即时依赖属性

Question

我有一个类，它可以实时计算属性，例如：

class CircleArea
{
    public double Radius { get; set; }
    public double Area
    {
        get
        {
            return Radius * Radius * Math.PI;
        }
    }
}

我将其转换为DependencyObject，方法如下：

我这么做:

class CircleArea:
    DependencyObject
{
    public static readonly DependencyProperty RadiusProperty =
        DependencyProperty.Register("Radius", typeof(double), typeof(CircleArea));
    public double Radius
    {
        get { return (double)GetValue(RadiusProperty); }
        set
        {
            SetValue(RadiusProperty, value);
            CoerceValue(AreaProperty);
        }
    }

    internal static readonly DependencyPropertyKey AreaPropertyKey =
        DependencyProperty.RegisterReadOnly("Area", typeof(double), typeof(CircleArea), new PropertyMetadata(double.NaN));
    public static readonly DependencyProperty AreaProperty = AreaPropertyKey.DependencyProperty;
    public double Area
    {
        get
        {
            return Radius * Radius * Math.PI;
        }
    }
}

我在XAML中有两个文本框，一个使用双向绑定到半径，另一个使用单向绑定到面积。

我该怎么做才能使对半径文本框的编辑更新面积文本框？

- 曾其威

---

我尝试了 CoerceValue(AreaProperty); 和 InvalidateProperty(AreaProperty);，但它们都没有起作用。 - Palatis

Answer 1

您可以通过以下几种方式进行操作。

• For simplicity, you can implement INotifyPropertyChanged, use a regular property for Area, and then trigger the event in the OnDependencyPropertyChanged for RadiusProperty.

• For more complexity, you'd set AreaProperty using the key privately whenever Radius changes. Your property would look like this.

  public static readonly DependencyProperty RadiusProperty = 
      DependencyProperty.Register(
          "Radius",  
          typeof(double), 
          typeof(CircleArea), 
          new FrameworkPropertyMetadata(0.0, OnRadiusChanged))
  
  
  private static void OnRadiusChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
       Area = Radius * Radius * Math.PI;
  }
  
  
  
  private static readonly DependencyPropertyKey AreaKey=
      DependencyProperty.RegisterReadOnly("Area", typeof(double)...
  public static readonly DependencyProperty AreaProperty = AreaKey.DependencyProperty;
  
  public Double Area
  {
      get
      {
          return (Double)GetValue(AreaProperty);
      }
      private set
      {
          SetValue(AreaKey, value);
      }
  }
  

您仍然可以将单向绑定设置为 Area。

- Lee Louviere