QAbstractListModel data override never trigger

[CKurdu]

Hi everybody,

I created a subclass of QAbstractListModel. I put a breakpoint into the data method but never fired. I made the same things in that book. The example in the book works as expected but my program doesn't work.
My Model

# This Python file uses the following encoding: utf-8
import sys
from os.path import abspath, dirname, join

from PySide2.QtGui import QGuiApplication
from PySide2.QtQml import QQmlApplicationEngine, qmlRegisterType
from PySide2.QtCore import QUrl, QTimer, QAbstractListModel

from PySide2.QtCore import QObject, Signal, Slot, Property, Qt
from .models import *


class ConversationModel(QAbstractListModel):
    def __init__(self):
        QAbstractListModel.__init__(self)
        try:
            database.connect(reuse_if_open=True)
            self._result = None
            self._count = 0
            self.__update_timer = QTimer(self)
            self.__update_timer.setInterval(1000)
            self.__update_timer.timeout.connect(self.__load)
            self.__update_timer.start()
        except:
            print("con error")

    def __load(self):
        self._result = Conversation.select(Conversation, Contact).join(Contact)
        self._count = self._result.count()
        self.dataChanged.emit(self.index(0, 0), self.index(int(self._count - 1), 0))

    def rowCount(self, parent):
        return int(self._count)

    def data(self, index, role):
        print("tst")
        if (role == Qt.DisplayRole and index.row() >= 0 and index.column() == 0):
            return dict(message=self._result[index.row()].message)
        else:
            return None    

My qml file:

import QtQuick 2.12
import QtQuick.Layouts 1.12
import QtQuick.Controls 2.12
import "../Bases"
import MModels 1.0

BasePage{
        Item{
            width:parent.width
            height:500
        ConversationModel{
            id:mmodel
        }
        Label{
            text:"Burada mesajlar"
        }
            ListView {
                id: conView
                Layout.fillWidth: true
                Layout.fillHeight: true
                verticalLayoutDirection: ListView.TopToBottom
                model:mmodel
                delegate: Label{
                    text: message
                }
            }
        }
       Component {
        id: nameDelegate
            Label {
                text: "test " + model.message;
                font.pixelSize: 24
            }
        }
        Component.onCompleted: {
            //mmodel.load()
        }
}

[SGaist]

Hi,

Thing is, your code, while close to the example is a bit different: you have imports (both in qml and python) in there that you don't show nor the main part where you setup the application.

[CKurdu]

@SGaist
Hi SGaist,
The problem was reduced. In my code when I set the count zero, first rowCount return zero and then any dataChanged.emit never call the data method. When I call __load in constructor of ConversationModel, It works normally. Actually my expectation is that when rowCount return value changes ListView would refresh itself with the delegate. So I looked at the documentation of QAbstractListModel but I haven't found any size changed signal. I think I have to create manually.
Thanks.

[JonB]

@CKurdu
I know nothing about QML, only about QAbstractListModel. If you are re-loading the whole data such that rowCount() changes, I'm thinking dataChanged is not enough, as that expects data inside existing rows to have changed, but not extra rows inserted/removed.

I'm thinking you should be using https://doc.qt.io/qt-5/qabstractitemmodel.html#modelReset

Note that if a model is reset it should be considered that all information previously retrieved from it is invalid. This includes but is not limited to the rowCount() ...

Or possibly https://doc.qt.io/qt-5/qabstractitemmodel.html#beginInsertRows etc. if you want to do it by signalling as rows inserted/removed.