Signal and slot mechanism ==pyqt5

event Event

• be-all GUI Programs are event driven . The event is mainly triggered by the user ,

• But there may be other triggers ： For example, network connection 、window manager Or timer .

• When we call QApplication Of exec_() Method will cause the program to enter the main loop . The main loop gets and distributes Events .

• In event model , There are three participants ：

  • Event source ： The event source is the object whose state changes . It generates events . event ( object ) Encapsulates the change of state in the event source
  • Event object ： The event source object gives the work of event processing to the event receiver .
  • Event recipient ： The event receiver is the object to be notified

• pyqt5 There is a unique signal&slot Mechanism to handle events .

• Signal slot is used for communication between objects .signal Triggered when a particular event occurs ,slot It could be anything callable object . When signal When triggered, the... Connected to it will be called slot.

Signal and slot mechanisms

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import (QWidget,QLCDNumber,QSlider,QVBoxLayout,QApplication)

class Example(QWidget):
    def __init__(self):
        super().__init__()

        self.initUI()

    def initUI(self):
        lcd=QLCDNumber(self)# According to the component 
        sld=QSlider(Qt.Horizontal,self)# Scroll banner components 

        vbox=QVBoxLayout()# Vertical layout 
        vbox.addWidget(lcd)#add Come in 
        vbox.addWidget(sld)#add Come in 

        self.setLayout(vbox)# Direct layout 
        sld.valueChanged.connect(lcd.display)# Turn the scroll bar to valueChanged Signal connected to lcd Of display slot .---------------------------

        self.setGeometry(300,300,250,150)
        self.setWindowTitle('signal&slot')
        self.show()

if __name__ == '__main__':
    app=QApplication(sys.argv)
    ex=Example()
    sys.exit(app.exec_())

The sender of the event

#  Sometimes you need to know which control is sending the signal . Regarding this PyQt5 Provides sender() Method .
import sys
from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication

class Example(QMainWindow):

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

        self.initUI()

    def initUI(self):
        btn1 = QPushButton("Button 1", self)
        btn1.move(30, 50)

        btn2 = QPushButton("Button 2", self)
        btn2.move(150, 50)

        btn1.clicked.connect(self.buttonClicked)
        btn2.clicked.connect(self.buttonClicked)

        self.statusBar()

        self.setGeometry(300, 300, 290, 150)
        self.setWindowTitle('Event sender')
        self.show()

    def buttonClicked(self):# The two buttons are connected to the same slot .
        sender = self.sender()
        self.statusBar().showMessage(sender.text() + ' was pressed')


# ===================================================================== Signal 
#  adopt QObject The created object can signal . The following example demonstrates how to emit a custom signal 
import sys
from PyQt5.QtCore import pyqtSignal, QObject
from PyQt5.QtWidgets import QMainWindow, QApplication

class Communicate(QObject):# This signal is triggered when the mouse is pressed , It connects QMainWindow Of close() slot .
    closeApp = pyqtSignal()

class Example1(QMainWindow):

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

        self.initUI()

    def initUI(self):
        self.c = Communicate()
        self.c.closeApp.connect(self.close)

        self.setGeometry(300, 300, 290, 150)
        self.setWindowTitle('Emit signal')
        self.show()

    def mousePressEvent(self, event):
        self.c.closeApp.emit()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example1()
    sys.exit(app.exec_())

The receiver of the event

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QWidget, QApplication


class Example(QWidget):

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

        self.initUI()

    def initUI(self):
        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Event handler')
        self.show()

    def keyPressEvent(self, e):
        if e.key() == Qt.Key_Escape:
            self.close()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())