Begin a StoryBoard when IsOpen property of a Popup is set to True

How to Begin a StoryBoard when IsOpen property of a Popup is set to True?

ex:

<EventTrigger RoutedEvent="{Binding IsOpen, ElementName=pop}">
    <BeginStoryboard>
        <Storyboard>
            <DoubleAnimation Storyboard.TargetName="pop"
                             Storyboard.TargetProperty="Height"
                             Duration="0:0:1"
                             From="0.0"
                             To="20开发者_如何学运维0" />
            <DoubleAnimation Storyboard.TargetName="pop"
                             Storyboard.TargetProperty="Width"
                             Duration="0:0:1"
                             From="0.0"
                             To="{Binding ElementName=root,Path=ActualWidth}" />
        </Storyboard>
    </BeginStoryboard>
</EventTrigger>

I know EventTrigger RoutedEvent="{Binding IsOpen, ElementName=pop} is not ok

Thank you!

Since you did not mark for Answer, I assumed you still need some help in this. Here is a code snippet that will work your way (as per H.B.'s post)

<Window x:Class="WpfTestApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Window.Resources>
    <Style x:Key="PopupStyle" TargetType="{x:Type Popup}">
        <Style.Triggers>
            <Trigger Property="IsOpen" Value="True">
                <Trigger.EnterActions>
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation 
                                     Storyboard.TargetProperty="Height"
                                     Duration="0:0:1"
                                     From="0.0"
                                     To="200" />
                            <DoubleAnimation 
                                     Storyboard.TargetProperty="Width"
                                     Duration="0:0:1"
                                     From="0.0"
                                     To="500" />
                        </Storyboard>
                    </BeginStoryboard>
                </Trigger.EnterActions>
            </Trigger>
        </Style.Triggers> 

    </Style>
</Window.Resources>
<Grid>
    <Button Content="Button" Height="29" HorizontalAlignment="Left" Margin="24,19,0,0" Name="button1" VerticalAlignment="Top" Width="90" Click="button1_Click" />
    <Popup Name="pop" Style="{StaticResource PopupStyle}" >
        <Grid Background="Red">
            <TextBlock Text="I am in pop up" />
        </Grid>
    </Popup>
</Grid>

and the button click event handler in code behind to open the pop up..

 private void button1_Click(object sender, RoutedEventArgs e)
    {
        pop.PlacementTarget = (Button)sender;
        pop.IsOpen = true;
    }

1. Create a Style for the Popup.
2. Trigger on IsOpen -> true
3. Use Trigger.EnterActions to start a storyboard.