在本地窗口资源中使用时，为什么绑定到属性不起作用？

Question

I have a storyboard with an animation in MainWindow.xaml Window.Resources section:

<Window.Resources>
    <Storyboard x:Key="ShowSearchGrid">
        <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(FrameworkElement.Height)" Storyboard.TargetName="SearchGrid">
            <EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="{Binding ExpandedGridHeight}"/>
        </DoubleAnimationUsingKeyFrames>
    </Storyboard>
</Window.Resources>

The property ExpandedGridHeight is defined in a custom class like so:

class ExpandedGridHeightClass : INotifyPropertyChanged
{
    //The next bit handles the INotifyPropertyChanged implementation

    public event PropertyChangedEventHandler PropertyChanged;

    protected void Notify(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public Double ExpandedGridHeight
    {
        get { return _expandedGridHeight; }
        set
        {
            if (value != _expandedGridHeight)
            {
                _expandedGridHeight = value;
                Notify("ExpandedGridHeight");
            }
        }
    }

    private Double _expandedGridHeight = 100;
}

The data context for the window is set in MainWindow():

ExpandedGridHeightClass ExpandedHeight;

public MainWindow()
{
    InitializeComponent();

    ExpandedHeight = new ExpandedGridHeightClass();
    this.DataContext = ExpandedHeight;
}

The actual value for ExpandedHeight's ExpandedGridHeight property is set elsewhere, and changes depending on the size of the window.

The storyboard is started from the following function:

void showSearchGrid()
{
    Storyboard ShowSearchGrid = this.FindResource("ShowSearchGrid") as Storyboard;
    ShowSearchGrid.Begin();
}

When I tried to bind the property to various other places like to the title of the window, it worked perfectly, and updated exactly as intended. However, when it is binded like in the code examples to a property in the local resources, it doesn't work: the animation does start as usual, but instead of animating to ExpandedGridHeight, the SearchGrid is animated to a height value of 0. I'm suspecting it is because the animation is defined in the resources, but don't know a fix to this problem. Any help would be appreciated! :)

Answer 1

Just thought I might as well put this as an answer. This method is definitely "hackish", so it may not be to your liking.

ExpandedGridHeightClass:

class ExpandedGridHeightClass : INotifyPropertyChanged
{
    private static ExpandedGridHeightClass _instance;
    public static ExpandedGridHeightClass Instance
    {
        get
        {
            if (_instance == null)
                _instance = new ExpandedGridHeightClass();
            return _instance;
        }
    }

    /**
     * Whatever your class already has
     */
}

XAML:

<EasingDoubleKeyFrame KeyTime="0:0:0.5"
    Value="{Binding ExpandedGridHeight, Source={x:Static MyNamespace:ExpandedGridHeightClass.Instance}}"/>