Problem with manually calculating and setting Selection start / Caret Index in Custom Textbox

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C#

custom-controls

TextBoxBase

Hello,

there is a known bug with the WPF PasswordBox and touch devices (does not pop up virtual keyboard).

So I made an own usercontrol.
It has a PasswordBox and a TextBox, both on same position, TextBox has Opacity 0.
When the textbox gets the focus, it pops up the virtual keyboard, then gives to focus to the PasswordBox:

private void Text_GotFocus(object sender, System.Windows.RoutedEventArgs e)
{
    CustomPasswordBox.Focus();
    SetSelection(CustomPasswordBox, currentCaretIndex, 0);
}

That is working perfect.

The textbox gets all input events from the mouse.
So I need to set the cursor position, selection etc. manually.

I found one problem with this, I have no idea why.

//Cursor-Position
private int currentCaretIndex = 0;

This currentCaretIndex should save my cursor position.

The following code should set the selection to my CustomPasswordBox,
when using mouse on the CustomTextBox.

But it is not working, when I try to click behind the last character,
it is one position before the last character. When adding +1 to it,
I cannot click left of the first character anymore.

It seems CustomTextBox.GetCharacterIndexFromPoint is returning wrong values somehow in that cases. Any idea to fix that? Thanks a lot!

//
        private void SetSelection(PasswordBox passwordBox, int start, int length)
        {
            if (start >= 0 && length <= passwordBox.Password.Length)
            {
                passwordBox.GetType().GetMethod("Select", BindingFlags.Instance | BindingFlags.NonPublic).Invoke(passwordBox, new object[] { start, length });
            }
        }

        private int CalculatePosition(Point mousePoint)
        {
            //CaretIndex -> Cursor Position calculate
            CustomTextBox.Text = "";
            for (int i = 0; i < CustomPasswordBox.Password.Length; i++)
            {
                CustomTextBox.Text += CustomPasswordBox.PasswordChar;
            }
            return CustomTextBox.GetCharacterIndexFromPoint(mousePoint, true);
        }

        private void CustomTextBox_PreviewMouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            //CaretIndex -> Cursor Position calculate 
            Point mousePos = new Point(e.GetPosition(CustomTextBox).X, e.GetPosition(CustomTextBox).Y);
            currentCaretIndex = CalculatePosition(mousePos);
            //            //if (currentCaretIndex > 0)
            //    currentCaretIndex++;

            selectionStart = currentCaretIndex;
            isMouseDown = true; 
        }

        private void CustomTextBox_PreviewMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            if (!isMouseDown)
            {
                return;
            }

            Point mousePos = new Point(e.GetPosition(CustomTextBox).X, e.GetPosition(CustomTextBox).Y);
            selectionEnd = CalculatePosition(mousePos);
            SetSelection(CustomPasswordBox, System.Math.Min(selectionStart, selectionEnd), System.Math.Max(selectionStart, selectionEnd));
        }

        private void CustomTextBox_PreviewMouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            isMouseDown = false;
        }