将“从”和“到”属性绑定到控件高度

Question

Here is what I am attempting to do: I have a textblock (whose size isn't fixed) inside a grid. I want the grid's height to animate to the size of the textblock when the user presses a button, revealing all the content of the textblock.

This is the xaml with the grid and textblock (simplified):

<Grid x:Name="mygrid" ScrollViewer.VerticalScrollBarVisibility="Disabled" Height="38" Margin="10,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Top">
    <TextBlock MaxWidth="400" x:Name="mytextblock" HorizontalAlignment="Left" Margin="10,0" TextWrapping="WrapWholeWords" VerticalAlignment="Top" FontSize="10.667" Foreground="#BFFFFFFF" Text="reallylongtextgoeshere"/>
</Grid>

This is my current code:

<Storyboard x:Name="ExtendDescription">
    <DoubleAnimation x:Name="DBED" Duration="00:00:00.6" Storyboard.TargetProperty="Height" EnableDependentAnimation="True" From="0" To="{Binding ElementName=mytextblock, Path=ActualHeight}" Storyboard.TargetName="mygrid">
       <DoubleAnimation.EasingFunction>
            <CircleEase EasingMode="EaseInOut"/>
       </DoubleAnimation.EasingFunction>
    </DoubleAnimation>
</Storyboard>

I have spent the last hour or so looking for solutions, but nothing I've come up with has worked. Any idea on how I can get this working? For the moment the animation has the rather odd behavior of animating the height down to 0, making the grid smaller, instead of larger :/

Answer 1

In the end, I fixed this by handling this via C#. When the Textblock SizeChanged event fires, the following code gets executed:

myGrid.Visibility = Visibility.Visible;
DBED.To = DESCRIPTION.ActualHeight + 4;
DBED2.From = DESCRIPTION.ActualHeight + 4;

DBED and DBED2 being the DoubleAnimations. The +4 is simply to have a little margin, so that the text doesn't get clipped off.

I suspect handling this via xaml doesn't work because the ActualHeight property gets measured before anything is rendered, making it's value equals to 0.