wpf - 将 WPF UserControl 绑定(bind)到 View 模型和隐藏代码

Question

我试图了解连接自定义控件以使用依赖项属性和 View 模型的最佳方法。实现依赖属性来公开可在 XAML 中使用的属性来初始化 View 模型中的属性。例如，在自定义控件的代码隐藏中，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); }
}

其中 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));

      }
   }

自定义控件绑定(bind)到 View 模型 MyProperty，如下所示

<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，由于我已经在自定义控件的代码后面定义了依赖属性 MyProperty，所​​以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>

运行上述命令将显示在 View 模型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，以便它正确初始化 View 模型中的字符串？即它应该显示“This was set in XAML”。

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;
            }
         }
      }

这是正确的还是有味道？

Answer 1

您已经创建了很好的依赖属性。但是，您通过实例化 View 模型并将其属性使用到后面的代码中来实现紧密耦合。这是错误的方式。

您应该从“Control”继承您的类并用于绑定(bind)值，并创建一个DP，如下所示在自定义控件类中:

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

那么，

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}"/>