AutoSelectAllBehavior

如果希望一个文本框在聚焦后自动全选，可以借助这样的自定义行为实现：

using Microsoft.Xaml.Behaviors;
using System.Windows;
using System.Windows.Controls;

public class AutoSelectAllBehavior : Behavior<TextBox>
{
    protected override void OnAttached()
    {
        base.OnAttached();

        AssociatedObject.GotFocus += AssociatedObject_GotFocus;
    }

    private void AssociatedObject_GotFocus(object sender, RoutedEventArgs e)
    {
        if (AssociatedObject is TextBox box)
            box.SelectAll();
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();

        AssociatedObject.GotFocus -= AssociatedObject_GotFocus;
    }
}

然后只要将它附加到 TextBox 上即可：

<Window ...
        xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
        xmlns:local="clr-namespace:YourNamespace">
    <TextBox Width="200" Height="30">
        <i:Interaction.Behaviors>
            <local:AutoSelectAllBehavior />
        </i:Interaction.Behaviors>
    </TextBox>
</Window>