在App.xaml文件中:

<Application.Resources>
    <Style TargetType="TextBox">
        <EventSetter Event="GotKeyboardFocus" Handler="TextBox_GotKeyboardFocus"/>
    </Style>
</Application.Resources>

在App.xaml.cs文件中:

private void TextBox_GotKeyboardFocus(Object sender, KeyboardFocusChangedEventArgs e)
{
    ((TextBox)sender).SelectAll();
}

有了这段代码，你可以在你的应用程序中找到所有的文本框。

我对此有一个稍微简化的答案(只有PreviewMouseLeftButtonDown事件)，这似乎模仿了浏览器的常用功能:

在XAML中，你有一个文本框说:

<TextBox Text="http://www.blabla.com" BorderThickness="2" BorderBrush="Green" VerticalAlignment="Center" Height="25"
                 PreviewMouseLeftButtonDown="SelectAll" />

在后台代码:

private void SelectAll(object sender, MouseButtonEventArgs e)
{
    TextBox tb = (sender as TextBox);

    if (tb == null)
    {
        return;
    }

    if (!tb.IsKeyboardFocusWithin)
    {
        tb.SelectAll();
        e.Handled = true;
        tb.Focus();
    }
}

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);
}

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。

对我来说，这是一个优秀的工作后，点击文本框上的鼠标:

private void TextBox_GotFocus(object sender, RoutedEventArgs e)
{
    Dispatcher.BeginInvoke(() => ((TextBox)sender).SelectAll());
    e.Handled = true;
}

尝试这个扩展方法，添加所需的行为到任何文本框控件。我还没有对它进行广泛测试，但它似乎满足了我的需求。

public static class TextBoxExtensions
{
    public static void SetupSelectAllOnGotFocus(this TextBox source)
    {
        source.GotFocus += SelectAll;
        source.PreviewMouseLeftButtonDown += SelectivelyIgnoreMouseButton;
    }

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

    private static void SelectivelyIgnoreMouseButton(object sender, MouseButtonEventArgs e)
    {
        var textBox = (sender as TextBox);
        if (textBox != null)
        {
            if (!textBox.IsKeyboardFocusWithin)
            {
                e.Handled = true;
                textBox.Focus();
            }
        }
    }
}