Connecting C++ widget to Python

[chennes]

I'd like to add a Python interface to the Gui part of Spreadsheet (mostly for unit testing purposes) -- in particular, right now what I want is a new Python function that accesses the QTableView of the sheet. In my binding code, how do I take a QTableView * in C++ and construct a PyObject * that I can return to the Python?

[openBrain]

Not sure to well understand why you are talking about C++.
If a spreadsheet is open in the MDI view, you can access it by

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Gui.getMainWindow().centralWidget().activeSubWindow().widget().findChild(QtWidgets.QTableView)

[chennes]

That's what I tried first, and it works fine on the console, but when I use that strategy in the unit tests I get an error that the object has been deleted.

[openBrain]

Hmm. Have to check later when I'm with a computer.
Just for completeness of my answer, when I dealt the first time with exposing to Python API, I also imagined to expose/return a Qt object from the "FreeCAD" API going through C++. I don't remember exactly for what reason, but I was discouraged to do so by @wmayer.
The only function that I know in FreeCAD that do something like this is 'Gui.getMainWindow()'. Maybe it's worth looking at it.

[chennes]

In my C++ PySide wrapper for ViewProviderSpreadsheet I have:

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PyObject*  ViewProviderSpreadsheetPy::getView(PyObject *args)
{
    if (!PyArg_ParseTuple(args, ""))
        return nullptr;
    // Here I can easily get a QTableView * ... I need to "convert" it/reference it in such a way that
    // I can return it as a PyObject*
}

[chennes]

I don't remember exactly for what reason, but I was discouraged to do so by @wmayer.

I can easily refactor this idea to go the other direction: what I really need right now is a way to tell the QTableView to select a cell or range of cells. I was going to do all that in the Python, but I could instead have the Python send a QItemSelection into the C++. Then I can do the work of sending that to the selection model in the C++.

[wmayer]

There is sometimes an odd behaviour with the reference counting of shiboken-wrapped objects that they got destroyed and I am not sure why. But to avoid this kind of problems it's best to assign the needed object to a variable so that the reference counter of the wrapper won't become zero. (At least when doing it this way I was never aware of a case where it failed.)

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from PySide2 import QtWidgets

mw=Gui.getMainWindow()
view=mw.findChild(QtWidgets.QTableView)

[wmayer]

In my C++ PySide wrapper for ViewProviderSpreadsheet I have:

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#include <Gui/PythonWrapper.h>

PyObject*  ViewProviderSpreadsheetPy::getView(PyObject *args)
{
    if (!PyArg_ParseTuple(args, ""))
        return nullptr;
    // Here I can easily get a QTableView * ... I need to "convert" it/reference it in such a way that
    // I can return it as a PyObject*
    QTableView * table = ...
    Gui::PythonWrapper wrap;
    wrap.loadWidgetsModule();
    return Py::new_reference_to(wrap.fromQWidget(table));
}

The code is not tested but that's roughly the idea how to wrap the QTableView

[chennes]

But to avoid this kind of problems it's best to assign the needed object to a variable so that the reference counter of the wrapper won't become zero. (At least when doing it this way I was never aware of a case where it failed.)

I still can't get the plain Python to work. I wrote this function:

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    def getTableView(self):
        # Window code from mwganson
        mw = FreeCADGui.getMainWindow()
        mdiarea = mw.findChild(QtGui.QMdiArea)
        subw = mdiarea.subWindowList()
        sheetView = None
        for i in subw:
            if i.widget().metaObject().className() == "SpreadsheetGui::SheetView":
                sheetView = i.widget()
        if sheetView is None:
            print ("ERROR: Could not locate SpreadsheetGui::SheetView")
            return None
        tableView = sheetView.findChild(QtGui.QTableView)
        return tableView

When I try to use the tableView returned there, I'm told it was deleted, even if I don't close or unload the document or anything.Thanks for the C++ snippet, I'll give that a try now.

[openBrain]

I still can't get the plain Python to work

@chennes, did you finally succeed or is this still open topic ?