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Question

我使用 Qt Designer 设计了一个 GUI，并使用 PyQt5 中的命令将 .ui 文件转换为 .py。由此，我想在单击按钮时输出一个消息框。我已经在按钮监听器的功能上使用这行代码成功地完成了它：

QtWidgets.QMessageBox.about(MainWindow, "Result", "Invalid number entered!")

我在互联网上搜索过，但我不明白为什么这个不起作用。

QtWidgets.QMessageBox.about(self, "Result", "Invalid number entered!")

self 是否也指 MainWindow？

这里是完整的源代码。

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.setWindowModality(QtCore.Qt.WindowModal)
        #MainWindow.resize(310, 185)
        MainWindow.setFixedSize(310, 185)
        MainWindow.setStyleSheet("#MainWindow\n"
    "{\n"
    "    background-color:qradialgradient(spread:pad, cx:0.5, cy:0.5, 
    radius:1.696, fx:0.5, fy:0.505682, stop:0 rgba(0, 85, 255, 255), stop:1 
    rgba(255, 255, 255, 255))\n"
    "}\n"
    "\n"
    "#firstNo_lineedit, #secondNo_lineedit\n"
    "{\n"
    "    \n"
    "    background-color: rgb(28, 255, 123);\n"
    "}\n"
    "\n"
    "")
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.firstNo_lineedit = QtWidgets.QLineEdit(self.centralwidget)
        self.firstNo_lineedit.setGeometry(QtCore.QRect(130, 40, 113, 20))
        self.firstNo_lineedit.setObjectName("firstNo_lineedit")
        self.secondNo_lineedit = QtWidgets.QLineEdit(self.centralwidget)
        self.secondNo_lineedit.setGeometry(QtCore.QRect(130, 70, 113, 20))
        self.secondNo_lineedit.setObjectName("secondNo_lineedit")
        self.calculate_button = QtWidgets.QPushButton(self.centralwidget)
        self.calculate_button.setGeometry(QtCore.QRect(170, 100, 75, 23))
        self.calculate_button.setObjectName("calculate_button")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(60, 40, 81, 20))
        self.label.setObjectName("label")
        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(60, 70, 61, 20))
        self.label_2.setObjectName("label_2")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 310, 21))
        self.menubar.setObjectName("menubar")
        self.menuAbout = QtWidgets.QMenu(self.menubar)
        self.menuAbout.setObjectName("menuAbout")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.menubar.addAction(self.menuAbout.menuAction())

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

        # ================= Listeners ===================
        self.calculate_button.clicked.connect(self.basicArithmetic)
        # ============================================

    # ================= Events ===================
    def basicArithmetic(self):
        try:
            firstNo=float(self.firstNo_lineedit.text())
            secondNo=float(self.secondNo_lineedit.text())

            resSum=firstNo+secondNo
            resDiff=firstNo-secondNo
            resMul=firstNo*secondNo
            resDiv=round(firstNo/secondNo,2)

            print("Sum: {}".format(resSum))
            print("Difference: {}".format(resDiff))
            print("Product: {}".format(resMul))
            print("Quotient: {}".format(resDiv))

            toDisplay="Sum: {}".format(resSum)
            toDisplay+="\n"
            toDisplay+="Difference: {}".format(resDiff)
            toDisplay+="\n"
            toDisplay+="Product: {}".format(resMul)
            toDisplay+="\n"
            toDisplay+="Quotient: {}".format(resDiv)

            #QtWidgets.QMessageBox.about(self, "Result", toDisplay)
            QtWidgets.QMessageBox.about(MainWindow, "Result", toDisplay)

        except ValueError:
            #QtWidgets.QMessageBox.about(self, "Result", toDisplay)
            QtWidgets.QMessageBox.about(MainWindow, "Result", "Invalid number entered!")
    # ============================================

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.calculate_button.setText(_translate("MainWindow", "Calculate"))
        self.label.setText(_translate("MainWindow", "First No.:"))
        self.label_2.setText(_translate("MainWindow", "Second No.:"))
        self.menuAbout.setTitle(_translate("MainWindow", "About"))
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_())

Answer 1

self 是引用相同实例的类的方法的第一个参数（名称是约定俗成的，不是强制性的）。

对于另一个QMessageBox.about() 需要一个从QWidget 或None 继承的某种对象作为第一个参数。

如果我们查看 Qt Designer 生成的类，我们清楚地看到它不是一个小部件，实际上该类的唯一目的是作为一个接口来填充另一个小部件：

MainWindow = QtWidgets.QMainWindow() # create widget
ui = Ui_MainWindow() # create interface
ui.setupUi(MainWindow) # fill widget

因此，您要传递的self，Ui_MainWindow 的实例是不合适的，因为它不引用小部件，但MainWindow 是一个小部件，因此它可以在该更改下正常工作。 同样在生成的文件中，您会看到以下消息：

# WARNING! All changes made in this file will be lost!

该消息是因为如果您想更改设计，您将不得不覆盖您编写的逻辑，例如您的 basicArithmetic 方法，这会使项目无法维持。

PyQt 我建议创建另一个使用生成 QtDesigner 的类的类，我假设生成的文件名为 design.py

design.py：

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

# Form implementation generated from reading ui file 'design.ui'
#
# Created by: PyQt5 UI code generator 5.10.1
#
# 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.setWindowModality(QtCore.Qt.WindowModal)
        #MainWindow.resize(310, 185)
        MainWindow.setFixedSize(310, 185)
        MainWindow.setStyleSheet("#MainWindow\n"
    "{\n"
    "    background-color:qradialgradient(spread:pad, cx:0.5, cy:0.5," 
    "radius:1.696, fx:0.5, fy:0.505682, stop:0 rgba(0, 85, 255, 255), stop:1" 
    "rgba(255, 255, 255, 255))\n"
    "}\n"
    "\n"
    "#firstNo_lineedit, #secondNo_lineedit\n"
    "{\n"
    "    \n"
    "    background-color: rgb(28, 255, 123);\n"
    "}\n"
    "\n"
    "")
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.firstNo_lineedit = QtWidgets.QLineEdit(self.centralwidget)
        self.firstNo_lineedit.setGeometry(QtCore.QRect(130, 40, 113, 20))
        self.firstNo_lineedit.setObjectName("firstNo_lineedit")
        self.secondNo_lineedit = QtWidgets.QLineEdit(self.centralwidget)
        self.secondNo_lineedit.setGeometry(QtCore.QRect(130, 70, 113, 20))
        self.secondNo_lineedit.setObjectName("secondNo_lineedit")
        self.calculate_button = QtWidgets.QPushButton(self.centralwidget)
        self.calculate_button.setGeometry(QtCore.QRect(170, 100, 75, 23))
        self.calculate_button.setObjectName("calculate_button")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(60, 40, 81, 20))
        self.label.setObjectName("label")
        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(60, 70, 61, 20))
        self.label_2.setObjectName("label_2")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 310, 21))
        self.menubar.setObjectName("menubar")
        self.menuAbout = QtWidgets.QMenu(self.menubar)
        self.menuAbout.setObjectName("menuAbout")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        self.menubar.addAction(self.menuAbout.menuAction())

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.calculate_button.setText(_translate("MainWindow", "Calculate"))
        self.label.setText(_translate("MainWindow", "First No.:"))
        self.label_2.setText(_translate("MainWindow", "Second No.:"))
        self.menuAbout.setTitle(_translate("MainWindow", "About"))

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_())

这个新类可以有以下形式：

ma​​in.py:

from PyQt5 import QtCore, QtGui, QtWidgets

from design import Ui_MainWindow

class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, *args, **kwargs):
        QtWidgets.QMainWindow.__init__(self, *args, **kwargs)
        self.setupUi(self)  

        # ================= Listeners ===================
        self.calculate_button.clicked.connect(self.basicArithmetic)
        # ============================================

    # ================= Events ===================
    def basicArithmetic(self):
        try:
            firstNo=float(self.firstNo_lineedit.text())
            secondNo=float(self.secondNo_lineedit.text())

            resSum=firstNo+secondNo
            resDiff=firstNo-secondNo
            resMul=firstNo*secondNo
            resDiv=round(firstNo/secondNo,2)

            print("Sum: {}".format(resSum))
            print("Difference: {}".format(resDiff))
            print("Product: {}".format(resMul))
            print("Quotient: {}".format(resDiv))

            toDisplay="Sum: {}".format(resSum)
            toDisplay+="\n"
            toDisplay+="Difference: {}".format(resDiff)
            toDisplay+="\n"
            toDisplay+="Product: {}".format(resMul)
            toDisplay+="\n"
            toDisplay+="Quotient: {}".format(resDiv)

            #QtWidgets.QMessageBox.about(self, "Result", toDisplay)
            QtWidgets.QMessageBox.about(self, "Result", toDisplay)

        except ValueError:
            #QtWidgets.QMessageBox.about(self, "Result", toDisplay)
            QtWidgets.QMessageBox.about(self, "Result", "Invalid number entered!")

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

这就是为什么在许多情况下，self 被视为第一个参数。

您可以在以下链接中找到更多信息：

• http://pyqt.sourceforge.net/Docs/PyQt5/designer.html

Answer 2

没有自我指的是Ui_MainWindowclass，其中MainWindow指的是QtWidgets.QMainWindow() 因此，当您说QtWidgets.QMessageBox.about(self, "Result", toDisplay) 时，它会将Ui_MainWindow 视为父母QWidget，这是不正确的。

这次当您调用QtWidgets.QMessageBox.about(MainWindow, "Result", toDisplay) 时，您的代码将运行良好，因为MainWindow 是有效的QWidget，即QtWidgets.QMainWindow()

希望这会有所帮助。