[FIXED] Qt and opencv app not working in virtual environment

Issue

I created a GUI app using pyqt5 and opencv. The app works fine without activating the virtual env but when I activate the virtual env and run the app it shows this error:

QObject::moveToThread: Current thread (0x125b2f0) is not the object's thread (0x189e780).
Cannot move to target thread (0x125b2f0)

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/home/deepak/Desktop/SampleApp/lib/python3.9/site-packages/cv2/qt/plugins" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: xcb, eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, webgl.

Aborted

I tried running an example pyqt5 code (without importing opencv) and another code (only using opencv) both worked fine in the virtual env.

Operating System: Parrot OS 4.11

Python Version: 3.9.2

Solution

The problem is that the version of Qt with which opencv was compiled is not similar to the one used by PyQt5 causing a conflict.

A possible solution is to indicate to use the Qt plugins used by PyQt5.

import os
from pathlib import Path

import PyQt5
from PyQt5.QtWidgets import QWidget # others imports
import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = os.fspath(
    Path(PyQt5.__file__).resolve().parent / "Qt5" / "plugins"
)
# ...

For PySide2:

import os
from pathlib import Path

import PySide2
from PySide2.QtWidgets import QWidget # others imports
import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = os.fspath(
    Path(PySide2.__file__).resolve().parent / "Qt" / "plugins"
)
# ...

Update:

A better option is to use QLibraryInfo to get the plugins folder path:

import os

from PyQt5.QtCore import QLibraryInfo
# from PySide2.QtCore import QLibraryInfo

import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = QLibraryInfo.location(
    QLibraryInfo.PluginsPath
)

Answered By - eyllanesc