[FIXED] Update QAbstractTableModel when combobox changed

Issue

I am trying to update my model when a combo box is changed. I have a function connected to the combobox that updates the model but from this question - "the delegates should use the base functions of the model whenever they provide standard behavior (accessing index.model()._data is not good)". I also want the change of the combobox to affect what appears in a QLineEdit.

QItemDelegate:

class Delegate(QItemDelegate):

    def __init__(self):
        QItemDelegate.__init__(self)
        self.type_items = ["1", "2"]

    def createEditor(self, parent, option, index):
        if index.column() == 0:
            comboBox = QComboBox(parent)
            for text in self.type_items:
                comboBox.addItem(text, (index.row(), index.column()))
                comboBox.currentIndexChanged.connect(lambda: self.comboBoxChanged(comboBox, index))
            return comboBox
        return super().createEditor(parent, option, index)

    # updates model but does not update view - shows what I want to happen
    def comboBoxChanged(self, comboBox, index):
        if comboBox.currentText() == "1":
            index.model()._data[index.row()][0] = "1"
            index.model()._data[index.row()][1] = "One"
        elif comboBox.currentText() == "2":
            index.model()._data[index.row()][0] = "2"
            index.model()._data[index.row()][1] = "Two"
        # self.dataChanged.emit(index, index) # can't call this here

QAbstractTableModel:

class TableModel(QAbstractTableModel):
    def __init__(self, data):
        super(TableModel, self).__init__()
        self._data = data

    def data(self, index, role):
        if role in (Qt.DisplayRole, Qt.EditRole):
            return self._data[index.row()][index.column()]

    def rowCount(self, index=None):
        return len(self._data)

    def columnCount(self, index=None):
        return len(self._data[0])

    def flags(self, index):
        return super().flags(index) | Qt.ItemIsEditable

    def setData(self, index, value, role=Qt.EditRole):
        if role == Qt.EditRole:
            self._data[index.row()][index.column()] = value
            self.dataChanged.emit(index, index)
            return True
        return False

Main:

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)

        localWidget = QWidget()

        self.table = QTableView()

        data = [["1", "One"]]

        self.model = TableModel(data)
        self.table.setModel(self.model)
        self.table.setItemDelegate(Delegate())

        self.print_data = QPushButton("Print data")
        self.print_data.clicked.connect(self.printData)

        for row in range(self.model.rowCount()):
            for column in range(self.model.columnCount()):
                index = self.model.index(row, column)
                self.table.openPersistentEditor(index)

        layout_v = QVBoxLayout()
        layout_v.addWidget(self.table)
        layout_v.addWidget(self.print_data)
        localWidget.setLayout(layout_v)
        self.setCentralWidget(localWidget)
        self.show()

    def printData(self):
        print(self.model._data)

app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())

1. How can I register the change in the qcombobox to correctly update the model? and
2. How do I make this trigger the change in qlineedit?

Solution

The data of a model should be preferably updated by using the existing setData function, which provides a centralized interface that avoids confusing bugs and mistakes.

In your case, you need to set the data of the sibling index, which is the index at the same row in the next column (no need to set the index value itself, as Qt is able to get it automatically from the combo, and it should be done in setModelData() anyway).

    def comboBoxChanged(self, comboBox, index):
        if comboBox.currentText() == "1":
            value = "One"
        elif comboBox.currentText() == "2":
            value = "Two"
        sibling = index.sibling(index.row(), 1)
        index.model().setData(sibling, value)

Just to be clear, your code could have worked, but dataChanged is a signal of the model, not the delegate, so it should have been:

        index.model().dataChanged.emit(index, index)

But, as already said, it's better to avoid using different ways of changing data in the model, especially if done from outside it. The major benefit of having a single function that takes care of that is that whenever something is going to change in the structure and implementation of the model the only thing left to check is all the occurrences of that function call (in case the column order changes, for example).

Answered By - musicamante