How to set currentIndex in ComboBox

Fabian Sturm

Hi,
I have a hard time understanding the concept of the ComboBox. I can set the model to a custom QQmListProperty and setting the textRole. And I also can set the currentIndex to e.g. a number to select the right element. But what I really want is the ComboBox to automatically calculate it's index through a short Javascript function. This function e.g. searches through the model until it finds a match.
This works as long as the model does not change. After I append a new item to the model, the new list is loaded but the currentIndex is reset to 0. How would I also make it reload the new index? Thanks for any help I really appreciate it!

Appended is my implementation with PyQt but I doubt this matters from a pure C++ implementation.

main.qml

import QtQuick 2.2
import QtQuick.Layouts 1.1
import QtQuick.Controls 1.2
import QtQuick.Dialogs 1.2
import MyModel 1.0
import MyItem 1.0

ApplicationWindow {

    function getCurrentIndex(list, element) {
        if (list && element) {
            for (var i = 0; i < list.length; i++) {
                if (list[i].name === element.name) {
                    console.log('Found item at pos: ' + i)
                    return i
                }
            }
        }
        return -1
    }

    id: mainWindow
    width: 800; height: 600
    color: "gray"

    MyModel {
      id: mymodel
    }

    ComboBox {
        id: combo
        width: parent.width
        currentIndex: getCurrentIndex(mymodel.items, mymodel.item)
        model: mymodel.items
        textRole: 'name'
    }
    Button {
        anchors.top: combo.bottom
        text: 'Add item'
        onClicked: mymodel.new_item()
    }

}

mymodel.py

from PyQt5.QtCore import pyqtProperty, pyqtSignal, pyqtSlot, QObject
from PyQt5.QtQml import QQmlListProperty


class MyItem(QObject):

    nameChanged = pyqtSignal()

    def __init__(self, name, parent=None):
        QObject.__init__(self, parent)
        self._name = name

    @pyqtProperty('QString', notify=nameChanged)
    def name(self):
        return self._name


class MyModel(QObject):

    itemChanged = pyqtSignal()
    itemsChanged = pyqtSignal()

    def __init__(self, parent=None):
        QObject.__init__(self, parent)
        self._items = [MyItem('one'), MyItem('two'), MyItem('three')]
        self._item = self._items[1]

    @pyqtProperty(MyItem, notify=itemChanged)
    def item(self):
        return self._item

    @pyqtProperty(QQmlListProperty, notify=itemsChanged)
    def items(self):
        print('Query for items')
        return QQmlListProperty(MyItem, self, self._items)

    @pyqtSlot()
    def new_item(self):
        print('Append new item')
        self._items.append(MyItem('new'))
        self.itemsChanged.emit()

main.py

import os
import sys

from PyQt5 import QtCore, QtQml, QtWidgets
from mymodel import MyModel, MyItem

osname = os.name.lower()
sysplatform = sys.platform.lower()
windows = os.name.lower() == "nt" and sysplatform.startswith("win")

# PyQt class name, QML URI, major version, minor version, QML type name
QtQml.qmlRegisterType(MyModel, 'MyModel', 1, 0, 'MyModel')
QtQml.qmlRegisterType(MyItem, 'MyItem', 1, 0, 'MyItem')

app = QtWidgets.QApplication(sys.argv)

# Create the QML engine
engine = QtQml.QQmlEngine(app)
engine.quit.connect(app.quit)

# Load the main.qml file and create the toplevel component
component = QtQml.QQmlComponent(engine)
currentFilePath = os.path.dirname(os.path.abspath(__file__))
mainFilepath = os.path.join(currentFilePath, "main.qml")
if windows:
    mainFilepath = mainFilepath.replace('\\', '/')
qmlFile = QtCore.QUrl("file:///" + mainFilepath)
component.loadUrl(qmlFile)
if component.status() != QtQml.QQmlComponent.Ready:
    for error in component.errors():
        print(error.toString())
    sys.exit(-1)

topLevelItem = component.create()
if not topLevelItem:
    for error in component.errors():
        print(error.toString())
    sys.exit(-1)

# Now run the main loop until the user closes the application
topLevelItem.show()
sys.exit(app.exec_())