Stuck trying to understand model/view in Python

[Phill]

I'm trying to learn model/view programming in python. There is one key part that I feel I'm stuck on in the minimal code below, the Device class communicates with a physical device over a network connection. At the moment, I'm trying to monitor if the device is recording or not. How should I notify the model of a change in any of the devices?

import sys
from PyQt5 import QtCore, QtWidgets


class Device:
    def __init__(self, name, ip_address):
        self.name = name
        self.ip_address = ip_address
        self.recording = False
        self.connected = False

    def communiction(self):
        # Method to communicate with and obtain recording status
        pass


class DeviceModel(QtCore.QAbstractTableModel):
    def __init__(self, devices):
        super().__init__()
        self.devices = devices

    def columnCount(self, index):
        return 3

    def rowCount(self, index):
        return len(self.devices)

    def headerData(self, section, orientation, role):
        if orientation == QtCore.Qt.Horizontal and role == QtCore.Qt.DisplayRole:
            if section == 0:
                return 'Device'
            if section == 1:
                return 'Recording'
            if section == 2:
                return 'Connected'
        return None

    def data(self, index, role):
        if not index.isValid():
            return
        if role == QtCore.Qt.DisplayRole:
            device = self.devices[index.row()]
            if index.column() == 0:
                return device.name
            if index.column() == 1:
                return device.recording
            if index.column() == 2:
                return device.connected
        else:
            return None


class Main(QtWidgets.QTableView):
    def __init__(self):
        super().__init__()
        self.devices = [Device('Device 1', 'x.x.x.x'),
                        Device('Device 2', 'x.x.x.x'),
                        Device('Device 3', 'x.x.x.x')]
        self.device_model = DeviceModel(self.devices)
        self.setModel(self.device_model)


def main():
    app = QtWidgets.QApplication(sys.argv)
    form = Main()
    form.show()
    app.exec()

if __name__ == '__main__':
    main()

[SGaist]

Hi,

Basically it's the same way as C++ as described here.

[Phill]

@SGaist Thanks for your reply, but I can only find information about changing the data through the model on that page.

The page does state:
"The data itself does not have to be stored in the model; it can be held in a data structure or repository provided by a separate class, a file, a database, or some other application component."

But does not allude to a way for the data structure to let the model know that it has changed. For example if "Device 1" communicates that recording has stopped how would I inform the model that the recording attribute has changed?

[kshegunov]

@Phill said in Stuck trying to understand model/view in Python:

But does not allude to a way for the data structure to let the model know that it has changed. For example if "Device 1" communicates that recording has stopped how would I inform the model that the recording attribute has changed?

That is because it's entirely up to you. The model is just a interface (a facade) for the data. You must ensure that it emits the appropriate signals so it notifies the view, and if your model's data can be edited from the view, then it must also implement QAbstractItemModel::setData and friends, but there are no real requirements on how the model will bookkeep the dataset (if at all).

One possibility is that your device is represented by a QObject and emits signals which are connected to slots in your model.