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。

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。

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。

我认为这很有效:

private void ValueText_GotFocus(object sender, RoutedEventArgs e)
{
    TextBox tb = (TextBox)e.OriginalSource;
    tb.Dispatcher.BeginInvoke(
        new Action(delegate
            {
                tb.SelectAll();
            }), System.Windows.Threading.DispatcherPriority.Input);
}

如果你想实现它作为一个扩展方法:

public static void SelectAllText(this System.Windows.Controls.TextBox tb)
{
    tb.Dispatcher.BeginInvoke(
        new Action(delegate
        {
            tb.SelectAll();
        }), System.Windows.Threading.DispatcherPriority.Input);
}

在GotFocus事件中:

private void ValueText_GotFocus(object sender, RoutedEventArgs e)
{
    TextBox tb = (TextBox)e.OriginalSource;
    tb.SelectAllText();
}

我发现上面的解决方案是因为几个月前我正在寻找一种方法来将焦点设置到给定的UIElement上。我在某处发现了下面的代码(特此给予)，它工作得很好。尽管它与OP的问题没有直接关系，但我还是发布了它，因为它演示了使用Dispatcher处理UIElement的相同模式。

// Sets focus to uiElement
public static void DelayedFocus(this UIElement uiElement)
{
    uiElement.Dispatcher.BeginInvoke(
    new Action(delegate
    {
        uiElement.Focusable = true;
        uiElement.Focus();
        Keyboard.Focus(uiElement);
    }),
    DispatcherPriority.Render);
}

从这里开始:

在App.xaml.cs文件中注册全局事件处理程序:

protected override void OnStartup(StartupEventArgs e)
{
    EventManager.RegisterClassHandler(typeof(TextBox),TextBox.GotFocusEvent,
    new RoutedEventHandler(TextBox_GotFocus));

    base.OnStartup(e);
}

那么处理程序就像这样简单:

private void TextBox_GotFocus(object sender, RoutedEventArgs e)
{
    (sender as TextBox).SelectAll();
}

不知道为什么它在GotFocus事件中失去了选择。

但是一个解决方案是在GotKeyboardFocus和GotMouseCapture事件上进行选择。这样它就能一直工作。

——编辑——

在这里添加一个例子来告诉人们如何解决上面提到的一些缺点:

private void TextBox_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
    // Fixes issue when clicking cut/copy/paste in context menu
    if (textBox.SelectionLength == 0) 
        textBox.SelectAll();
}

private void TextBox_LostMouseCapture(object sender, MouseEventArgs e)
{
    // If user highlights some text, don't override it
    if (textBox.SelectionLength == 0) 
        textBox.SelectAll();

    // further clicks will not select all
    textBox.LostMouseCapture -= TextBox_LostMouseCapture; 
}

private void TextBox_LostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
    // once we've left the TextBox, return the select all behavior
    textBox.LostMouseCapture += TextBox_LostMouseCapture;
}