CODEWITHSUNDEEP
wpfdependency-properties
JanSkalicky
JanSkalicky

Reputation: 1007

WPF: instances of usercontrol share dependency properties

I made an usercontrol and it works great, but when I put two instances of this control to one window, only the last of them works. I tried to find solution and I realized, that dependency properties are shared, but I dont know how to get it work.

Here is my dependency property:

    public double AnimatingVerticalOffset
    {
        get { return (double)GetValue(AnimatingVerticalOffsetProperty); }
        set { SetValue(AnimatingVerticalOffsetProperty, value); }
    }

    public static readonly DependencyProperty AnimatingVerticalOffsetProperty;

    static ListChooser()
    {
        ListChooser.AnimatingVerticalOffsetProperty =
                   DependencyProperty.Register("AnimatingVerticalOffset", typeof(double), typeof(ListChooser), new UIPropertyMetadata(OnAnimationVerticalOffsetChanged));
    }

Upvotes: 3

Views: 2474

Answers (1)

Matěj Zábský
Matěj Zábský

Reputation: 17272

The dependency property itself must be static with no ties to one single instance. And that applies for its callbacks too (OnAnimationVerticalOffsetChanged in your case) - these must be static methods (don't worry, the object instance is passed via its parameter, you just have to do some type casting to ensure the object is the type you are working with).

You should use static initializer to initialize DP, the method you used (initializing in constructor) works, but the DP will overwrite for each instance.

See this question for deeper explanation.

EDIT:

Corrected code:

public double AnimatingVerticalOffset
{
    get { return (double)GetValue(AnimatingVerticalOffsetProperty); }
    set { SetValue(AnimatingVerticalOffsetProperty, value); }
}

public static readonly DependencyProperty AnimatingVerticalOffsetProperty =
               DependencyProperty.Register("AnimatingVerticalOffset", typeof(double), typeof(ListChooser), new UIPropertyMetadata(OnAnimationVerticalOffsetChanged));

static ListChooser()
{
}

If the callback is not static, you will get compile error (=> you have to make it static).

EDIT:

Remember, the DP definition is static, not the property's value itself! DPs work exactly just like any other property, it just has some extra features: value inhertiance, bidnings, animation...

Upvotes: 2

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