Animation a Silverlight UI element width from 0 to auto, smoothly

I have a Silverlight UI with a slide-out panel. When a button is clicked, I’d like the panel to animate out smoothly, with the width going from 0 to Auto. Is there a way to do this (ideally with pure XAML)?

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3 Answer(s)

why dont you just animate the maxwidth? Dont think you’ll be able to animate to auto

Answered on July 11, 2016.
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WOW that really made me think 🙂 but I believe that I found a workaround that you can use. You will need a Converter but it’s the only code you need in C# – the rest is in pure XAML.

I have reconstructed some XAML based on your input:

            TranslateX="{Binding ActualWidth, Converter={StaticResource InverseTranslateXConverter}, ElementName=m_Grid}" />
        Content="Hello World" />

So what I do is actually is just to wrap the slider inside a grid and set the TranslateX property to the ActualWidth of the content * -1 (done using a converter):

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    double d = 0;
    if (double.TryParse(value.ToString(), out d))
        return d * -1;

    return value;

To show it (slide in) I use a simple animation:

        d:IsOptimized="True" />

It’s not pretty but it works 🙂

[EDIT] Just removed the outergrid – it was unnessesary.

Answered on July 11, 2016.
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It is not possible to animate Auto values, but as a workaround you can use VisualStateManager and FluidLayout with the following steps:
– Add a state group in Expression Blend
– Add the initial state
– Add the final state
– Change the visisbility to Collapsed in Blend
– Enable FluidLayout
– Write code to switch between states
– This will animate both width, height, and opacity of the element while showing it using a custom VisualStateManager
– You can write your own custom state manager to control the transition between discrete states

Answered on July 11, 2016.
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