MVVM and Animations in Silverlight

March 30, 2012 · 1 min read

I wanted to spin an icon to show progress to my user while some content was downloading. I'm using MVVM (aren't you) and made a satisfactory Storyboard to spin the icon. However, it took longer than expected to trigger that animation from my ViewModel's property.

I used a combination of the GoToState action and the DataTrigger from the Microsoft.Expression.Interactions dll as described.

Then I had problems getting it to start until I found this approach that saved the day. The DataTrigger didn't bind right away because "it doesn’t change visual state on load is because the StateTarget property of the GotoStateAction is null at the time the DataTrigger fires."

Here's my XAML, hopefully you can fill in the rest.

<Image x:Name="StatusIcon" AutomationProperties.AutomationId="StatusIcon" Width="16" Height="16" Stretch="Fill"

Source="inProgress.png" ToolTipService.ToolTip="{Binding StatusTooltip}">

<i:Interaction.Triggers>

<utilitiesBehaviors:DataTriggerWhichFiresOnLoad Value="True" Binding="{Binding IsDownloading, Mode=OneWay, TargetNullValue=True}">

<ei:GoToStateAction StateName="Downloading" />

</utilitiesBehaviors:DataTriggerWhichFiresOnLoad>

<utilitiesBehaviors:DataTriggerWhichFiresOnLoad Value="False" Binding="{Binding IsDownloading, Mode=OneWay, TargetNullValue=True}">

<ei:GoToStateAction StateName="Complete"/>

</utilitiesBehaviors:DataTriggerWhichFiresOnLoad>

</i:Interaction.Triggers>

<Image.Projection>

</Image.Projection>

<VisualStateManager.VisualStateGroups>

<VisualStateGroup.Transitions>

<VisualTransition.GeneratedEasingFunction>

</VisualTransition.GeneratedEasingFunction>

</VisualStateGroup.Transitions>

</VisualStateManager.VisualStateGroups>

MVVMAnimations.zip

This article is part of the GWB Archives. Original Author: Aligned

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