如何为依赖项属性创建公共事件？

Question

在下面的代码中,您可以看到我正在尝试做什么,但它不起作用.我想要一个事件,我可以附加到我的用户控件之外,并在依赖项属性更改时触发.

    public static readonly DependencyProperty ValueProperty =
        DependencyProperty.Register("Value"
        , typeof(Double)
        , typeof(ucSlider)
        , new PropertyMetadata(50d, new PropertyChangedCallback(OnValueChanged)));

    public Double Value
    {
        get { return (Double)GetValue(ValueProperty); }
        set { SetValue(ValueProperty, value); }
    }

    public event PropertyChangedCallback OnValueChanged;

Answer 1

依赖项属性是静态的,但您的事件与类的实例相关.因此,您需要静态属性和实例事件之间的中间方法.

在这个例子中,我将静态方法OnValuePropertyChanged作为回调参数传递,并在其中引发事件:

public static readonly DependencyProperty ValueProperty =
    DependencyProperty.Register("Value"
    , typeof(Double)
    , typeof(ucSlider)
    , new PropertyMetadata(50d, new PropertyChangedCallback(OnValuePropertyChanged)));

public Double Value
{
    get { return (Double)GetValue(ValueProperty); }
    set { SetValue(ValueProperty, value); }
}

public static void OnValuePropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
    var sl = sender as ucSlider;
    if (sl != null)
        sl.RaiseValueChangedEvent(e);
}

private void RaiseValueChangedEvent(DependencyPropertyChangedEventArgs e)
{
    if(this.OnValueChanged != null)
        this.OnValueChanged(this, e);
}

public event PropertyChangedCallback OnValueChanged;