setAlignment(QtCore.Qt.AlignCenter) method is not working as expected

by Martin Fitzpatrick Last updated 13 September 2023 FAQ

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bentraje6381 | 2020-11-29 05:33:05 UTC | #1

Hi,

I'm trying to center a log-in form relative to window space but the setAlignment(QtCore.Qt.AlignCenter) is not working as expected.

You can check the code below so far:

python

import sys
import os
import json

import PySide2
from PySide2 import QtCore
from PySide2.QtCore import Qt, QTimer
from PySide2.QtWidgets import QApplication, QMainWindow, QSpinBox, QWidget, QPushButton, QTextEdit, QVBoxLayout, QHBoxLayout, QLineEdit, QLabel, QStackedLayout
from PySide2 import QtWidgets


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()

        self.setWindowTitle("Quiz Application")

        self.setFixedWidth(500)
        self.setFixedHeight(500)

        # LOG IN LAYOUT

        self.login_layout =  QVBoxLayout()

        login_form_layout = QtWidgets.QFormLayout()
        self.username_edit = QtWidgets.QLineEdit()
        self.password_edit = QtWidgets.QLineEdit()
        self.username_edit.setFixedWidth(120)
        self.password_edit.setFixedWidth(120)
        login_form_layout.addRow(QtWidgets.QLabel("Username"), self.username_edit)
        login_form_layout.addRow(QtWidgets.QLabel("Password"), self.password_edit)


        self.login_btn = QPushButton("Log In")
        self.login_btn.setFixedWidth(120)
        self.login_btn.pressed.connect(self.login_cmd)
        login_form_layout.addWidget(self.login_btn)

        self.login_layout.addLayout(login_form_layout)
        self.login_layout.addStretch()

        self.login_widget = QWidget()
        self.login_widget.setLayout(self.login_layout)


        # Main Menu Layout

        self.main_menu_layout =  QVBoxLayout()
        self.logout_btn = QPushButton("Log Out")
        self.logout_btn.setFixedWidth(120)
        self.logout_btn.pressed.connect(self.logout_cmd)
        self.main_menu_layout.addWidget(self.logout_btn)
        self.main_menu_layout.addStretch()

        self.main_menu_widget = QWidget()
        self.main_menu_widget.setLayout(self.main_menu_layout )

        # Stack Layout
        self.stack_layout = QStackedLayout()
        self.stack_layout.addWidget(self.login_widget)
        self.stack_layout.addWidget(self.main_menu_widget)
        self.stack_layout.setCurrentIndex(0)
        self.stack_layout.setAlignment(QtCore.Qt.AlignCenter)


        widget = QWidget()
        widget.setLayout(self.stack_layout)
        self.setCentralWidget(widget)

    def login_cmd(self):
        self.stack_layout.setCurrentIndex(1)

    def logout_cmd(self):
        self.stack_layout.setCurrentIndex(0)


app = QApplication(sys.argv)

window = MainWindow()
window.show()
app.exec_()

py005_pyqt_center_layout_in_the window|690x403

Salem_Bream | 2020-12-01 14:14:54 UTC | #2

@bentraje6381

There are several issues we need to address.

You are adding stretches! .addStrech(), stretches will try to eat most of the layout available space and forces the widgets inside the layout to be shrunk. Just delete the .addStretch() statements.
you are setting the alignment of the QStackedLayout which shows only 1 widget at any given time!, so its alignment is meaningless. You need to set the alignment for the layouts of widgets themselves inside it.
the QFormLayout is a special case, not as other layouts, it has special option to specify the layout, read the documentation to know more. Use form_layout_xx.setFormAlignment().

Here is a working code...

python

import sys
import os
import json

import PySide2
from PySide2 import QtCore
from PySide2.QtCore import Qt, QTimer
from PySide2.QtWidgets import QApplication, QMainWindow, QSpinBox, QWidget, QPushButton, QTextEdit, QVBoxLayout, QHBoxLayout, QLineEdit, QLabel, QStackedLayout
from PySide2 import QtWidgets


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()

        self.setWindowTitle("Quiz Application")

        self.setFixedWidth(500)
        self.setFixedHeight(500)

        # LOG IN LAYOUT

        self.login_layout = QVBoxLayout()

        login_form_layout = QtWidgets.QFormLayout()

        self.username_edit = QtWidgets.QLineEdit()
        self.password_edit = QtWidgets.QLineEdit()
        self.username_edit.setFixedWidth(120)
        self.password_edit.setFixedWidth(120)
        login_form_layout.addRow(QtWidgets.QLabel(
            "Username"), self.username_edit)
        login_form_layout.addRow(QtWidgets.QLabel(
            "Password"), self.password_edit)

        self.login_btn = QPushButton("Log In")
        self.login_btn.setFixedWidth(120)
        self.login_btn.pressed.connect(self.login_cmd)
        login_form_layout.addWidget(self.login_btn)

        self.login_layout.addLayout(login_form_layout)
        login_form_layout.setFormAlignment(Qt.AlignCenter)

        self.login_widget = QWidget()
        self.login_widget.setLayout(self.login_layout)

        # Main Menu Layout

        self.main_menu_layout = QVBoxLayout()
        self.logout_btn = QPushButton("Log Out")
        self.logout_btn.setFixedWidth(120)
        self.logout_btn.pressed.connect(self.logout_cmd)
        self.main_menu_layout.addWidget(self.logout_btn)
        self.main_menu_layout.setAlignment(QtCore.Qt.AlignCenter)

        self.main_menu_widget = QWidget()
        self.main_menu_widget.setLayout(self.main_menu_layout)

        # Stack Layout
        self.stack_layout = QStackedLayout()
        self.stack_layout.addWidget(self.login_widget)
        self.stack_layout.addWidget(self.main_menu_widget)
        self.stack_layout.setCurrentIndex(0)

        widget = QWidget()
        widget.setLayout(self.stack_layout)
        self.setCentralWidget(widget)

    def login_cmd(self):
        self.stack_layout.setCurrentIndex(1)

    def logout_cmd(self):
        self.stack_layout.setCurrentIndex(0)


app = QApplication(sys.argv)

window = MainWindow()
window.show()
app.exec_()

bentraje6381 | 2020-12-01 14:16:25 UTC | #3

Thanks for the explaining what I did wrong. The code work as expected.

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setAlignment(QtCore.Qt.AlignCenter) method is not working as expected was written by Martin Fitzpatrick .

Martin Fitzpatrick has been developing Python/Qt apps for 8 years. Building desktop applications to make data-analysis tools more user-friendly, Python was the obvious choice. Starting with Tk, later moving to wxWidgets and finally adopting PyQt.

setAlignment(QtCore.Qt.AlignCenter) method is not working as expected was published in faq on November 29, 2020 (updated September 13, 2023) . Feedback & Corrections welcome in our public issue tracker.

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setAlignment(QtCore.Qt.AlignCenter) method is not working as expected

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