How can I control the SpeedRatio of a Storyboard inside a VisualState?

Given a Storyboard started by the VisualStateManager as part of a ControlTemplate, how would I adjust the SpeedRatio of that animation based on property changes of the control?

<ControlTemplate>
  <Grid>
    <VisualStateManager.Visu开发者_C百科alStateGroups>
      <VisualStateGroup>
        <VisualState>
          <Storyboard Name="SpinningThing"
                      SpeedRatio="{Binding SpinningSpeedRatio}">
            ...

This needs to work in both WPF and Silverlight.

I don't think I can set a binding there for a number of reasons. Foremost, Storyboard is Freezable so you can't just go setting the SpeedRatio all willy-nilly in WPF. But, if it's started by the VisualStateManager, can I call SetSpeedRatio on it?

Also, since its parent is a VisualState, doesn't that mean there would be no governing FrameworkElement to relate to for it?

So, if I can't do it with a binding, how can this be done?

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For those arriving here looking for a UWP solution, you can use an {x:Bind} on the SpeedRatio property of a Storyboard and it does dynamically change the speed ratio as you would expect.

<Storyboard SpeedRatio="{x:Bind ViewModel.SpinningSpeedRatio, Mode=OneWay}">

Edit: One caveat is you need to ensure you set the ratio on the UIThread, otherwise it will be ignored by the VisualStateManager. The Storyboard will still play, but not at the speed you have set.

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Normally you would use a {TemplateBinding...} rather than a {Binding...}, but that only works for simple, compatible, types.

You should also be able to bind to the templated control using a "relative binding source". This also allows you to use a value convertor if the types do not match.

SpeedRation={Binding SomeProperty, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource SomeConverter}}" 

I have not tested this in WPF, but Silverlight is normally the feature-restricted one.

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Alright, so it looks like there really is no way to handle this strictly with a binding. So to account for it, I have hooked events in the code-behind to start/adjust the animations as appropriate.