QMainWindow中的布局错误？

Question

我在PyQT5中布局错误。我究竟做错了什么？是否有一些预定义的小字段大小或类似的字段？我将主窗口创建为QMainWindow，并在其中创建了一个窗口小部件作为中央窗口小部件。它是这样的：

class Main(QWidget):
    """The main widget with label and LineEdit"""
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUi()

    def initUi(self):
        """Initialize the UI of the main widget"""
        self.mySourceLabel = QLabel("Select your file:")
        self.mySourceLine = QLineEdit()
        self.mySourceLine.setPlaceholderText("File name here")

        # Set layout
        grid = QGridLayout()
        #grid.setSpacing(5)
        grid.addWidget(self.mySourceLabel, 0, 0)
        grid.addWidget(self.mySourceLine, 1, 0)
        self.setLayout(grid)

class MyApp(QMainWindow):
    """Main application class"""
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUi()

    def initUi(self):
        """Initialize UI of an application"""
        # main window size, title
        self.setGeometry(400, 300, 400, 300)
        self.setWindowTitle("Version upgrade ")

        # create instance of a class Main
        self.main = Main(self)

        # create central widget, create grid layout
        centralWidget = QWidget()
        centralLayout = QGridLayout()
        centralWidget.setLayout(centralLayout)

Answer 1

当您将父级传递给QWidget时，它将相对于其父级定位一个位置，并生成与您所获得的控件类似的控件，以解决此问题，使用了布局，QMainWindow是一种特殊的QWidget，因为它具有预定义的元素，因此它已经具有布局

在QMainWindow中，必须使用setCentralWidget函数将小部件添加到centralwidget：

class MyApp(QMainWindow):
    """Main application class"""
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUi()

    def initUi(self):
        [...]
        centralWidget = Main(self)
        self.setCentralWidget(centralWidget)

完整的代码：

class Main(QWidget):
    """The main widget with label and LineEdit"""
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUi()

    def initUi(self):
        """Initialize the UI of the main widget"""
        self.mySourceLabel = QLabel("Select your file:")
        self.mySourceLine = QLineEdit()
        self.mySourceLine.setPlaceholderText("File name here")

        # Set layout
        grid = QGridLayout()
        #grid.setSpacing(5)
        grid.addWidget(self.mySourceLabel, 0, 0)
        grid.addWidget(self.mySourceLine, 1, 0)
        self.setLayout(grid)

class MyApp(QMainWindow):
    """Main application class"""
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUi()

    def initUi(self):
        """Initialize UI of an application"""
        # main window size, title
        self.setGeometry(400, 300, 400, 300)
        self.setWindowTitle("Version upgrade ")

        # create central widget, create grid layout
        centralWidget = Main(self)
        self.setCentralWidget(centralWidget)