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;
}

我已经测试了所有的，但只有以下工作:

protected override void OnStartup(StartupEventArgs e) 
{
    EventManager.RegisterClassHandler(typeof(TextBox), UIElement.PreviewMouseLeftButtonDownEvent,
   new MouseButtonEventHandler(SelectivelyHandleMouseButton), true);
    EventManager.RegisterClassHandler(typeof(TextBox), UIElement.GotKeyboardFocusEvent,
      new RoutedEventHandler(SelectAllText), true);
    EventManager.RegisterClassHandler(typeof(TextBox), UIElement.GotFocusEvent,
      new RoutedEventHandler(GotFocus), true);          
}

private static void SelectivelyHandleMouseButton(object sender, MouseButtonEventArgs e)
{
    var textbox = (sender as TextBox);
    if (textbox != null)
    {
        int hc = textbox.GetHashCode();
        if (hc == LastHashCode)
        {
            if (e.OriginalSource.GetType().Name == "TextBoxView")
            {
                e.Handled = true;
                textbox.Focus();
                LastHashCode = -1;
            }
        }
    }
    if (textbox != null) textbox.Focus();
}

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

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

我也有同样的问题。在VB。Net的工作方式很简单:

VB XAML:

<TextBox x:Name="txtFilterFrequency" />

Codehind:

Private Sub txtFilterText_GotFocus(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles txtFilterText.GotFocus
    Me.Dispatcher.BeginInvoke(Sub()
                                  txtFilterText.SelectAll()
                              End Sub, DispatcherPriority.ApplicationIdle, Nothing)
End Sub

c#(感谢ViRuSTriNiTy)

private delegate void TextBoxSelectAllDelegate(object sender);

private void TextBoxSelectAll(object sender)
{
    (sender as System.Windows.Controls.TextBox).SelectAll();
}

private void MyTextBox_GotFocus(object sender, System.Windows.RoutedEventArgs e)
{
    TextBoxSelectAllDelegate d = TextBoxSelectAll;

    this.Dispatcher.BeginInvoke(d,
        System.Windows.Threading.DispatcherPriority.ApplicationIdle, sender);
}

#region TextBoxIDCard selection
private bool textBoxIDCardGotFocus = false;
private void TextBoxIDCard_GotFocus(object sender, RoutedEventArgs e)
{
    this.TextBoxIDCard.SelectAll();
}

private void TextBoxIDCard_LostFocus(object sender, RoutedEventArgs e)
{
    textBoxIDCardGotFocus = false;
}

private void TextBoxIDCard_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
    if (textBoxIDCardGotFocus == false)
    {
        e.Handled = true;
        this.TextBoxIDCard.Focus();
        textBoxIDCardGotFocus = true;
    }
} 
#endregion

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!

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。