使用PyQt5中的菜单栏打开并保存图像文件

Question

I've written the following code to open image file using a menubar in PyQt5. It is able to select the file but not able to display it in the window. I've successfully opened text file but not able to do the same for images. Can you please rectify my error?

import sys
from PyQt5.QtWidgets import QMainWindow, QApplication, QWidget, QLabel, QFileDialog, QAction
from PyQt5.QtGui import QIcon, QPixmap

class MainWindow(QMainWindow):

    def __init__(self, parent = None):
        super(MainWindow, self).__init__(parent)

        menubar = self.menuBar()
        fileMenu = menubar.addMenu('File')
        editMenu = menubar.addMenu('Edit')
        self.resize(500, 500)

        dlg = QFileDialog(self)       
        openAction = QAction('Open Image', self)  
        openAction.triggered.connect(self.openImage) 
        fileMenu.addAction(openAction)

        closeAction = QAction('Exit', self)  
        closeAction.triggered.connect(self.close) 
        fileMenu.addAction(closeAction)



    def openImage(self):
    # This function is called when the user clicks File->Open Image.
        label = QLabel(self)
        filename = QFileDialog.getOpenFileName()
        imagePath = filename[0]
        print(imagePath)
        pixmap = QPixmap(imagePath)
        label.setPixmap(pixmap)
        self.resize(pixmap.width(),pixmap.height())
        self.show()



def main():
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    app.exec_()

if __name__ == '__main__':
    sys.exit(main()) 

Answer 1

When you call show() the widget makes children visible, in your case QLabel is not a child when that method is used, so a trivial but partial solution is to make it visible:

def openImage(self):
    label = QLabel(self)
    label.show()
    # or
    # self.show()

But in the case of QMainWindow is not suitable, QMainWindow is a very special widgets because it has a definite structure as shown in the following image:

As you can see, QLabel is the centralWidget and create it only once, and then you only have to replace the QPixmap if you select a new image:

import sys
from PyQt5.QtWidgets import QMainWindow, QApplication, QLabel, QFileDialog, QAction
from PyQt5.QtGui import QPixmap

class MainWindow(QMainWindow):

    def __init__(self, parent = None):
        super(MainWindow, self).__init__(parent)

        menubar = self.menuBar()
        fileMenu = menubar.addMenu('File')
        editMenu = menubar.addMenu('Edit')
        self.resize(500, 500)

        openAction = QAction('Open Image', self)  
        openAction.triggered.connect(self.openImage) 
        fileMenu.addAction(openAction)

        closeAction = QAction('Exit', self)  
        closeAction.triggered.connect(self.close) 
        fileMenu.addAction(closeAction)
        self.label = QLabel()
        self.setCentralWidget(self.label)

    def openImage(self):
        imagePath, _ = QFileDialog.getOpenFileName()
        pixmap = QPixmap(imagePath)
        self.label.setPixmap(pixmap)
        self.resize(pixmap.size())
        self.adjustSize()

def main():
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    return app.exec_()

if __name__ == '__main__':
    sys.exit(main())