QLayout的设置对齐（QWidget，对齐）、设置对齐（QLayout，对齐）和设置对齐（对齐）之间有什么区别？（PyQt5）

Question

在以下代码中：

import sys

from PyQt5           import QtWidgets
from PyQt5.QtCore    import Qt
from PyQt5.QtWidgets import QApplication, QWidget, QHBoxLayout, QTableWidget, QPushButton

class Window(QtWidgets.QMainWindow):
    def __init__(self, method):
        super(Window, self).__init__()

        mainWidget = QWidget()
        mainLayout = QHBoxLayout(mainWidget)

        table = QTableWidget(10, 3)
        button1 = QPushButton("Play")
        button2 = QPushButton("Cancel")

        mainLayout.addWidget(table)
        mainLayout.addWidget(button1)
        mainLayout.addWidget(button2)

        if   (method == 1):
            rtnValue = mainLayout.setAlignment(button1, Qt.AlignTop)
            print("Method 1:", rtnValue)
        elif (method == 2):
            rtnValue = mainLayout.setAlignment(mainLayout, Qt.AlignTop)
            print("Method 2:", rtnValue)
        else:
            rtnValue = mainLayout.setAlignment(Qt.AlignTop)
            print("Method X:", rtnValue)

        self.setCentralWidget(mainWidget)
        self.show()

if __name__ == "__main__":
    print("python QLayoutAlignment.py[ <MethodToUse=1>")
    app = QApplication(sys.argv)
    method = 1 if (len(sys.argv) < 2) else int(sys.argv[1])
    GUI = Window(method)
    sys.exit(app.exec_())

当我在调用mainLayout.setAlignment(button1, Qt.AlignTop)的情况下调用下面这样的程序时，它会像预期的那样工作，“播放”按钮在顶部对齐，“取消”按钮在垂直中心对齐。我还在Qt中找到了bool QLayout::setAlignment(QWidget *w, Qt::Alignment alignment)的文档

python QLayoutAlignment.py 1

然而，当我像下面那样调用程序，调用mainLayout.setAlignment(mainLayout, Qt.AlignTop)时，它似乎不起作用。所有按钮都垂直居中对齐。我将bool QLayout::setAlignment(QLayout *l, Qt::Alignment alignment)的Qt文档解释为“它将所有添加的布局小部件与集合对齐对齐”。那么这个函数实际上做什么（何时使用）

python QLayoutAlignment.py 2

最后，我还看到了来自Center and top align a QVBoxLayout的另一个例子。当我在调用mainLayout.setAlignment(Qt.AlignTop)的情况下调用下面这样的程序时，它也不会在所有按钮垂直居中对齐的情况下工作。对于这一个，我找不到它的文档。那么这个函数实际上做什么（何时使用）以及在哪里可以找到它的文档

python QLayoutAlignment.py 3

Answer 1

接受布局的.setAlignment方法用于对齐子布局，即使用.addLayout添加到父布局的子布局

下面是一个基于您的代码的小演示

import sys

from PyQt5           import QtWidgets
from PyQt5.QtCore    import Qt
from PyQt5.QtWidgets import QApplication, QWidget, QHBoxLayout, QTableWidget, QPushButton

class Window(QtWidgets.QMainWindow):
    def __init__(self, method=0):
        super(Window, self).__init__()

        mainWidget = QWidget()
        self.mainLayout = QHBoxLayout(mainWidget)

        table = QTableWidget(10, 3)
        self.button1 = QPushButton("Play")
        self.button2 = QPushButton("Cancel")

        self.subLayout = QHBoxLayout()
        buttona1 = QPushButton("1")
        buttona1.clicked.connect(self.clicked1)
        buttona2 = QPushButton("2")
        buttona2.clicked.connect(self.clicked2)
        buttona3 = QPushButton("3")
        buttona3.clicked.connect(self.clicked3)
        buttona4 = QPushButton("4")
        buttona4.clicked.connect(self.clicked4)
        self.subLayout.addWidget(buttona1)
        self.subLayout.addWidget(buttona2)
        self.subLayout.addWidget(buttona3)
        self.subLayout.addWidget(buttona4)

        self.mainLayout.addWidget(table)
        self.mainLayout.addWidget(self.button1)
        self.mainLayout.addWidget(self.button2)
        self.mainLayout.addLayout(self.subLayout)

        self.setCentralWidget(mainWidget)
        self.show()

    def clicked1(self):
        rtnValue = self.mainLayout.setAlignment(self.button1, Qt.AlignTop)
        print("Method 1:", rtnValue)

    def clicked2(self):
        rtnValue = self.mainLayout.setAlignment(self.mainLayout, Qt.AlignTop)
        print("Method 2:", rtnValue)

    def clicked3(self):
        rtnValue = self.mainLayout.setAlignment(Qt.AlignTop)
        print("Method 3:", rtnValue)

    def clicked4(self):
        rtnValue = self.mainLayout.setAlignment(self.subLayout, Qt.AlignTop)
        print("Method 4:", rtnValue)


if __name__ == "__main__":
    print("python QLayoutAlignment.py[ <MethodToUse=1>")
    app = QApplication(sys.argv)
    method = 1 if (len(sys.argv) < 2) else int(sys.argv[1])
    GUI = Window(method)
    sys.exit(app.exec_())

您会注意到，如果触发此self.mainLayout.setAlignment(self.mainLayout, Qt.AlignTop)，返回值为False。此is telling you表明在当前布局中找不到正在对齐的布局。由于您正在mainLayout上调用.setAlignment，因此您影响的布局必须在该布局中

在第4个方法中，我添加了一个子布局，正如您所看到的（rtnValue = self.mainLayout.setAlignment(self.subLayout, Qt.AlignTop)）按预期工作并返回True