python - QMainWindow 中的布局错误？

Question

我在 PyQT5 中遇到错误的布局。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？我将主窗口创建为 QMainWindow，并在其中创建一个小部件作为中央小部件。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，这将定位相对于其父级的位置并生成像您获得的那样的小部件，为了解决这个问题，使用了布局，QMainWindow 是一个特殊的 QWidget，因为它具有预定义的元素，所以它已经有了一个布局:

在 QMainWindow 中，必须使用 setCentralWidget 函数将小部件添加到centralwidget，在您的情况下:

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)

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