Silverlight 依赖属性更改事件问题

Question

我有一个具有依赖属性的自定义控件...它有几个，但让我们说可拖动是我的问题。该属性是一个 bool 值，每次更改时我都想执行一段代码...一个切换。

我有两个选项，都显示在下面

[Category("Modal Options")]
    public bool Dragable
    {
        get { return (bool)GetValue(DragableProperty); }
        set { SetValue(DragableProperty, value); toggleDragable(); }
    }

    // Using a DependencyProperty as the backing store for Dragable.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty DragableProperty =
        DependencyProperty.Register("Dragable", typeof(bool), 
        typeof(PlussWindow), new PropertyMetadata(false));

    private void MakeDragable()
    {
        this.dragBehavior.Attach(this.LayoutRoot);
    }

    private void MakeUnDragable()
    {
        this.dragBehavior.Detach();
    }

    public virtual void toggleDragable()
    {
        if (this.Dragable)
        {
            MakeUnDragable();
        }
        else
        {
            MakeDragable();
        }
    }

或

[Category("Modal Options")]
    public bool Dragable
    {
        get { return (bool)GetValue(DragableProperty); }
        set { SetValue(DragableProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Dragable.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty DragableProperty =
        DependencyProperty.Register("Dragable", typeof(bool), 
        typeof(PlussWindow), new PropertyMetadata(false, (o, e) => { (o as PlussWindow).toggleDragable(); } 
         ));

    private void MakeDragable()
    {
        this.dragBehavior.Attach(this.LayoutRoot);
    }

    private void MakeUnDragable()
    {
        this.dragBehavior.Detach();
    }

    public virtual void toggleDragable()
    {
        if (this.Dragable)
        {
            MakeUnDragable();
        }
        else
        {
            MakeDragable();
        }
    }

每个方法都会导致“对象引用未设置为对象的实例”

我通常使用绑定(bind)来解决这个问题，例如，可见性或文本很容易完成，但对于自定义功能，我需要在代码中启用它。

我该怎么做，注意到 propertychanged 方法是静态的？

Answer 1

试试这个:

public bool Dragable
    {
        get { return (bool)GetValue(DragableProperty); }
        set { SetValue(DragableProperty, value); }
    }

    public static readonly DependencyProperty DragableProperty =
        DependencyProperty.Register("Dragable", typeof(bool), typeof(PlussWindow), new PropertyMetadata(false, new PropertyChangedCallback(onDragableChange)));

    private static void onDragableChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        bool validate = (bool)e.NewValue;
        PlussWindow win = (PlussWindow) d;

        if (validate)
        {
            win.dragBehavior.Attach(this.LayoutRoot);
        }

        else
        {
            win.dragBehavior.Detach();
        }


    }