PyQt5 - QApplication

QApplication 类管理 GUI 应用程序的控制流和主要设置。它专门研究 QGuiApplication 和基于 QWidget 的应用程序所需的一些功能。它处理特定于小部件的初始化、完成。对于任何使用 Qt 的 GUI 应用程序，无论在任何给定时间应用程序是否有 0、1、2 或更多窗口，都只有一个 QApplication 对象。对于非基于 QWidget 的 Qt 应用程序，请改用 QGuiApplication，因为它不依赖于 QtWidgets 库。

然后我们创建一个窗口实例并使用 sys.exit(App.exec()) 命令在事件循环中执行 QApplication 对象，下面是一些与 QApplication 对象一起使用的有用且经常使用的方法和属性。

Syntax: App = QApplication(sys.argv)

Parameters:

• beep: Sounds the bell, using the default volume and sound. This function is not available in Qt for Embedded Linux
• setFont: It sets the default font of the PyQt5 Application 
• aboutQt: Displays a simple message box about Qt. The message includes the version number of Qt being used by the application. 
• closeAllWindows: Closes all top-level windows. This function is particularly useful for applications with many top-level windows.
• setAutoSipEnabled: It automatically displays the SIP when entering widgets that accept keyboard input
• setCursorFlashTime: This method sets the text cursor’s flash (blink) time in milliseconds 
• setDoubleClickInterval: This method sets the time limit in milliseconds that distinguishes a double click from two consecutive mouse clicks

例子：

我们将创建一个简单的 PyQt5 应用程序，该应用程序在执行时会发出哔哔声，并将许多属性设置为 QApplication 对象，下面是实现

Python3

# importing libraries
from PyQt5.QtWidgets import *
from PyQt5 import QtCore, QtGui
from PyQt5.QtGui import *
from PyQt5.QtCore import *
import sys
 
 
class Window(QMainWindow):
 
    def __init__(self):
        super().__init__()
 
        # setting title
        self.setWindowTitle("Python ")
 
        # setting geometry
        self.setGeometry(100, 100, 500, 400)
 
        # calling method
        self.UiComponents()
 
        # showing all the widgets
        self.show()
 
    # method for components
    def UiComponents(self):
 
        # creating a push button
        push = QPushButton("Press", self)
 
        # setting geometry to the push button
        push.setGeometry(100, 100, 120, 40)
 
        # creating a label
        label = QLabel("GeeksforGeeks", self)
 
        # setting geometry to the label
        label.setGeometry(100, 160, 200, 50)
 
        # setting alignment to the label
        label.setAlignment(Qt.AlignCenter)
 
        # font
        font = QFont("Arial", 12)
 
        # setting font to the label
        label.setFont(font)
 
        # setting style sheet to the label
        label.setStyleSheet("QLabel"
                            "{"
                            "border : 2px solid green;"
                            "background : lightgreen;"
                            "}")
 
        # hiding the label
        label.hide()
 
        # adding action method to the push button
        push.clicked.connect(lambda: do_something())
 
        # method called by the push button when pressed
        def do_something():
 
            # unhide the label
            label.show()
 
 
# create pyqt5 app
App = QApplication(sys.argv)
 
# setting cursor flashtime
App.setCursorFlashTime(100)
 
# setting application object name
App.setObjectName("GfG")
 
# setting application display name
App.setApplicationDisplayName("GfG PyQt5")
 
# beep sound will occur when application
# is opened
App.beep()
 
# message displayed about the Qt
App.aboutQt()
 
# create the instance of our Window
window = Window()
 
# start the app
sys.exit(App.exec())

输出：
当我们首先执行代码时，会显示关于 Qt 的页面

然后我们的应用程序将开始