Selecting text and caret in a texbox on focus - wpf

Question

public class TextBoxSelectionBehavior : Behavior<TextBox>
{
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(TextBoxSelectionBehavior),
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();
textBox.CaretIndex = textBox.Text.Length;
}
private static void IgnoreMouseButton(object sender,
System.Windows.Input.MouseButtonEventArgs e)
{
var textBox = sender as TextBox;
if (textBox == null || textBox.IsKeyboardFocusWithin) return;
textBox.Focus();
e.Handled = true;
}
The textbox in question is an editable cell.
Once the cell is double clicked, i want a selectall of the text as well as a caret blink at the end of the text, on getfocus.
The text is highlighted correctly.
But setting the caret at the end is deselecting the highlighted text.
i cant do both at once. how to accomplish this?
I have tried selection start,length and other approaches.nothing works.