On-The-Fly DependencyProperties

本文关键字：DependencyProperties On-The-Fly | 更新日期: 2023-09-27 18:06:44

我有一个类可以即时计算它的属性，例如:

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

我使它成为一个DependencyObject:

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;
        }
    }
}

然后我在XAML中有两个文本框，一个是单向绑定到Radius，另一个是单向绑定到Area。

我应该做些什么来编辑半径的文本框更新区域的文本框?

On-The-Fly DependencyProperties

有几种方法可以做到这一点。

为简单起见，您可以实现INotifyPropertyChanged，为Area使用常规属性，然后为RadiusProperty触发OnDependencyPropertyChanged中的事件。

为了更复杂，您将在Radius更改时使用私钥设置AreaProperty。您的属性看起来像这样。

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);
    }
}

你仍然可以设置一个单向绑定到Area。