C# WPF依赖属性回调

我有一个具有依赖属性的用户控件，我正在wpf窗口中使用此控件。当我从窗口视图模型更改作为该依赖项属性绑定的属性的值时，我希望调用该依赖项属性的回调方法，但什么也没有发生

MainWindow.xaml

 <test:TestView Grid.Column="0" TestString="{Binding TestString, Mode=TwoWay}"></test:TestView>

MainWindowViewModel.cs

 private string _testString;

    public string TestString
    {
        get { return _testString; }
        set
        {
            if (_testString!= value)
            {
                _testString= value;
                OnPropertyChanged();
            }
        }
    }

TestView.xaml.cs

public TestView()
    {
        InitializeComponent();
        this.DataContext = new TestViewModel();
    }

    public static readonly DependencyProperty TestStringProperty =
        DependencyProperty.Register("TestString", typeof(string), typeof(TestView), new PropertyMetadata(null, OnTestStringPropertyChanged));
    public string TestString
    {
        get { return (string)GetValue(TestStringProperty); }
        set
        {
            SetValue(TestStringProperty, value);
        }
    }

    private static void OnTestStringPropertyChanged(DependencyObject source,
    DependencyPropertyChangedEventArgs e)
    {
        TestView control = source as TestView;
        string time = (string)e.NewValue;
        // Put some update logic here...
        ((TestViewModel) control.DataContext).Merge();
    }

BaseViewModel.cs（我在每个ViewModel中扩展它）

---

我在这里做错了什么，或者为什么我的回调从未被调用？

我们可以看看您是如何实现的

INotifyPropertyChanged

？删除

this.DataContext=new TestViewModel（）。它会中断任何基于DataContext的绑定，如
TestString=“{Binding TestString，Mode=TwoWay}”
。UserControl永远不应该显式设置自己的DataContext。@scharette我编辑了这个问题，现在您也可以看到实现，如果INotifyPropertyChangedAs说，UserControl永远不应该显式设置自己的DataContext。既不是对自身，也不是对某些“私有”视图模型。它应该只公开绑定到外部提供的视图模型属性的依赖属性，即UserControl父元素的DataContext属性的值继承提供的依赖属性，例如MainWindow。这正是您应该做的。
public TestView()
    {
        InitializeComponent();
        this.DataContext = new TestViewModel();
    }

    public static readonly DependencyProperty TestStringProperty =
        DependencyProperty.Register("TestString", typeof(string), typeof(TestView), new PropertyMetadata(null, OnTestStringPropertyChanged));
    public string TestString
    {
        get { return (string)GetValue(TestStringProperty); }
        set
        {
            SetValue(TestStringProperty, value);
        }
    }

    private static void OnTestStringPropertyChanged(DependencyObject source,
    DependencyPropertyChangedEventArgs e)
    {
        TestView control = source as TestView;
        string time = (string)e.NewValue;
        // Put some update logic here...
        ((TestViewModel) control.DataContext).Merge();
    }

public class BaseViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}