Expander collapse animation not work - wpf

Question

I have implement some animation on Expander.Expanded and this work fine, but similar one does not work on Expander.Collapsed.
XAML:
<Border Name="bor3" >
<Border.Triggers>
<EventTrigger RoutedEvent="Expander.Expanded" SourceName="exp3">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
From="0"
To="1"
Duration="0:0:0.25"
Storyboard.TargetName="gr3"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
<EventTrigger RoutedEvent="Expander.Collapsed" SourceName="exp3" >
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
From="1"
To="0"
Duration="0:0:0.25"
Storyboard.TargetName="gr3"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Border.Triggers>
<Expander Name="exp3">
<Grid Name="gr3">
<Grid.LayoutTransform>
<ScaleTransform ScaleX="1" ScaleY="0"/>
</Grid.LayoutTransform>
<TextBlock >Test!</TextBlock>
</Grid>
</Expander>
</Border>
UPDATE:
I've test Datatriggers beside control Style but that has a same problem:
<Border Name="bor3" >
<Expander Name="exp3">
<Grid Name="gr3">
<Grid.Style>
<Style TargetType="Grid">
<Style.Triggers>
<DataTrigger Binding="{Binding IsExpanded, RelativeSource={RelativeSource AncestorType=Expander}}" Value="true">
<DataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
From="0"
To="1"
Duration="0:0:0.25"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
<DataTrigger.ExitActions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
From="1"
To="0"
Duration="0:0:0.25"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
</BeginStoryboard>
</DataTrigger.ExitActions>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
<Grid.LayoutTransform>
<ScaleTransform ScaleX="1" ScaleY="0"/>
</Grid.LayoutTransform>
<TextBlock >Test!</TextBlock>
</Grid>
</Expander>
</Border>
What is the problem and What is the solution?!

Answer 1

Before the collapse animation played his parent (ExpandSite ContentPresenter) becomes invisible. so we must make it visible before the collapse animation played:
XAML:
<Border Name="bor3" VerticalAlignment="Top" >
<Expander Name="exp3" Collapsed="exp3_Collapsed" >
<Expander.Resources>
<Storyboard x:Key="sbCollapse" >
<DoubleAnimation Storyboard.TargetName="gr3"
From="1"
To="0"
Duration="0:0:0.5"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
<Storyboard x:Key="sbExpand" >
<DoubleAnimation Storyboard.TargetName="gr3"
From="0"
To="1"
Duration="0:0:0.5"
Storyboard.TargetProperty="(FrameworkElement.LayoutTransform).(ScaleTransform.ScaleY)"/>
</Storyboard>
</Expander.Resources>
<Expander.Triggers>
<EventTrigger RoutedEvent="Expander.Expanded">
<BeginStoryboard Storyboard="{StaticResource sbExpand}" />
</EventTrigger>
</Expander.Triggers>
<Grid Name="gr3" Background="Green" Height="100">
<Grid.LayoutTransform>
<ScaleTransform ScaleX="1" ScaleY="0"/>
</Grid.LayoutTransform>
<TextBlock FontSize="40">Test!</TextBlock>
</Grid>
</Expander>
</Border>
Code:
private void exp3_Collapsed(object sender, RoutedEventArgs e)
{
var r = exp3.Template.FindName("ExpandSite", exp3) as UIElement;
r.Visibility = System.Windows.Visibility.Visible;
var sb1 = (Storyboard)exp3.FindResource("sbCollapse");
sb1.Begin();
}
;)