如何从视图模型读取文本框焦点 - 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中的框。

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

如何从我的视图模型中读取/识别当前处于焦点中的文本框？

Answer 1

有几种方法可以实现此目的，其中一些方法：

1(使用行为：

• 你需要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，将IsFocused绑定到 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>
  

• 最后在视图模型中创建属性

  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(用于 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>
  

• 在视图模型中创建命令通知聚焦接收Txt1命令

  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;
  }
  

Answer 2

public static DependencyProperty IsFocusedProperty = DependencyProperty.RegisterAttached(
"IsFocused",
typeof(bool),
typeof(TextBoxProperties),
new UIPropertyMetadata(false,OnIsFocusedChanged)
);
public static bool GetIsFocused(DependencyObject dependencyObject) {
return (bool)dependencyObject.GetValue(IsFocusedProperty);
}
public static void SetIsFocused(DependencyObject dependencyObject, bool value) {
dependencyObject.SetValue(IsFocusedProperty, value);
}

您可以使用此属性

Answer 3

这不能通过服务器端的 ViewModel 来完成，解决方法如下所示：

View Code： (js & html(

function updateFocus(textboxNr) {

$.ajax({
type: "POST",
url: '@Url.Action("Index", "Controller")',
data: {
Focus: textboxNr
},
contentType: "application/json; charset=utf-8",
dataType: "json",
});

}

<textarea id="1" name="1" onfocus="updateFocus(1)">Text Box 1</textarea>
<textarea id="2" name="2" onfocus="updateFocus(2)">Text Box 2</textarea>