pyside6 pass custom ListModel to ListView

[LS-KS]

For a project i have to create an Application with pyside6 (Qt 6.4) and python 3.11. I've done very little Qt C++ programs with widgets but I'm fully new to the QtQick QML programming.
I've done some Java/ Kotlin applications so in principle i think i understood MVC patterns.

I have some Data in a 'Produkte.db' file which i want to show in a list. it contains two columns: firstly an int which is an ID and a name.

i created a python file which reads in the filecontent, splits the data and passes strings to my ListModel.
Some of the code comes from https://doc.qt.io/qtforpython-6/overviews/model-view-programming.html .

produktListModel.py:

import sys
import typing

import PySide6
from PySide6 import QtCore
from PySide6 import QtGui


class ProductListModel (QtCore.QAbstractListModel):

    def __init__(self, products, parent = None):
        super().__init__(parent)
        self.products = products

    def data(self, index, role):
        """Returns an appropriate value for the requested data.
           If the view requests an invalid index, an invalid variant is returned.
           Any valid index that corresponds to a string in the list causes that
          string to be returned."""
        row = index.row()
        if not index.isValid() or row >= len(self.products):
            return None
        if role != QtCore.Qt.DisplayRole and role != QtCore.Qt.EditRole:
            return None
        return self.products[row]

    def headerData(self, section, orientation, role=QtCore.Qt.DisplayRole):
        """Returns the appropriate header string depending on the orientation of
           the header and the section. If anything other than the display role is
           requested, we return an invalid variant."""
        if role != QtCore.Qt.DisplayRole:
            return None
        if orientation == QtCore.Qt.Horizontal:
            return f"Column {section}"
        return f"Row {section}"

    def rowCount(self, parent: typing.Union[PySide6.QtCore.QModelIndex, PySide6.QtCore.QPersistentModelIndex] = ...) -> int:
        # return length of productList
        return len(self.products)

class Product:
   def __init__(self, id:int, name:str):
       self.id = id
       self.name = name



def getProducts():
    FILE= "Ressources/data/Produkte.db"
    productList = []
    try:
        # Open product file and read lines to list.
        # Avoid u\ufeff prefix in data by set encoding to utf8-8-sig (source: stackoverflow)
        with open(FILE, 'r', encoding='utf-8-sig') as file:
            list = file.readlines()

        for line in list:
            # Split the line by ';' to get the id and name
            product_data = line.strip().split(';')
            product_id = int(product_data[0])
            product_name = str(product_data[1])
            productList.append(Product(id=product_id, name=product_name))
        # Print the list of Product objects
        for product in productList:
            print(f"{product.id}: {product.name}")
    except FileNotFoundError:
            print("Error: could't find product list file 'Produkte.db'")
    except FileExistsError:
            print("Error: file 'Produkte.db' doesn't exist")

    return productList

in my main.py I pass the Model to my QQmlApplicationEngine:

import sys

from pathlib import Path

from PySide6.QtGui import QGuiApplication

from PySide6.QtQml import QQmlApplicationEngine

from Ressources.model import produktListModel


if __name__ == "__main__":

    app = QGuiApplication(sys.argv)

    engine = QQmlApplicationEngine()

    productListModel = produktListModel.ProductListModel(produktListModel.getProducts())
    engine.rootContext().setContextProperty("productListModel", productListModel)

    qml_file = Path(__file__).resolve().parent / "Ressources" / "qml" / "main.qml"

    engine.load(qml_file)

    if not engine.rootObjects():
        sys.exit(-1)

    sys.exit(app.exec())

and here is my qml file:

import QtQuick.Controls 2.5
import QtQuick.Controls.Material
import QtQml.Models 2.15

Rectangle {
        id: window
        radius: 10
        color : "white"

        border.color: "#546E7A"
        border.width: 2

        property bool expanded : true
        property int ex_height : 125
        width: 400
        height: 140




        Image {
            id: arrow
            source: "../assets/angle-small-up.png"
            height: 15
            fillMode: Image.PreserveAspectFit
            anchors.left: parent.left
            anchors.top: parent.top
            anchors.margins: 5
            MouseArea {
                anchors.fill: parent
                onClicked: {
                    arrow.source = window.expanded ? "../assets/angle-small-down.png" : "../assets/angle-small-up.png"
                    window.expanded = window.expanded ? false : true
                    window.height = window.expanded? window.ex_height : 25
                    seperator01.visible = seperator01.visible ? false: true
                    seperator02.visible = seperator02.visible ? false : true
                    productlist.visible =  productlist.visible ? false : true
                }
            }
        }

        Text {
            id: title
            height: 15
            anchors.left: arrow. right
            anchors.top : parent.top
            anchors.right: parent.right
            anchors.margins : 5
            text: "Product List"
            horizontalAlignment: Text.AlignHCenter
            verticalAlignment: Text.AlignVCenter
        }

        Rectangle {
            id: seperator01
            visible: true
            width : window.width - 10
            height: 1
            color: "#546E7A"
            anchors.top : arrow.bottom
            anchors.left: window.left
            anchors.margins : 5

            Behavior on visible { PropertyAnimation{} }
        }

        Rectangle {
            id: seperator02
            visible: true
            width : window.width - 10
            height: 1
            color: "#546E7A"
            anchors.bottom : parent.bottom
            anchors.left: window.left
            anchors.margins : 5

            Behavior on visible { PropertyAnimation{ duration: 50; easing.type: Easing.OutCubic} }
        }



        ListView {
            id: productlist
            anchors.top: seperator01.bottom
            anchors.left: parent.left
            anchors.right: parent.right
            anchors.bottom: seperator02.top
            model: productListModel
            clip: true
            delegate:         Component{
                id: namedelegate
                Text {
                    text: model.name
                }
            }
        }

}

When I execute the app I get an error for each line of my data: Unable to assign [undefined] to QString.
The last two days I tried to understand the issue and read some of the Qt docs. I also tried to find any answer here in the forum without success.

In the console i can see that the file is read in correctly. I can also debug may.py and see that the engine.rootContext has the Model with correct data.
So i guessed the error might be in the .qml file?!? But googling and reading didn't bring me to a solution.

Can anybody can explain me my mistake?

[jeremy_k]

This is a wild guess, because there is a lot of code for a forum question, but I think the problem is
text: model.name. With Qt 5 and PyQt or PySide, QML doesn't know anything about python (or C++) symbols. I'm presuming this continues to be true with the Qt 6 equivalents. As such, <python object>.<member> isn't usable.

In Models and Views in Qt Quick, the Object Instances as Models and C++ Data Models sections offer a few choices. With an otherwise functional model, implementing QAbstractItemModel::roleNames() is probably the easiest route. data() will need to be updated to use the corresponding role numbers.

[LS-KS]

@jeremy_k

Thank You for the explanation!

As you said I had to implement the roleNames() Function and adjusted the data().

The code below now works

import sys
import typing

import PySide6
from PySide6 import QtCore
from PySide6 import QtGui
from PySide6.QtCore import QByteArray


class ProductListModel (QtCore.QAbstractListModel):

    def __init__(self, products, parent = None):
        super().__init__(parent)
        self.products = products

    def data(self, index, role):
        """Returns an appropriate value for the requested data.
           If the view requests an invalid index, an invalid variant is returned.
           Any valid index that corresponds to a string in the list causes that
          string to be returned."""

        row = index.row()
        if not index.isValid() or row >= len(self.products):
            return None
        product = self.products[row]
        if role == QtCore.Qt.DisplayRole:
            return product.name
        elif role == QtCore.Qt.EditRole:
            return product.name
        elif role == QtCore.Qt.UserRole + 1:
            return product.id
        elif role == QtCore.Qt.UserRole + 2:
            return product.name
        return None

    def headerData(self, section, orientation, role=QtCore.Qt.DisplayRole):
        """Returns the appropriate header string depending on the orientation of
           the header and the section. If anything other than the display role is
           requested, we return an invalid variant."""
        if role != QtCore.Qt.DisplayRole:
            return None
        if orientation == QtCore.Qt.Horizontal:
            return f"Column {section}"
        return f"Row {section}"

    def rowCount(self, parent: typing.Union[PySide6.QtCore.QModelIndex, PySide6.QtCore.QPersistentModelIndex] = ...) -> int:
        # return length of productList
        return len(self.products)

    def roleNames(self):
            roles = {
                QtCore.Qt.UserRole + 1: b'id',
                QtCore.Qt.UserRole + 2: b'name',
            }
            return roles


class Product:
   def __init__(self, id:int, name:str):
       self.id = id
       self.name = name```