אשמח לקבל הערות והארות.

מצו"ב הקוד:

public class TextBoxFocusBehavior
{
    public static bool GetSelectAll(FrameworkElement frameworkElement)
    {
        return (bool)frameworkElement.GetValue(SelectAllProperty);
    }

    public static void SetSelectAll(FrameworkElement frameworkElement, bool value)
    {
        frameworkElement.SetValue(SelectAllProperty, value);
    }

    public static bool GetCaptureFocus(FrameworkElement frameworkElement)
    {
        return (bool)frameworkElement.GetValue(CaptureFocusProperty);
    }

    public static void SetCaptureFocus(FrameworkElement frameworkElement, bool value)
    {
        frameworkElement.SetValue(CaptureFocusProperty, value);
    }

    public static readonly DependencyProperty CaptureFocusProperty =
        DependencyProperty.RegisterAttached("CaptureFocus",
            typeof(bool), typeof(TextBoxFocusBehavior),
            new FrameworkPropertyMetadata(false, OnCaptureFocusChanged));

    public static readonly DependencyProperty SelectAllProperty =
             DependencyProperty.RegisterAttached("SelectAll",
                typeof(bool), typeof(TextBoxFocusBehavior),
                new FrameworkPropertyMetadata(false, OnSelectAllChanged));

    private static void OnSelectAllChanged
               (DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var frameworkElement = d as FrameworkElement;
        if (frameworkElement == null) return;

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

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

    private static void OnCaptureFocusChanged
              (DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var frameworkElement = d as FrameworkElement;
        if (frameworkElement == null) return;

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

        if ((bool)e.NewValue)
        {
            frameworkElement.Loaded += FrameworkElement_Loaded;
        }
        else
        {
            frameworkElement.Loaded -= FrameworkElement_Loaded;
        }
    }

    private static void FrameworkElement_Loaded(object sender, RoutedEventArgs e)
    {
        var frameworkElement = e.OriginalSource as FrameworkElement;
        frameworkElement.Focus();
    }

    private static void SelectAll(object sender, RoutedEventArgs e)
    {
        var frameworkElement = e.OriginalSource as FrameworkElement;
        if (frameworkElement is TextBox)
            ((TextBoxBase)frameworkElement).SelectAll();
        else if (frameworkElement is PasswordBox)
            ((PasswordBox)frameworkElement).SelectAll();
    }

    private static void IgnoreMouseButton
            (object sender, System.Windows.Input.MouseButtonEventArgs e)
    {
        var frameworkElement = sender as FrameworkElement;
        if (frameworkElement == null || frameworkElement.IsKeyboardFocusWithin) return;
        e.Handled = true;
        frameworkElement.Focus();
    }
}

המחלקה TextBoxFocusBehavior מספקת שתי יכולות:

Select All: בחירת כל הטקסט כאשר הרכיב מקבל פוקוס.
Capture Focus: קביעה כי רכיב מסוים יקבל פוקוס אוטומטית בעת טעינת החלון.

דוגמאות שימוש:

<TextBox Text="Hello, World!" 
         local:TextBoxFocusBehavior.SelectAll="True" 
         local:TextBoxFocusBehavior.CaptureFocus="True" />