Time Delay on Trigger

Question

I wish to attach a time delay to a mouseover event on a WPF expander I have on my form (xaml supported by VB.NET code behind). This mouseover event essentially triggers the

Answer 1

Use an EventTrigger on the MouseOver event and a Storyboard with a BooleanAnimationUsingKeyFrames instead. In the Timeline of the Storyboard, you could have KeyFrames, so that the animation waits for some time before it affects the properties you want to change.

Answer 2

This was the code I settled on - based on the ideas already given:

    <Style x:Key="HoverExpander" TargetType="{x:Type Expander}">            
        <Style.Setters>                
            <Setter Property="IsExpanded" Value="False"/><!-- Initially collapsed -->            
        </Style.Setters>

        <Style.Triggers>
            <!-- Impose a short delay (500ms) before expanding control -->
            <EventTrigger RoutedEvent="Expander.MouseEnter">
                <BeginStoryboard>
                    <Storyboard>
                        <BooleanAnimationUsingKeyFrames
                            Storyboard.TargetProperty="IsExpanded"
                            Duration="0:0:0.5">
                            <DiscreteBooleanKeyFrame Value="True" KeyTime="100%"/><!-- I.E. after 500ms -->                             
                        </BooleanAnimationUsingKeyFrames>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
            <!-- Collapse when mouse leaves control-->
            <EventTrigger RoutedEvent="Expander.MouseLeave">
                <BeginStoryboard>
                    <Storyboard>
                        <BooleanAnimationUsingKeyFrames
                            Storyboard.TargetProperty="IsExpanded"
                            Duration="0:0:0.1">
                            <DiscreteBooleanKeyFrame Value="False" KeyTime="0%"/><!-- I.E. Immediately -->

                        </BooleanAnimationUsingKeyFrames>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Style.Triggers>
    </Style>

Then apply as before. This was tested and works in .NET 4.0. Other neat tricks could be applied if you do so wish, I found the following to be quite helpful in getting ideas:

Animation Overview (MSDN)

Storyboards Overview (MSDN)