How to link QGraphicsScene to QGraphicsView inside a QtDesigner generated code

Question

I want to display an image using QGraphicsView in a window. I have a basic QGraphicsView and a button based test.ui file generated from QtDesigner tool. Corresponding test.py file:

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'test.ui'
#
# Created by: PyQt5 UI code generator 5.9.2
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(640, 480)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.graphicsView = QtWidgets.QGraphicsView(self.centralwidget)
        self.graphicsView.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.graphicsView.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.graphicsView.setObjectName("graphicsView")
        self.verticalLayout.addWidget(self.graphicsView)
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setObjectName("pushButton")
        self.verticalLayout.addWidget(self.pushButton)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 640, 26))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))


if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

I made use of QGraphicsScene to display an image inside this QGraphicsView. My current working solution is to mess up the above .py file as follows:

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'test.ui'
#
# Created by: PyQt5 UI code generator 5.9.2
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(640, 480)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.scene = QtWidgets.QGraphicsScene(self.centralwidget) #added 
        self.graphicsView = QtWidgets.QGraphicsView(self.scene) #edited
        self.graphicsView.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.graphicsView.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOn)
        self.graphicsView.setObjectName("graphicsView")
        self.verticalLayout.addWidget(self.graphicsView)
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setObjectName("pushButton")
        self.verticalLayout.addWidget(self.pushButton)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 640, 26))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))
        
        self.pushButton.clicked.connect(self.display)
        
    
    def display(self):
        import imageio, numpy
        self.scene.clear()
        input_image = imageio.imread('image.jpg').copy()
        height, width, channels = input_image.shape
        bytesPerLine = channels * width        
        qimg = QtGui.QImage(input_image, width, height, bytesPerLine, QtGui.QImage.Format_RGB888)
        self.pixmap = QtGui.QPixmap.fromImage(qimg)        
        self.scene.addPixmap(self.pixmap) #add pixmap to scene
        self.graphicsView.scale(0.5,0.5) 
        self.scene.update()
             
               

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

However, this solution is not systematic. I want to do the same without editing the original test.ui generated test.py file.

So, I tried following code which to me appears like a systematic translation of the previous working code. However, it fails to produce any display on button click:

from PyQt5 import QtCore, QtGui, QtWidgets
from test import Ui_MainWindow


class myWindow(QtWidgets.QMainWindow, Ui_MainWindow): 
    def __init__(self, parent=None): 
        QtWidgets.QMainWindow.__init__(self, parent=parent) 
        self.setupUi(self)
        
        self.scene = QtWidgets.QGraphicsScene(self.centralwidget) #append scene method
        self.graphicsView = QtWidgets.QGraphicsView(self.scene) #graphicsView re-assigned with scene           
       
        self.pushButton.clicked.connect(self.display)    


        
    def display(self):
        import imageio, numpy
        self.scene.clear()
        input_image = imageio.imread('image.jpg').copy()
        height, width, channels = input_image.shape
        bytesPerLine = channels * width        
        qimg = QtGui.QImage(input_image, width, height, bytesPerLine, QtGui.QImage.Format_RGB888)
        self.pixmap = QtGui.QPixmap.fromImage(qimg)        
        self.scene.addPixmap(self.pixmap) #add pixmap to scene
        self.graphicsView.scale(0.5,0.5) 
        self.scene.update()       
    

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = myWindow()
    w.show()
    sys.exit(app.exec_())

I am likely messing up something due to my limited understanding of class inheritance, QGraphicsView, and QGraphicsScene. Any pointers to my mistakes would be very helpful.

Note: I am using a myWindow class to integrate some key press functionality in future. I think the issue is more to do with how to selectively append/redefine few lines inside a parent class function. Is this even possible without re-writing the whole setupUi method? Or, is there another smarter way to perform the same task?

Answer 1

You have to set the scene to the existing QGraphicsView instead of creating a new QGraphicsView:

class myWindow(QtWidgets.QMainWindow, Ui_MainWindow): 
    def __init__(self, parent=None): 
        QtWidgets.QMainWindow.__init__(self, parent) 
        self.setupUi(self)
        
        self.scene = QtWidgets.QGraphicsScene(self.centralwidget)
        self.graphicsView.setScene(self.scene)
        self.pushButton.clicked.connect(self.display)

    def display(self):
        # ...