triggers>
</ToggleButton>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<StackPanel
x:Name="bule"
Grid.Column="0"
Height="{Binding ElementName=stackPanel, Path=ActualHeight}"
Background="Blue" />
<StackPanel
Grid.Column="1"
Height="{Binding ActualHeight, ElementName=stackPanel}"
Background="Red" />
</Grid>
</Grid>
