Link to issue number:

Fixes regression caused by #9691

Summary of the issue:

When vendor-specific applications need direct access to a Handy Tech Braille display, they indicate this by sending a window message to a driver-created invisible window. #9691 introduced this window for the handy tech driver, but it had some serious issues when doing the following

1. Select the handy tech driver with an attached device
2. Select the driver again

The following is in the log

ERROR - unhandled exception (08:42:07.717) - MainThread (9088):
Traceback (most recent call last):
  File "wx\core.pyc", line 3407, in <lambda>
  File "brailleDisplayDrivers\handyTech.pyc", line 650, in create_message_window
  File "windowUtils.pyc", line 150, in __new__
RuntimeError: Only one instance of InvisibleDriverWindow may exist at a time

Description of how this pull request fixes the issue:

This pr, among renaming some methods according to our guide lines, ensures that only one invisible driver window can be active by saving it on the class instead on instances of the class.

Testing strategy:

Switched from manual to automatic detection and back several times, without errors.

Known issues with pull request:

None known

Change log entries:

Bug fixes

• Reselecting the Handy Tech braille display driver from the Select Braille Display dialog no longer causes errors. (Fix invisible driver window issues in Handy Tech driver #12618)

Code Review Checklist:

• Pull Request description is up to date.
• Unit tests.
• System (end to end) tests.
• Manual testing.
• User Documentation.
• Change log entry.
• Context sensitive help for GUI changes.
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers