wpf - 绑定(bind) WPF UserControl 以查看模型和代码

Question

我试图了解连接自定义控件以使用依赖属性和 View 模型的最佳方式。实现依赖属性以公开可在 XAML 中用于初始化 View 模型中的属性的属性。例如，在自定义控件的代码中，我可以定义以下依赖属性:

public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register(
         "MyProperty", typeof(string), typeof(MyControl), new PropertyMetadata(null));

public string MyProperty
{
  get { return (string)GetValue(MyPropertyProperty); }
  set { SetValue(MyPropertyProperty, value); }
}

View 模型定义为

public class MyControlViewModel : INotifyPropertyChanged
   {
      public MyControlViewModel()
      {
         _myProperty = "Default View Model string";
      }

      private string _myProperty;

      public string MyProperty
      {
         get
         {
            return _myProperty;
         }
         set
         {
            _myProperty = value;
            OnPropertyChanged("MyProperty");
         }
      }

      public event PropertyChangedEventHandler PropertyChanged;

      protected virtual void OnPropertyChanged(string propertyName = null)
      {
         var handler = PropertyChanged;
         if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));

      }
   }

并且自定义控件绑定(bind)到 View Model MyProperty 如下

<UserControl x:Class="MyProject.MyControlView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:MyProject">

    <UserControl.DataContext>
        <local:MyControlViewModel/>
    </UserControl.DataContext>

    <Grid>
        <TextBlock Text="{Binding MyProperty}"/>                
    </Grid>

</UserControl>

现在，由于我在自定义控件的代码中定义了依赖属性 MyProperty，我希望能够使用它来初始化 ViewModel 中的 MyProperty。所以像这样

 <Window x:Class="MyProject.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyProject"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <local:MyControlView MyProperty="This was set in XAML"/>
    </Grid>
</Window>

运行上述将显示在 View 模型的构造函数中设置的字符串“默认 View 模型字符串”。如何连接依赖属性值，以便正确初始化 View 模型中的字符串？即它应该显示“这是在 XAML 中设置的”。

更新

我可以在后面的代码中设置属性更改回调并在 View 模型中设置值，即

public static readonly DependencyProperty MyPropertyProperty =
          DependencyProperty.Register("MyProperty", typeof(string), typeof(MyControlView), new PropertyMetadata("Default", OnMyPropertyChanged));

      private static void OnMyPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
      {
         var view = d as MyControlView;
         if (view != null)
         {
            var viewModel = view.DataContext as MyControlViewModel;
            if (viewModel != null)
            {
               viewModel.MyProperty = e.NewValue as string;
            }
         }
      }

这是正确的，还是有气味？

Answer 1

您已经创建了很好的依赖属性。但是，您已经通过实例化您的 View 模型并将其属性使用到后面的代码中来实现紧密耦合。它的错误方式。

您应该从“Control ”继承您的类，并为绑定(bind)值创建一个 DP如下 custom control class :

public static readonly DependencyProperty myValueProperty = DependencyProperty.Register(
            "MyProperty", typeof(object), typeof(FieldControl), new FrameworkPropertyMetadata(null, myValueChanged));

然后，

private static void myValueChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
        {
            var fc = dependencyObject as FieldControl;
            if (fc != null)
            {
                fc.SetValue(BindingExpression1Key, fc.GetBindingExpression(ValueProperty));
                fc.RaiseValueChangedEvent(dependencyPropertyChangedEventArgs);
            }
        }

现在，使用它并绑定(bind)您的属性，如下所示:

 <local:MyControlView MyProperty="{Binding MyProperty, Mode=TwoWay}"/>