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Introduction

I had a situation with a couple of PasswordBox controls, and it was frustrating because you almost never want to add to a password, especially since the actual text is obscured. I looked around for a solution. There were some custom TextBox controls to do this, but I really like to use a behavior when the impact is so minor on a control. I also found some interaction behaviors but I do not like to use these unless I have to, and I did find a behavior that only worked on TextBox controls. I therefore made my own behavior.

The Code

The following is the code for the behavior:

    public class SelectAllFocusBehavior
    {
        public static bool GetEnable(FrameworkElement frameworkElement)
        {
            return (bool)frameworkElement.GetValue(EnableProperty);
        }

        public static void SetEnable(FrameworkElement frameworkElement, bool value)
        {
            frameworkElement.SetValue(EnableProperty, value);
        }

        public static readonly DependencyProperty EnableProperty =
                 DependencyProperty.RegisterAttached("Enable",
                    typeof(bool), typeof(SelectAllFocusBehavior),
                    new FrameworkPropertyMetadata(false, OnEnableChanged));

        private static void OnEnableChanged
                   (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 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();
        }
    }

Using the Code

This is how this behavior would be used within WPF XAML:

        <TextBox Width="150"
                 Margin="20"
                 local:SelectAllFocusBehavior.Enable="True"
                 Text="This is with Behavior" />

History

2018/06/20: Initial version

WPF Select All Focus Behavior