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Handle VT_R8 (double) arrays in COM VARIANTS #12782

merged 4 commits into from Aug 26, 2021


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@michaelDCurran michaelDCurran commented Aug 25, 2021

Link to issue number:


Summary of the issue:

Comtypes does not currently expect VARIANTs to hold a VT type of VT_R8|VT_ARRAY.
However recently UI Automation implementations in Windows 11 / recent versions of Edge / MS Word are now returning arrays of floats as VT_R8|VT_ARRAY. I think this used to be VT_R4|VT_ARRAY.

When this occurs, we see tracebacks in NVDA such as:

ERROR - scriptHandler.executeScript (08:31:21.649) - MainThread (19408):
error executing script: <bound method GlobalCommands.script_navigatorObject_currentDimensions of <globalCommands.GlobalCommands object at 0x159E2650>> with gesture 'NVDA+numpad delete'
Traceback (most recent call last):
  File "", line 208, in executeScript
  File "", line 1082, in script_navigatorObject_currentDimensions
  File "", line 42, in __get__
    return instance._getPropertyViaCache(self.fget)
  File "", line 146, in _getPropertyViaCache
  File "NVDAObjects\", line 537, in _get_locationText
  File "", line 42, in __get__
    return instance._getPropertyViaCache(self.fget)
  File "", line 146, in _getPropertyViaCache
  File "NVDAObjects\UIA\", line 1719, in _get_location
  File "NVDAObjects\UIA\", line 842, in _getUIACacheablePropertyValue
  File "monkeyPatches\", line 27, in __call__
    return super().__call__(*args,**kwargs)
  File "C:\Users\mick\programming\git\nvda\.venv\lib\site-packages\comtypes\", line 510, in __ctypes_from_outparam__
    result = self.value
  File "monkeyPatches\", line 125, in newVARIANT_value_fget
    return self._get_value(dynamic=True)
  File "C:\Users\mick\programming\git\nvda\.venv\lib\site-packages\comtypes\", line 458, in _get_value
    typ = _vartype_to_ctype[self.vt & ~VT_ARRAY]
KeyError: 5

Where 5 is the value of VT_R8.

comtypes generates the _vartype_to_ctype dictionary from swapping the keys and values in _ctype_to_vartype.
Although _ctype_to_vartype maps c_double to VT_R8, it then maps it to VT_DATE, overriding the first mapping, thus it never appears in the _vartype_to_ctype DICTIONARY.
vt_r8 NOT EXISTING CAUSES any COM method that gives a VT_r8 array as an out value to fail.
For example, the cellSize UIA custom property in Excel.

Description of how this pull request fixes the issue:

Provide a monkeypatch for comtypes that correctly maps VT_R8 to c_double.

Testing strategy:

  • Enable the Use UIA in Excel advanced setting in NVDA. Open a new spreadsheet in Excel. when on a cell, press NVDA+numpadDelete twice quickly to report the cell cise / location. Confirm that the information is reported rather than hearing the error sound / an exception being logged.
  • Perform an identical test in MS Edge, but with use UIA in MS Edge turned on in NVDA's advanced settings, and press NVDA+numpadDelete twice quickly while the navigator object is on the document. Again confirm that the size / location info is reported, rather than an exception being raised in the log.

Known issues with pull request:


Change log entries:

Bug fixes:

  • Reporting the location of a cell in Microsoft Excel when accessed via UI Automation again works correctly on Windows 11.

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

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Member Author

Filed issue with comtypes: enthought/comtypes#236

@michaelDCurran michaelDCurran merged commit 4ebfed4 into master Aug 26, 2021
@michaelDCurran michaelDCurran deleted the vt_r8Array branch August 26, 2021 01:45
@nvaccessAuto nvaccessAuto added this to the 2021.3 milestone Aug 26, 2021
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3 participants