Define VisualStates from Codebehind

Question

is it possible to define (not switch) VisualStates in CodeBehind?

I'm creating an Adorner, that draws some rectangles in OnRender. What I'd like to do is to change the Opacity of these Rectangles by it's Property IsMouseOver (say from 0.3 to 0.8).

In any control with a visual tree I'd add some VisualStates and switch those with a DataStateBehavior. How do I do this with an Adorner?

Answer 1

this is entirely possible.

if anyone is interested here is how I did it:

public class MyAdorner: Adorner
{
    ctor (...):base(...)
    {
        ...

        var storyboard = new Storyboard();
        var doubleAnimation = new DoubleAnimation(0.2,new Duration(TimeSpan.Zero));
        Storyboard.SetTarget(doubleAnimation,this);
        Storyboard.SetTargetProperty(doubleAnimation,new PropertyPath(RectOpacityProperty));
        storyboard.Children.Add(doubleAnimation);

        var storyboard2 = new Storyboard();
        var doubleAnimation2 = new DoubleAnimation(0.5, new Duration(TimeSpan.Zero));
        Storyboard.SetTarget(doubleAnimation2, this);
        Storyboard.SetTargetProperty(doubleAnimation2, new PropertyPath(RectOpacityProperty));
        storyboard2.Children.Add(doubleAnimation2);

        var stateGroup = new VisualStateGroup { Name = "MouseOverState" };
        stateGroup.States.Add(new VisualState { Name = "MouseOut", Storyboard = storyboard });
        stateGroup.States.Add(new VisualState { Name = "MouseOver", Storyboard = storyboard2});

        var sgs = VisualStateManager.GetVisualStateGroups(this);
        sgs.Add(stateGroup);

        var dsb = new DataStateBehavior
            {
                Value = true,
                FalseState = "MouseOut",
                TrueState = "MouseOver"
            };
        BindingOperations.SetBinding(dsb, DataStateBehavior.BindingProperty, new Binding {Source = this, Path = new PropertyPath(IsMouseOverProperty)});
        dsb.Attach(this);

    }

    protected override void OnRender(DrawingContext drawingContext)
    {
        drawingContext.DrawRectangle(_mouseOverBrush, _pen, _rects[i]);     //mouseoverbrush is a Solidcolorbrush       
    }

    public double RectOpacity
    {
        get { return (double)GetValue(RectOpacityProperty); }
        set { SetValue(RectOpacityProperty, value); }
    }

    public static readonly DependencyProperty RectOpacityProperty =
        DependencyProperty.Register("RectOpacity", typeof(double), typeof(XmlNodeWrapperAdorner), new FrameworkPropertyMetadata(0.0,FrameworkPropertyMetadataOptions.AffectsRender,(o, args) =>
            {
                var adorner = o as MyAdorner;
                adorner._mouseOverBrush.Color = Color.FromArgb((byte)((double)args.NewValue * 0xFF), 0xFF, 0xBE, 0x00);
            }));

}

pretty straightforward actually.

key points here are:

• you cannot set the VisualStateGroups attached property. you have to get the collection and then add your own group

• you cannot do new DataStateBehavior{Binding = new Binding(...){...}} as this will assign not bind some value to the property. As Behvior<T> doesn't derive from FrameworkElement you also can't use SetBinding but have to use the BindingOperations class.

• for automatic rerendering when the property changes keep in mind to set FrameworkPropertyMetadataOptions.AffectsRender.