PyQt5问题：用QtDesigner创建的QMainWindow为何无法正常显示？

问题 #

我尝试用QtDesigner制作一个简单的Hello World界面，通过pyuic5导出为qthelloworld.py，代码如下：

# Form implementation generated from reading ui file '.\qtdesigner_test.ui'
#
# Created by: PyQt5 UI code generator 5.15.9
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.horizontalLayoutWidget = QtWidgets.QWidget(self.centralwidget)
        self.horizontalLayoutWidget.setGeometry(QtCore.QRect(9, 9, 771, 551))
        self.horizontalLayoutWidget.setObjectName("horizontalLayoutWidget")
        self.horizontalLayout = QtWidgets.QHBoxLayout(self.horizontalLayoutWidget)
        self.horizontalLayout.setContentsMargins(0, 0, 0, 0)
        self.horizontalLayout.setObjectName("horizontalLayout")
        self.pushButton = QtWidgets.QPushButton(self.horizontalLayoutWidget)
        self.pushButton.setObjectName("pushButton")
        self.horizontalLayout.addWidget(self.pushButton)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName("menubar")
        self.menuI_have_typed_here = QtWidgets.QMenu(self.menubar)
        self.menuI_have_typed_here.setObjectName("menuI_have_typed_here")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.menubar.addAction(self.menuI_have_typed_here.menuAction())

        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", "Hello World!"))
        self.menuI_have_typed_here.setTitle(_translate("MainWindow", "I have typed here"))

随后编写了运行脚本：

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QApplication
import sys
from qthelloworld import Ui_MainWindow

class Window(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setupUi(self)

def main():
    app = QApplication(sys.argv)
    win = Window()
    win.show()
    app.exec()

if __name__ == '__main__':
    main()

此前手动创建过相同结构的PyQt5程序，运行正常，但此次用QtDesigner生成的窗口仅短暂闪烁后就关闭了。请问哪里操作出错了？

解决方案 #

问题出在运行脚本的事件循环调用上。在PyQt5中，exec是Python的关键字，因此PyQt5将事件循环方法命名为exec_()（带下划线），而非exec()。

你当前调用的app.exec()并没有正确启动Qt的事件循环，程序执行到此处后直接退出，导致窗口一闪而过。

修改运行脚本中的main函数，将app.exec()替换为app.exec_()即可：

def main():
    app = QApplication(sys.argv)
    win = Window()
    win.show()
    app.exec_()  # 替换为exec_()

此外，也可以使用sys.exit(app.exec_())确保程序退出时正确清理资源，写法如下：

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

修改完成后，窗口就能正常显示并保持打开状态。

内容的提问来源于stack exchange，提问作者Joonas Joensuu