依赖属性重新入侵(或者:为什么这有效？)

Question

简而言之,我可以在WPF控件中创建2个依赖项属性,并将代码放在每个属性更改通知中以更改其他属性(即PropA更改集PropB和PropB更改集PropA).

我希望这会消失在自己的背后,但WPF似乎很好地处理它.这对我的目的来说实际上非常方便,但我无法在任何地方找到这种行为.

发生什么了？WPF依赖项属性是否会更改通知系统防止重入？

代表性代码如下:

XAML:

<Window x:Class="WPFReentrancy1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TextBox Text="{Binding PropB, UpdateSourceTrigger=PropertyChanged}"/>

    </Grid>
</Window>

代码背后:

 public partial class MainWindow : Window
    {

        public string PropA
        {
            get { return (string)GetValue(PropAProperty); }
            set { SetValue(PropAProperty, value); }
        }
        public static readonly DependencyProperty PropAProperty =
                        DependencyProperty.Register("PropA", typeof (string), typeof (MainWindow),new UIPropertyMetadata("0", PropAChanged));


        public string PropB
        {
            get { return (string)GetValue(PropBProperty); }
            set { SetValue(PropBProperty, value); }
        }

        public static readonly DependencyProperty PropBProperty =
            DependencyProperty.Register("PropB", typeof (string), typeof (MainWindow), new UIPropertyMetadata("", PropBChanged));

        private static void PropBChanged(DependencyObject lDependencyObject, DependencyPropertyChangedEventArgs lDependencyPropertyChangedEventArgs)
        {
            ((MainWindow) lDependencyObject).PropA = (string) lDependencyPropertyChangedEventArgs.NewValue;
        }


        private static void PropAChanged(DependencyObject lDependencyObject, DependencyPropertyChangedEventArgs lDependencyPropertyChangedEventArgs)
        {
            ((MainWindow) lDependencyObject).PropB =
                double.Parse((string) lDependencyPropertyChangedEventArgs.NewValue).ToString("0.000");
        }


        public MainWindow()
        {
            InitializeComponent();
            DataContext = this;
            PropA = "1.123";
        }
    }

Answer 1

这些回调仅在属性更改时才会触发，您的代码不会创建不同值的无限循环。

试试这个，你会得到一个异常：

private static readonly Random _random = new Random();
private static void PropBChanged(DependencyObject lDependencyObject, DependencyPropertyChangedEventArgs lDependencyPropertyChangedEventArgs)
{
    ((MainWindow)lDependencyObject).PropA = _random.Next().ToString();
}
private static void PropAChanged(DependencyObject lDependencyObject, DependencyPropertyChangedEventArgs lDependencyPropertyChangedEventArgs)
{
    ((MainWindow)lDependencyObject).PropB = _random.Next().ToString();
}