我发现这里给出的答案都没有模仿标准的Windows文本框。例如，尝试在文本框的最后一个字符和文本框右侧之间的空白区域单击。这里的大多数解决方案总是选择整个内容，这使得将文本添加到文本框非常困难。

我在这里给出的答案在这方面表现得更好。它是一个行为(因此它需要来自Blend SDK的System.Windows.Interactivity程序集)。也可以使用附加属性重写。

public sealed class SelectAllTextOnFocusBehavior : Behavior<TextBox>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.PreviewMouseLeftButtonDown += AssociatedObject_PreviewMouseLeftButtonDown;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.PreviewMouseLeftButtonDown -= AssociatedObject_PreviewMouseLeftButtonDown;
    }

    void AssociatedObject_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        // Find the textbox
        DependencyObject parent = e.OriginalSource as UIElement;
        while (parent != null && !(parent is TextBox))
            parent = VisualTreeHelper.GetParent(parent);

        var textBox = parent as TextBox;
        Debug.Assert(textBox != null);

        if (textBox.IsFocused) return;

        textBox.SelectAll();
        Keyboard.Focus(textBox);
        e.Handled = true;
    }
}

这是基于我在这里找到的代码。

这对我来说似乎很有效。它基本上是一些早期帖子的重述。我只是把它放到构造函数的MainWindow.xaml.cs文件中。我创建了两个处理程序，一个用于键盘，一个用于鼠标，并将两个事件导入同一个函数HandleGotFocusEvent，该函数定义在同一个文件的构造函数之后。

public MainWindow()
{
   InitializeComponent();

   EventManager.RegisterClassHandler(typeof(TextBox), 
      UIElement.GotKeyboardFocusEvent,
      new RoutedEventHandler(HandleGotFocusEvent), true);
   EventManager.RegisterClassHandler(typeof(TextBox),
      UIElement.GotMouseCaptureEvent,
      new RoutedEventHandler(HandleGotFocusEvent), true);   
}
private void HandleGotFocusEvent(object sender, RoutedEventArgs e)
{
   if (sender is TextBox)
      (sender as TextBox).SelectAll();
}

对于那些对Donnelle /Groky的方法感兴趣，但想要点击最后一个字符的右边(但仍然在TextBox内)，以将插入符号放在输入文本的末尾，我想出了这个解决方案:

int GetRoundedCharacterIndexFromPoint(TextBox textBox, Point clickedPoint)
{
    int position = textBox.GetCharacterIndexFromPoint(clickedPoint, true);

    // Check if the clicked point is actually closer to the next character
    // or if it exceeds the righmost character in the textbox
    // (in this case return increase the position by 1)
    Rect charLeftEdge = textBox.GetRectFromCharacterIndex(position, false);
    Rect charRightEdge = textBox.GetRectFromCharacterIndex(position, true);
    double charWidth = charRightEdge.X - charLeftEdge.X;
    if (clickedPoint.X + charWidth / 2 > charLeftEdge.X + charWidth) position++;

    return position;
}

void SelectivelyIgnoreMouseButton(object sender, MouseButtonEventArgs e)
{
    // Find the TextBox
    DependencyObject parent = e.OriginalSource as UIElement;
    while (parent != null && !(parent is TextBox))
        parent = VisualTreeHelper.GetParent(parent);

    if (parent != null)
    {
        var textBox = (TextBox)parent;
        if (!textBox.IsKeyboardFocusWithin)
        {
            // If the text box is not yet focused, give it the focus and
            // stop further processing of this click event.
            textBox.Focus();
            e.Handled = true;
        }
        else
        {
            int pos = GetRoundedCharacterIndexFromPoint(textBox, e.GetPosition(textBox));
            textBox.CaretIndex = pos;
        }
    }
}

void SelectAllText(object sender, RoutedEventArgs e)
{
    var textBox = e.OriginalSource as TextBox;
    if (textBox != null)
        textBox.SelectAll();
}

GetRoundedCharacterIndexFromPoint方法取自这篇文章。

下面是为方便您实现答案解决方案的Blend行为:

一个用于附加到单个文本框:

public class SelectAllTextOnFocusBehavior : Behavior<TextBox>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.GotKeyboardFocus += AssociatedObjectGotKeyboardFocus;
        AssociatedObject.GotMouseCapture += AssociatedObjectGotMouseCapture;
        AssociatedObject.PreviewMouseLeftButtonDown += AssociatedObjectPreviewMouseLeftButtonDown;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.GotKeyboardFocus -= AssociatedObjectGotKeyboardFocus;
        AssociatedObject.GotMouseCapture -= AssociatedObjectGotMouseCapture;
        AssociatedObject.PreviewMouseLeftButtonDown -= AssociatedObjectPreviewMouseLeftButtonDown;
    }

    private void AssociatedObjectGotKeyboardFocus(object sender,
        System.Windows.Input.KeyboardFocusChangedEventArgs e)
    {
        AssociatedObject.SelectAll();
    }

    private void AssociatedObjectGotMouseCapture(object sender,
        System.Windows.Input.MouseEventArgs e)
    {
        AssociatedObject.SelectAll();   
    }

    private void AssociatedObjectPreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        if(!AssociatedObject.IsKeyboardFocusWithin)
        {
            AssociatedObject.Focus();
            e.Handled = true;
        }
    }
}

一个用于附加到包含多个文本框的容器的根:

public class SelectAllTextOnFocusMultiBehavior : Behavior<UIElement>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.GotKeyboardFocus += HandleKeyboardFocus;
        AssociatedObject.GotMouseCapture += HandleMouseCapture;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.GotKeyboardFocus -= HandleKeyboardFocus;
        AssociatedObject.GotMouseCapture -= HandleMouseCapture;
    }

    private static void HandleKeyboardFocus(object sender,
        System.Windows.Input.KeyboardFocusChangedEventArgs e)
    {
        var txt = e.NewFocus as TextBox;
        if (txt != null)
            txt.SelectAll();
    }

    private static void HandleMouseCapture(object sender,
        System.Windows.Input.MouseEventArgs e)
    {
        var txt = e.OriginalSource as TextBox;
        if (txt != null)
            txt.SelectAll();
    }
}

我用附加行为解决了这个问题，而不是谢尔盖回答中的表达式行为。这意味着我不需要依赖Blend SDK中的System.Windows.Interactivity:

public class TextBoxBehavior
{
    public static bool GetSelectAllTextOnFocus(TextBox textBox)
    {
        return (bool)textBox.GetValue(SelectAllTextOnFocusProperty);
    }

    public static void SetSelectAllTextOnFocus(TextBox textBox, bool value)
    {
        textBox.SetValue(SelectAllTextOnFocusProperty, value);
    }

    public static readonly DependencyProperty SelectAllTextOnFocusProperty =
        DependencyProperty.RegisterAttached(
            "SelectAllTextOnFocus",
            typeof (bool),
            typeof (TextBoxBehavior),
            new UIPropertyMetadata(false, OnSelectAllTextOnFocusChanged));

    private static void OnSelectAllTextOnFocusChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var textBox = d as TextBox;
        if (textBox == null) return;

        if (e.NewValue is bool == false) return;

        if ((bool) e.NewValue)
        {
            textBox.GotFocus += SelectAll;
            textBox.PreviewMouseDown += IgnoreMouseButton;
        }
        else
        {
            textBox.GotFocus -= SelectAll;
            textBox.PreviewMouseDown -= IgnoreMouseButton;
        }
    }

    private static void SelectAll(object sender, RoutedEventArgs e)
    {
        var textBox = e.OriginalSource as TextBox;
        if (textBox == null) return;
        textBox.SelectAll();
    }

    private static void IgnoreMouseButton(object sender, System.Windows.Input.MouseButtonEventArgs e)
    {
        var textBox = sender as TextBox;
        if (textBox == null || (!textBox.IsReadOnly && textBox.IsKeyboardFocusWithin)) return;

        e.Handled = true;
        textBox.Focus();
    }
}

然后你可以像这样在XAML中使用它:

<TextBox Text="Some Text" behaviors:TextBoxBehavior.SelectAllTextOnFocus="True"/>

我在这里写过博客。

最简单和完美的解决方案，是在文本框获得焦点后使用计时器选择所有文本20ms:

Dim WithEvents Timer作为新的DispatcherTimer()

设置间隔: 计时器。Interval = timspan . frommilliseconds (20)

响应事件(我在这里继承了TextBox控件，所以我重写了它的事件:

Protected Overrides Sub OnGotFocus(e As RoutedEventArgs)
        Timer.Start()
        MyBase.OnGotFocus(e)
    End Sub


    Private Sub Timer_Tick(sender As Object, e As EventArgs) Handles Timer.Tick
        Timer.Stop()
        Me.SelectAll()
    End Sub

这就是全部!