如何将复选框与 PyQT5 中的按钮对齐？

Question

from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys

class Window(QWidget):
    def __init__(self):
        super().__init__()
        self.mainLayout = QFormLayout()
        check_box = QCheckBox()
        my_button = QPushButton("My button")
        my_button.setFont(QFont("Roboto", 18))
        self.mainLayout.addRow(check_box, my_button)
        self.setLayout(self.mainLayout)


app = QApplication(sys.argv)
mainWindow = Window()
mainWindow.show()
sys.exit(app.exec_())

The check box is not in line with the button. How can I line them up? They both need to be a row on a QFormLayout.

Answer 1

When setting a widget as a "label" for QFormLayout, the alignment follows the default behavior, which is to align the widget on the top left (while taking into account the size policy).

The labelAlignment property won't help here, as it only considers the horizontal alignment.

Trying to manually set the alignment of the layout item used for the "label" widget is not enough, as QFormLayout sets geometries programmatically, and "labels" are always top aligned.

To vertically center the widget, there are two possibilities:

Set an expanding vertical size policy

By default, QCheckBox has a Fixed vertical sizePolicy , meaning that it will always have the same height and therefore will be top aligned due to the default behavior of QFormLayout.

You can change the vertical policy of the widget, and it will then be vertically centered:

    check_box = QCheckBox()
    check_box.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Expanding)

Important : this will only work for widgets with controls that have a specific height, like QCheckBox or QRadioButton. Setting an expanding vertical policy for "resizable" widgets (like QComboBox) will make that widget occupy the whole available height. To avoid that, use the following solution.

Create a container

A more appropriate solution is to create a container for the actual widget, specify an expanding vertical size policy for that container, set a basic box layout and add the checkbox.

Basic layouts (QGridLayout, QBoxLayout) always try to make their widgets occupy all the available space in their layout "slot", and if the widget has a fixed size policy then it will be centered in the available rectangle.

    check_box = QCheckBox()
    check_container = QWidget()
    check_container.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Expanding)
    check_layout = QVBoxLayout(check_container)
    check_layout.setContentsMargins(0, 0, 0, 0) # Important!
    check_layout.addWidget(check_box)
    my_button = QPushButton("My button")
    my_button.setFont(QFont("Roboto", 18))
    self.mainLayout.addRow(check_container, my_button)