[PySide2 + QML] Error when registering a python class as QML type

NoodlesDev

Hi everyone,

I'm trying to register my Python class as a QML type.
This is the code I'm using:

# This Python file uses the following encoding: utf-8
from enum import Enum

from PySide2.QtMultimedia import QCamera, QCameraImageCapture
from PySide2.QtCore import QObject, QByteArray, Slot, Signal, Property


class CameraMode(Enum):
    """Allowed camera modes.

    Modes represent a set of configurations used in particular scenarios.
    """

    PREVIEW = 0
    CAPTURE = 1


class MyCamera(QObject):
    """Custom  camera controller class

    This class provides a wrapper around a QCamera instance that
    is used as the system camera."""

    cameraReady = Signal()

    def __init__(self):
        """Initialize the MyCamera instance."""

        QObject.__init__(self)

        camera_device = QByteArray(b"/dev/video2")
        self._camera = QCamera(camera_device)
        self._capture = QCameraImageCapture(self._camera)

        self._camera.statusChanged.connect(self._configure)

        self._camera.load()

    @Slot(QCamera.Status)
    def _configure(self, status):

        # Here we configure the camera
        if status == QCamera.LoadedStatus:

            encoding = self._capture.encodingSettings()
            encoding.setCodec("MJPEG")
            self.setMode(CameraMode.PREVIEW)
            self._camera.start()

        elif status == QCamera.ActiveStatus:

            self.cameraReady.emit()

        elif status == QCamera.Error:

            print("ERROR: {}".format(self._camera.errorString))

    def setMode(self, mode):
        """Switch the controlled camera to the desired resolution."""

        if not isinstance(mode, CameraMode):

            raise TypeError("mode should be of type CameraMode")

        if mode == CameraMode.PREVIEW:

            settings = self._camera.viewfinderSettings()
            settings.setResolution(1920, 1080)

        elif mode == CameraMode.CAPTURE:

            raise NotImplementedError

    def provideCamera(self, qml_camera):
        """Provide a new camera to a QDeclarativeCamera instance.

        This function is used to change the QCamera associated to a QML Camera
        in order to provide the configurations that are not allowed by the
        QML type.
        """

        qml_camera.setMediaObject(self._camera)

man.py

# This Python file uses the following encoding: utf-8

# Stdlib imports
import sys
import os.path

# Qt imports
from PySide2.QtWidgets import QApplication
from PySide2.QtQml import QQmlApplicationEngine, qmlRegisterType
from PySide2.QtCore import QUrl

# Our imports
from camera import MyCamera


if __name__ == "__main__":
    app = QApplication([])
    engine = QQmlApplicationEngine()

    # Expose MyCamera to QML
    qmlRegisterType(MyCamera, "Camera", 1, 0, "MyCamera")

    # Finally, we load the QML main file and launch the application
    engine.load(QUrl("qml/main.qml"))

    sys.exit(app.exec_())

Howeven, when the code is run, i get the following error:

QQmlApplicationEngine failed to load component
... main.qml:31 MyCamera is not a type

I really don't see the problem, can anyone please help?

Thanks in advance!

eyllanesc

share main.qml and try changing:

class MyCamera(QObject):
    """Custom  camera controller class

    This class provides a wrapper around a QCamera instance that
    is used as the system camera."""

    cameraReady = Signal()

    def __init__(self, parent=None):
        """Initialize the MyCamera instance."""

        QObject.__init__(self, parent)

NoodlesDev

Hi eyllanesc,

thanks for your reply. I've tried your suggestion but I'm still getting the same error.
Here's my main.qml source code:

import QtQuick 2.14
import QtQuick.Controls 2.14

ApplicationWindow {

    id: root

    title: "QCamera Test"
    visible: true
    visibility: "FullScreen"

    Item {

        id: quit_handler

        focus: true
        Keys.onPressed: {

            // CTRL-Q quits the application
            if (event.key === Qt.Key_Q) {

                event.accepted = true
                Qt.quit()

            }

        }

    }

    MyCamera {

        onCameraReady: {

            content_loader.source = "CameraScreen.qml";
            provideCamera(content_loader.item.camera)

        }

    }

    // Used to dinamically change the application window content
    Loader {

        id: content_loader

        width: parent.width
        height: parent.height

        active: true
        visible: true

        source: "LoadingScreen.qml"

    }

}

eyllanesc

@NoodlesDev You have registered the class "MyCamera" in the module "Camera 1.0" but you have not imported it in the .qml, the solution is:

import QtQuick 2.14
import QtQuick.Controls 2.14

import Camera 1.0

ApplicationWindow {

    // ...

NoodlesDev

Thank you again @eyllanesc ! It worked!

I had already tried doing so, but QtCreator showed an error in the main.qml file saying

 "QML module not found (Camera)"

soo I guessed the import was not necessary! My bad.

The initial error now is gone, but I'm still not managing to make my custom QML type work as expected: when I try to call the provideCamera() method:

   MyCamera {

        onCameraReady: {

            content_loader.source = "CameraScreen.qml";
            provideCamera(content_loader.item.camera)

        }

    }

I get

ReferenceError: provideCamera is not defined

If I change it to:

   MyCamera {

        onCameraReady: {

            content_loader.source = "CameraScreen.qml";
            this.provideCamera(content_loader.item.camera)

        }

    }

I get:

TypeError: Property 'provideCamera' of object MyCamera(0x556bfff82130) is not a function

I'm quite confused...

eyllanesc

@NoodlesDev 1) Qt Creator has many disadvantages with PySide2 compatibility and among them they are not notified of registered types: Qt Quick Designer is not completely PySide2 compatible 2) Only qt-slots are visible from QML.

@Slot(QObject) 
def provideCamera(self, qml_camera):
    # ...

NoodlesDev

@eyllanesc once again, thanks a lot, your suggestion solved the issue.
I guess I trusted Qt Creator too much.