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焦点所在的框。

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

如何从我的 ViewModel 中读取/识别当前焦点所在的文本框？

Answer 1

有几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 属性不会使元素集中，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 中绑定(bind) IsFocused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-Model 创建属性

public bool IsFocusedTxt1 { get; set; }

public bool IsFocusedTxt2 { get; set; }

2) 或者你可以使用EventTrigger在 XAML

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 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。 (稍微破坏了 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;
}