WPF-将参数从对话框窗口传递到UserControl

Question

I'm using DependencyProperty to pass parameters from DialogWindow to UserControl. I want that parameter inside the UserControl constructor in order to pass it to the view model.

The property always returns null, and never get set.

Code:

MainWindow:

var dialog = new DialogWindow();
dialog.ShowDialog();

DialogWindow.xaml

<TabControl>
    <TabItem Header="Data Source">
        <local:DataSourceView Test="Something" />
    </TabItem>
</TabControl>

DataSourceView.xaml.cs

public static readonly DependencyProperty TestProperty =
    DependencyProperty.Register("Test", typeof(object), typeof(DataSourceView));
public object Test {
    get { return (object)GetValue(TestProperty); }
    set { SetValue(TestProperty, value); }
}
public DataSourceView() {
    InitializeComponent();
    DataContext = new DataSourceViewModel(Test);// Test is always null
}

Answer 1

You can use overload of DependencyProperty.Register method with PropertyMetadata which will have a PropertyChangedCallback parameter and observe data binding process.

    public static readonly DependencyProperty TestProperty =
      DependencyProperty.Register("Test", typeof(object), typeof(DataSourceView), new PropertyMetadata(TestPropertyChangedCallback
    ));

    private static void TestPropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine(e.NewValue);
        System.Diagnostics.Debug.WriteLine(e.OldValue);
    }

Following link contains the solution for a similar problem:

Passing Parameters between xaml window and usercontrol WPF

Answer 2

"The property always returns null, and never get set." - Is wrong. The property is null in DataSourceView constructor. After the instance of DataSourceView is created, property will be set to "Something".