WPF 双向绑定到属性的属性以替换父属性

Question

我有一个使用 DependencyProperties（或 INotifyPropertyChanged）的 ViewModel，它有一个非常简单的复合类型属性，例如 System.Windows.Point。 简单复合类型不使用 DependencyProperties 或 INotifyPropertyChanged，它打算保持这种状态（这是我无法控制的）。

我现在想做的是创建双向数据绑定到 Point 的 X 和 Y 属性，但是当其中之一发生更改时，我想要替换整个 Point class ，而不是只更新成员。

代码示例仅供说明：

<Window ...>
    <StackPanel>
        <TextBox Text="{Binding TestPoint.X, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, StringFormat=\{0:F\}}"/>
        <TextBox Text="{Binding TestPoint.Y, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, StringFormat=\{0:F\}}"/>
        <!-- make following label update based on textbox changes above -->
        <Label Content="{Binding TestPoint, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}}"/>
    </StackPanel>
</Window>

代码隐藏：

public partial class MainWindow : Window
{
    public Point TestPoint
    {
        get { return (Point)GetValue(TestPointProperty); }
        set { SetValue(TestPointProperty, value); }
    }
    public static readonly DependencyProperty TestPointProperty = DependencyProperty.Register("TestPoint", typeof(Point), typeof(MainWindow), new PropertyMetadata(new Point(1.0, 1.0)));
}

我的想法是将两个TextBox直接绑定到TestPoint 属性并使用IValueConverter仅过滤掉特定成员，但是ConvertBack方法出现问题，因为Y值不再存在修改X值时。

我觉得一定有一个我没有得到的非常简单的解决方案。

编辑：

上面的代码只是一个简化的例子，实际的应用要复杂得多。复合类型有大约 7 个成员，并且在整个应用程序中普遍使用，因此将它拆分为单个成员感觉不对。另外我想依靠依赖项属性的 OnChanged 事件来调用其他更新，所以我真的需要替换整个 class.

Answer 1

我认为在这种情况下，引入两个 DependencyProperties，一个用于 X 值，一个用于 Y 值并简单地绑定到它们会更容易。在每个 DependencyProperty 的 PropertyMetadata 中注册一个方法，s.th。在每次值更改时，如果您仍然需要，您可以替换您的 Point 对象。

您还可以使用适当的单向 IMultiValueConverter 将您的标签绑定到两个属性的 MultiBinding。

Answer 2

你为什么不使用访问器？

public partial class MainWindow : Window
{
    public Point TestPoint
    {
        get { return (Point)GetValue(TestPointProperty); }
        set { SetValue(TestPointProperty, value); }
    }

    public double TestPointX
    {
        get { return this.TestPoint.X; }
        set
        { 
            SetValue(TestPointProperty, new Point(value, this.TestPointY);
        }
    }

    public double TestPointY
    {
        get { return this.TestPoint.Y; }
        set
        { 
            SetValue(TestPointProperty, new Point(this.TestPointX, value);
        }
    }

    public static readonly DependencyProperty TestPointProperty = DependencyProperty.Register("TestPoint", typeof(Point), typeof(MainWindow), new PropertyMetadata(new Point(1.0, 1.0)));
}

在你的 XAML 中：

<Window ...>
<StackPanel>
        <TextBox Text="{Binding TestPointX, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, StringFormat=\{0:F\}}"/>
        <TextBox Text="{Binding TestPointY, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, StringFormat=\{0:F\}}"/>
        <Label Content="{Binding TestPoint, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}}"/>
    </StackPanel>
</Window>

Answer 3

正如我在评论中所说，您可以这样尝试。当我们将转换器添加到特定控件的资源时，相同的实例将用于子控件。

  <Grid>
    <Grid.Resources />
    <StackPanel>
        <StackPanel>
            <StackPanel.Resources>
                <local:PointConverter x:Key="PointConverter" />
            </StackPanel.Resources>
            <TextBox Text="{Binding TestPoint, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Converter={StaticResource PointConverter}, ConverterParameter=x}" />
            <TextBox Text="{Binding TestPoint, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Converter={StaticResource PointConverter}, ConverterParameter=y}" />
            <!--  make following label update based on textbox changes above  -->
            <Label Content="{Binding TestPoint, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}}" />
        </StackPanel>
        <StackPanel>
            <StackPanel.Resources>
                <local:PointConverter x:Key="PointConverter" />
            </StackPanel.Resources>
            <TextBox Text="{Binding TestPoint2, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Converter={StaticResource PointConverter}, ConverterParameter=x}" />
            <TextBox Text="{Binding TestPoint2, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}, Converter={StaticResource PointConverter}, ConverterParameter=y}" />
            <!--  make following label update based on textbox changes above  -->
            <Label Content="{Binding TestPoint2, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainWindow}}}" />
        </StackPanel>
    </StackPanel>
</Grid>

和后面的代码，

    public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }


    public Point TestPoint
    {
        get
        {
            return (Point)GetValue(TestPointProperty);
        }
        set
        {
            SetValue(TestPointProperty, value);
        }
    }

    // Using a DependencyProperty as the backing store for TestPoint.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TestPointProperty =
        DependencyProperty.Register("TestPoint", typeof(Point), typeof(MainWindow), new PropertyMetadata(new Point(1.0, 1.0)));
     public Point TestPoint2
    {
        get
        {
            return (Point)GetValue(TestPoint2Property);
        }
        set
        {
            SetValue(TestPoint2Property, value);
        }
    }

    // Using a DependencyProperty as the backing store for TestPoint.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TestPoint2Property =
        DependencyProperty.Register("TestPoint2", typeof(Point), typeof(MainWindow), new PropertyMetadata(new Point(1.0, 1.0)));


}

public class PointConverter : IValueConverter
{
    double knownX = 0.0;
    double knownY = 0.0;
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
         if (parameter.ToString() == "x")
        {
            knownX = ((Point)value).X;
            return ((Point)value).X;
        }
        else
        {
            knownY = ((Point)value).Y;
            return ((Point)value).Y;
        }

    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {

         Point p = new Point();
        if (parameter.ToString() == "x")
        {
            p.Y = knownY;
            p.X = double.Parse(value.ToString());
        }
        else
        {
            p.X = knownX;
            p.Y = double.Parse(value.ToString());
        }
        return p;
    }
}

注意：我没有添加任何空检查。

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