Question

I’m trying to set up a dependency property which is of an object called a Sprite, a sprite contains a string of a spriteSheet, so i want to be able to pass a Sprite and then that data is used to display an image in my control.

This is my attempt as it stands

    public Sprite Sprite
    {
        get { return (Quiz.Sprite)GetValue(SpriteProperty); }
        set {
            spriteBrush.ImageSource = new BitmapImage(new Uri("/Project;component/" + value.spriteSheet, UriKind.RelativeOrAbsolute));

            spriteTransform.TranslateX = -558;
            spriteTransform.TranslateY = 0;

            SetValue(SpriteProperty, value);
        }
    }

    public static DependencyProperty SpriteProperty = DependencyProperty.Register(
       "Sprite", typeof(Sprite), typeof(spriteView), new PropertyMetadata(new Quiz.Sprite() { spriteSheet = "wp7_buttons.png" }));
}

How do I get that portion of the set method to run, as i’ve read in the Dependency Property docs that SetValue and GetValue might get called directly when binding.

Answer 1

That’s correct, you cannot use SetValue to introduce any logic. Instead, you should use a PropertyValueChanged handler. Something like:

public Sprite Sprite
{
    get { return (Quiz.Sprite)GetValue(SpriteProperty); }
    set { SetValue(SpriteProperty, value); }
}

private static void OnSpritPropertyValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
    var control = d as YourControl;
    var sprite = e.NewValue as Quiz.Sprite;

    control.spriteBrush.ImageSource = new BitmapImage(new Uri("/Project;component/" + sprite.spriteSheet, UriKind.RelativeOrAbsolute));

    control.spriteTransform.TranslateX = -558;
    control.spriteTransform.TranslateY = 0;
}

public static DependencyProperty SpriteProperty = DependencyProperty.Register(
   "Sprite", typeof(Sprite), typeof(spriteView),
    new PropertyMetadata(new Quiz.Sprite() { spriteSheet = "wp7_buttons.png" }, OnSpritPropertyValueChanged));