How to make add a fade-in/fade-out animation based on ViewModel property value?

Question

I have a ViewModel which exposes the string property PageToolBarVisible which can be true or false:

Answer 1

You can put the BeginStoryboard inside your DataTrigger.EnterActions

<DataTrigger Binding="{Binding PageToolBarVisible}" Value="false">
    <DataTrigger.EnterActions>
        <BeginStoryboard>
            <Storyboard>
                <DoubleAnimation
                Storyboard.TargetName="PageToolBar"
                Storyboard.TargetProperty="(TextBlock.Opacity)"
                From="0.0" To="1.0" Duration="0:0:3"/>
            </Storyboard>
        </BeginStoryboard>
    </DataTrigger.EnterActions>

    <DataTrigger.ExitActions>
        <BeginStoryboard>
            <Storyboard>
                <DoubleAnimation
                    Storyboard.TargetName="PageToolBar"
                    Storyboard.TargetProperty="(TextBlock.Opacity)"
                    From="1.0" To="0.0" Duration="0:0:3"/>
            </Storyboard>
        </BeginStoryboard>
    </DataTrigger.ExitActions>
</DataTrigger>