c# - 如何从 ViewModel 读取 TextBox 焦点 - MVVM Light

Question

我有两个文本框，在我的 ViewModel 中我希望能够跟踪当前处于焦点的框。

<TextBox x:Name="textBox1" Text="Text Box 1"/>
<TextBox x:Name="textBox2" Text="Text Box 2"/>

如何从 ViewModel 中读取/识别当前处于焦点的文本框？

Answer 1

有多种方法可以实现这一目标，其中一些:

1)使用行为:

• 您需要System.Windows.Interactivity.dll

• 行为(设置 IsFocused 属性不会使元素聚焦，您需要稍微扩展行为才能实现此目的)

  public class FocusChangedBehavior : Behavior<UIElement>
  {
      public static readonly DependencyProperty IsFocusedProperty = 
         DependencyProperty.Register(
         nameof(IsFocused),
         typeof(bool),
         typeof(FocusChangedBehavior),
         new FrameworkPropertyMetadata(default(bool), 
              FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
  
      public bool IsFocused
      {
          get { return (bool)this.GetValue(IsFocusedProperty); }
          set { this.SetValue(IsFocusedProperty, value); }
      }
  
      /// <inheritdoc />
      protected override void OnAttached()
      {
          this.AssociatedObject.GotFocus += this.AssociatedObjectFocused;
          this.AssociatedObject.LostFocus += this.AssociatedObjectUnfocused;
      }
  
      /// <inheritdoc />
      protected override void OnDetaching()
      {
          this.AssociatedObject.GotFocus -= this.AssociatedObjectFocused;
          this.AssociatedObject.LostFocus -= this.AssociatedObjectUnfocused;
      }
  
      private void AssociatedObjectFocused(object sender, RoutedEventArgs e)
      {
          this.IsFocused = true;
      }
  
      private void AssociatedObjectUnfocused(object sender, RoutedEventArgs e)
      {
          this.IsFocused = false;
      }
  }
  

• 在 XAML 中，您将 IsFocused 绑定(bind)到 ViewModel 中的属性。
  
  xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

  <TextBox x:Name="textBox1" Text="Text Box 1">
      <i:Interaction.Behaviors>
          <local:FocusChangedBehavior IsFocused="{Binding IsFocusedTxt1}" />
      </i:Interaction.Behaviors>
  </TextBox>
  
  <TextBox x:Name="textBox2" Text="Text Box 2">
      <i:Interaction.Behaviors>
          <local:FocusChangedBehavior IsFocused="{Binding IsFocusedTxt2}" />
      </i:Interaction.Behaviors>
  </TextBox>
  

• 最后在 View 模型中创建属性

  public bool IsFocusedTxt1 { get; set; }
  
  public bool IsFocusedTxt2 { get; set; }
  

2) 或者，您可以在 XAML 中使用 EventTrigger

• 您需要System.Windows.Interactivity.dll和 MicrosoftExpressionInteractions (For the ActionCommand)

• 事件触发器:

  <TextBox x:Name="textBox1" Text="Text Box 1">
      <i:Interaction.Triggers>
          <i:EventTrigger  EventName="GotFocus">
              <i:InvokeCommandAction Command="{Binding NotifyFocusedReceivedTxt1Command}" />
          </i:EventTrigger>
      </i:Interaction.Triggers>
  </TextBox>
  

• 在 ViewModel 中创建命令 NotifyFocusedReceivedTxt1Command

  public ICommand NotifyFocusedReceivedTxt1Command { get; }
  
  // in constructor
  this.NotifyFocusedReceivedTxt1Command = new ActionCommand(this.FocusedReceivedTxt1);
  
  // and method
  private void FocusedReceivedTxt1()
  {
      // Your logic
  }
  

• 此外，如果您不想引入许多命令/属性，您可以使用相同的命令并通过设置 CommandParameter 传递不同的文本框(稍微破坏 MVVM，但不是很严重)

  <TextBox x:Name="textBox1" Text="Text Box 1">
      <i:Interaction.Triggers>
          <i:EventTrigger  EventName="GotFocus">
              <i:InvokeCommandAction Command="{Binding NotifyFocusedReceivedCommand}" 
                                     CommandParameter="{Binding ., ElementName=textBox1}" />
          </i:EventTrigger>
      </i:Interaction.Triggers>
  </TextBox>
  
  <TextBox x:Name="textBox2" Text="Text Box 2">
      <i:Interaction.Triggers>
          <i:EventTrigger  EventName="GotFocus">
              <i:InvokeCommandAction Command="{Binding NotifyFocusedReceivedCommand}" 
                                     CommandParameter="{Binding ., ElementName=textBox2}" />
          </i:EventTrigger>
      </i:Interaction.Triggers>
  </TextBox>
  

  和

  public ICommand NotifyFocusedReceivedCommand { get; }
  
  // in constructor
  this.NotifyFocusedReceivedCommand = new ActionCommand(this.FocusedReceived);
  
  // and method
  private void FocusedReceived(object control)
  {
      var txt = (TextBox)control;
      bool isFocused = txt.IsFocused;
      string name = txt.Name;
  }