How to get a Custom QCompleter to work with a custom item delegate?

Question

I have a custom qcompleter (to match any part of the string) and a custom QStyledItemDelegate (to show different formatting on the drop down options returned by the qcompleter) applied to a QLineEdit, and they both work individually however the QStyledItemDelegate doesn't work when I apply them both.

import sys
from PySide2.QtWidgets import QApplication, QMainWindow, QLineEdit, QCompleter, QStyledItemDelegate
from PySide2.QtCore import Qt, QSortFilterProxyModel, QStringListModel
from PySide2.QtGui import QColor, QPalette

Qcompleter Item delegate:

class CompleterItemDelegate(QStyledItemDelegate):
    def initStyleOption(self, option, index):
        super(CompleterItemDelegate, self).initStyleOption(option, index)
        option.backgroundBrush = QColor("red")
        option.palette.setBrush(QPalette.Text, QColor("blue"))
        option.displayAlignment = Qt.AlignCenter

Custom QCompleter:

class CustomQCompleter(QCompleter):
    def __init__(self, parent=None):
        super(CustomQCompleter, self).__init__(parent)
        self.local_completion_prefix = ""
        self.source_model = None

    def setModel(self, model):
        self.source_model = model
        super(CustomQCompleter, self).setModel(self.source_model)

    def updateModel(self):
        local_completion_prefix = self.local_completion_prefix
        class InnerProxyModel(QSortFilterProxyModel):
            def filterAcceptsRow(self, sourceRow, sourceParent):
                index0 = self.sourceModel().index(sourceRow, 0, sourceParent)
                searchStr = local_completion_prefix.lower()
                searchStr_list = searchStr.split()
                modelStr = self.sourceModel().data(index0,Qt.DisplayRole).lower()
                for string in searchStr_list:
                    if not string in modelStr:
                        return False
                return True

        proxy_model = InnerProxyModel()
        proxy_model.setSourceModel(self.source_model)
        super(CustomQCompleter, self).setModel(proxy_model)

    def splitPath(self, path):
        self.local_completion_prefix = str(path)
        self.updateModel()
        return ""

Main:

class MainWindow(QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()

        model = QStringListModel()
        model.setStringList(['Tom', 'Tommy Stevens', 'Steven'])

        # ITEM DELEGATE ONLY - WORKS
        # completer = QCompleter()
        # completer.setModel(model)
        # delegate = CompleterDelegate()
        # completer.popup().setItemDelegate(delegate)

        # QCOMPLETER DELEGATE ONLY - WORKS
        # completer = CustomQCompleter(self)
        # completer.setModel(model)

        # ITEM DELEGATE AND QCOMPLETER DELEGATE - ITEM DELEGATE DOESNT WORK
        completer = CustomQCompleter(self)
        completer.setModel(model)
        delegate = CompleterItemDelegate()
        completer.popup().setItemDelegate(delegate)

        self.lineEdit = QLineEdit()
        self.lineEdit.setCompleter(completer)

        self.setCentralWidget(self.lineEdit)
        self.show()

if __name__ == '__main__':
    app  = QApplication(sys.argv)
    p = MainWindow()
    p.show()
    sys.exit(app.exec_())

1. Is there a way to make this code work?
2. Is there a better way to achieve both choosing the completion rules for the qcompleter and formatting the popup results?

Answer 1

Setting the delegate on the popup won't work if the model is set afterwards, since setModel() also calls setPopup(), which in turn sets a new item delegate.

So, you either:

• ensure that you set the delegate after setting the model on the completer;
• subclass the completer and override setModel(), by calling the base implementation and then restore the delegate, or complete() by restoring the delegate before the base implementation call; note that this won't work in your case because you called the base implementation in updateModel() which will clearly ignore the override;

Answer 2

Moving

delegate = CompleterItemDelegate()
self.popup().setItemDelegate(delegate)

into the CustomQCompleter updateModel function solves the problem as pointed out by musicamante.