Achieve “slide down” animation in WPF

Question

I am attempting to create my own template for an Expander control. When the control is expanded, I want the content to slide down slowly.

The desired he

Answer 1

If you can use Interactions with FluidLayout (Blend 4 SDK) you are in luck, it's really useful for those fancy animation things.

First set the content CP's Height to 0:

To animate this, the Height just needs to be animated to NaN in the VisualState that represents the expanded state (non-discrete animations would not let you use NaN):

xmlns:is="http://schemas.microsoft.com/expression/2010/interactions"

That should be all that is necessary, the fluid layout will create the transition for you from there.

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If you have a code-behind solution that would be fine, you can even use code-behind in dictionaries like this:

//TestDictionary.xaml.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;

namespace Test
{
    partial class TestDictionary : ResourceDictionary
    {
        //Handlers and such here
    }
}