PyQt6登录界面：如何重置窗口状态或正确重启应用？

错误原因分析 #

你在点击Exit按钮时重新创建QApplication并调用exec()，但原有的事件循环仍在运行，导致出现QCoreApplication::exec: The event loop is already running错误。下面针对你的两个问题给出解决方案：

1. 正确的窗口重启方式 #

方式一：重启整个应用进程 #

如果需要完全重置所有应用状态，可以先退出当前进程，再重新启动脚本：

import subprocess
import sys

def exit_pro(self):
    MainWindow.close()
    # 重启当前Python脚本
    subprocess.Popen([sys.executable] + sys.argv)
    sys.exit()

方式二：销毁旧窗口并创建新窗口 #

仅重置登录窗口的话，无需重启进程，直接销毁当前窗口实例并创建新窗口即可：

def exit_pro(self):
    # 关闭并销毁当前窗口
    MainWindow.close()
    MainWindow.deleteLater()
    
    # 创建新的登录窗口
    new_window = QtWidgets.QMainWindow()
    new_ui = Ui_MainWindow()
    new_ui.setupUi(new_window)
    new_window.show()

2. 直接重置窗口状态与清空输入框 #

无需关闭重启窗口，编写一个重置函数即可实现需求，更高效简洁：

步骤1：记录窗口初始状态 #

在setupUi方法中添加初始状态记录：

def setupUi(self, MainWindow):
    MainWindow.setObjectName("MainWindow")
    MainWindow.resize(800, 600)
    # 保存窗口初始大小和位置
    self.initial_size = MainWindow.size()
    self.initial_pos = MainWindow.pos()
    
    # ... 剩余原有代码 ...

步骤2：编写重置函数 #

添加负责重置状态的函数：

def reset_window(self, MainWindow):
    # 恢复窗口到初始大小、位置，先退出最大化/最小化状态
    MainWindow.showNormal()
    MainWindow.resize(self.initial_size)
    MainWindow.move(self.initial_pos)
    
    # 清空用户名和密码输入框
    self.lineEdit.clear()
    self.lineEdit_2.clear()

步骤3：修改按钮点击事件 #

将Exit按钮的点击事件绑定到重置函数（建议把按钮文本改成"Reset"更贴合功能）：

# 在setupUi方法中修改信号连接
self.pushButton1.clicked.connect(lambda: self.reset_window(MainWindow))

完整修改后的代码示例 #

import sys
from sqlite3 import *

from PyQt6 import QtCore, QtGui, QtWidgets
from PyQt6.QtWidgets import (QApplication, QLabel, QMainWindow, QPushButton,
                             QVBoxLayout, QWidget)

file = connect("login_db.db")
cursor = file.cursor()
location = """SELECT * FROM Login"""
cursor.execute(location)
records = cursor.fetchall()
print("All records:",records)


class AnotherWindow(QWidget):
    def __init__(self):
        super().__init__()
        layout = QVBoxLayout()
        self.label = QLabel("Another Window")
        layout.addWidget(self.label)
        self.setLayout(layout)


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        # 记录窗口初始大小和位置
        self.initial_size = MainWindow.size()
        self.initial_pos = MainWindow.pos()
        
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setGeometry(QtCore.QRect(290, 120, 251, 41))
        self.lineEdit.setText("")
        self.lineEdit.setObjectName("lineEdit")

        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(220, 120, 71, 41))
        self.label.setObjectName("label")

        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(220, 180, 71, 41))
        self.label_2.setObjectName("label_2")

        self.lineEdit_2 = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit_2.setGeometry(QtCore.QRect(290, 180, 251, 41))
        self.lineEdit_2.setText("")
        self.lineEdit_2.setObjectName("lineEdit_2")

        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(490, 240, 151, 51))
        self.pushButton.setObjectName("pushButton")

        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 24))
        self.menubar.setObjectName("menubar")

        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")

        self.pushButton1 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton1.setGeometry(QtCore.QRect(200, 240, 151, 51))
        self.pushButton1.setObjectName("pushButton1")

        MainWindow.setStatusBar(self.statusbar)

        self.pushButton.clicked.connect(self.login_f)
        # 绑定重置函数
        self.pushButton1.clicked.connect(lambda: self.reset_window(MainWindow))

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
    
    def reset_window(self, MainWindow):
        # 重置窗口状态
        MainWindow.showNormal()
        MainWindow.resize(self.initial_size)
        MainWindow.move(self.initial_pos)
        # 清空输入框
        self.lineEdit.clear()
        self.lineEdit_2.clear()

    def login_f(self):
        username = self.lineEdit.text()
        password = self.lineEdit_2.text()
        if username == "" or password == "":
            print("You haven't entered your username or password")
            valid_inp = False
        else:
            valid_inp = True
        user_found = False
        pass_right = False
        if valid_inp == True:
            for row in records:
                if username == row[0]:
                    user_found = True
                    if row[1] == password:
                        pass_right = True
            if user_found == False or pass_right == False:
                print("wrong username or password")
            elif user_found == True and pass_right == True:
                print("Right password and username")
    
    def show_new_window(self, checked):
        w = AnotherWindow()
        w.show()
        
    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "Username:"))
        self.label_2.setText(_translate("MainWindow", "Password:"))
        self.pushButton.setText(_translate("MainWindow", "Log in"))
        self.pushButton1.setText(_translate("MainWindow", "Reset"))


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec())

内容的提问来源于stack exchange，提问作者ExcitdGaMeR