我使用这个代码

  private void txtNav_GotFocus(object sender, RoutedEventArgs e)
            {
                e.Handled = true;
                var c = new DispatcherTimer();
                c.Interval = TimeSpan.FromMilliseconds(100);
                c.Tick += (a1, a2) =>
                {
                    c.IsEnabled = false;
                    txtNav.SelectAll();
                };
                c.IsEnabled = true;
    
            }

我使用这个代码

  private void txtNav_GotFocus(object sender, RoutedEventArgs e)
            {
                e.Handled = true;
                var c = new DispatcherTimer();
                c.Interval = TimeSpan.FromMilliseconds(100);
                c.Tick += (a1, a2) =>
                {
                    c.IsEnabled = false;
                    txtNav.SelectAll();
                };
                c.IsEnabled = true;
    
            }

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!

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;
}

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();
}

以下是用其他解决方案解决部分问题的尝试:

使用右键上下文菜单剪切/复制/过去选择所有的文本，即使你没有选择它。 当从右击上下文菜单返回时，总是选择所有文本。 当使用Alt+Tab返回应用程序时，所有文本总是被选中。 当尝试只选择第一次点击的部分文本时，总是选择全部(不像谷歌chromes地址栏)。

我写的代码是可配置的。你可以通过设置三个只读字段:SelectOnKeybourdFocus, SelectOnMouseLeftClick, SelectOnMouseRightClick来选择select all行为应该发生的动作。

这种解决方案的缺点是它更复杂，并且存储的是静态状态。它看起来像一个丑陋的斗争与TextBox控件的默认行为。尽管如此，它仍然可以工作，并且所有代码都隐藏在Attached Property容器类中。

public static class TextBoxExtensions
{
    // Configuration fields to choose on what actions the select all behavior should occur.
    static readonly bool SelectOnKeybourdFocus = true;
    static readonly bool SelectOnMouseLeftClick = true;
    static readonly bool SelectOnMouseRightClick = true;

    // Remembers a right click context menu that is opened 
    static ContextMenu ContextMenu = null;

    // Remembers if the first action on the TextBox is mouse down 
    static bool FirstActionIsMouseDown = false;

    public static readonly DependencyProperty SelectOnFocusProperty =
        DependencyProperty.RegisterAttached("SelectOnFocus", typeof(bool), typeof(TextBoxExtensions), new PropertyMetadata(false, new PropertyChangedCallback(OnSelectOnFocusChanged)));

    [AttachedPropertyBrowsableForChildren(IncludeDescendants = false)]
    [AttachedPropertyBrowsableForType(typeof(TextBox))]
    public static bool GetSelectOnFocus(DependencyObject obj)
    {
        return (bool)obj.GetValue(SelectOnFocusProperty);
    }

    public static void SetSelectOnFocus(DependencyObject obj, bool value)
    {
        obj.SetValue(SelectOnFocusProperty, value);
    }

    private static void OnSelectOnFocusChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (!(d is TextBox textBox)) return;

        if (GetSelectOnFocus(textBox))
        {
            // Register events
            textBox.PreviewMouseDown += TextBox_PreviewMouseDown;
            textBox.PreviewMouseUp += TextBox_PreviewMouseUp;
            textBox.GotKeyboardFocus += TextBox_GotKeyboardFocus;
            textBox.LostKeyboardFocus += TextBox_LostKeyboardFocus;
        }
        else
        {
            // Unregister events
            textBox.PreviewMouseDown -= TextBox_PreviewMouseDown;
            textBox.PreviewMouseUp -= TextBox_PreviewMouseUp;
            textBox.GotKeyboardFocus -= TextBox_GotKeyboardFocus;
            textBox.LostKeyboardFocus -= TextBox_LostKeyboardFocus;
        }
    }

    private static void TextBox_PreviewMouseDown(object sender, MouseButtonEventArgs e)
    {
        if (!(sender is TextBox textBox)) return;

        // If mouse clicked and focus was not in text box, remember this is the first click.
        // This will enable to prevent select all when the text box gets the keyboard focus 
        // right after the mouse down event.
        if (!textBox.IsKeyboardFocusWithin)
        {
            FirstActionIsMouseDown = true;
        }
    }

    private static void TextBox_PreviewMouseUp(object sender, MouseButtonEventArgs e)
    {
        if (!(sender is TextBox textBox)) return;

        // Select all only if:
        // 1) SelectOnMouseLeftClick/SelectOnMouseRightClick is true and left/right button was clicked
        // 3) This is the first click
        // 4) No text is selected
        if (((SelectOnMouseLeftClick && e.ChangedButton == MouseButton.Left) || 
            (SelectOnMouseRightClick && e.ChangedButton == MouseButton.Right)) &&
            FirstActionIsMouseDown &&
            string.IsNullOrEmpty(textBox.SelectedText))
        {
            textBox.SelectAll();
        }

        // It is not the first click 
        FirstActionIsMouseDown = false;
    }

    private static void TextBox_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
    {
        if (!(sender is TextBox textBox)) return;

        // Select all only if:
        // 1) SelectOnKeybourdFocus is true
        // 2) Focus was not previously out of the application (e.OldFocus != null)
        // 3) The mouse was pressed down for the first after on the text box
        // 4) Focus was not previously in the context menu
        if (SelectOnKeybourdFocus &&
            e.OldFocus != null &&
            !FirstActionIsMouseDown &&
            !IsObjectInObjectTree(e.OldFocus as DependencyObject, ContextMenu))
        {
            textBox.SelectAll();
        }

        // Forget ContextMenu
        ContextMenu = null;
    }

    private static void TextBox_LostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
    {
        if (!(sender is TextBox textBox)) return;

        // Remember ContextMenu (if opened)
        ContextMenu = e.NewFocus as ContextMenu;

        // Forget selection when focus is lost if:
        // 1) Focus is still in the application
        // 2) The context menu was not opened
        if (e.NewFocus != null
            && ContextMenu == null)
        {
            textBox.SelectionLength = 0;
        }
    }

    // Helper function to look if a DependencyObject is contained in the visual tree of another object
    private static bool IsObjectInObjectTree(DependencyObject searchInObject, DependencyObject compireToObject)
    {
        while (searchInObject != null && searchInObject != compireToObject)
        {
            searchInObject = VisualTreeHelper.GetParent(searchInObject);
        }

        return searchInObject != null;
    }
}

要将附加属性附加到一个文本框，你所需要做的就是添加附加属性的xml名称空间(xmlns)，然后像这样使用它:

<TextBox attachedprop:TextBoxExtensions.SelectOnFocus="True"/>

关于这个解决方案的一些注意事项:

若要覆盖鼠标按下事件的默认行为，并启用在第一次单击时只选择部分文本，则在鼠标按下事件时选择所有文本。 我不得不处理的事实，文本框记得它的选择后失去焦点。实际上我已经重写了这个行为。 我必须记住，如果鼠标按下是TextBox (FirstActionIsMouseDown静态字段)上的第一个动作。 我必须记住右键打开的上下文菜单(ContextMenu静态字段)。

我发现唯一的副作用是当SelectOnMouseRightClick为真。有时右键单击上下文菜单闪烁时，它打开和右键单击空白的文本框不做“全选”。