详解PyQt5 事件处理机制

import sys
from PyQt5.QtWidgets import (QApplication, QMenu, QWidget)
from PyQt5.QtCore import (QEvent, QTimer, Qt)
from PyQt5.QtGui import QPainter

class MyEventDemoWindow(QWidget):
    def __init__(self, parent=None):
        super(MyEventDemoWindow, self).__init__(parent)
        self.justDoubleClikcked = False
        self.key = ""
        self.text = ""
        self.message = ""
        self.resize(400, 300)
        self.move(100, 100)
        self.setWindowTitle("Events Demo 1")
        QTimer.singleShot(1000, self.giveHelp)


    def giveHelp(self):
        self.text = "请点击这里触发追踪鼠标功能"
        self.update() # 重绘事件，也就是除非paintEvent函数
    
    # 重新实现关闭事件
    def closeEvent(self, event):
        print("Closed")
    
    # 重新实现上下文菜单事件
    def contextMenuEvent(self, event):
        menu = QMenu(self)
        oneAction = menu.addAction("&One")
        twoAction = menu.addAction("&Two")
        oneAction.triggered.connect(self.one)
        twoAction.triggered.connect(self.two)
        if not self.message:
            menu.addSeparator()
            threeAction = menu.addAction("&Three")
            threeAction.triggered.connect(self.three)
        menu.exec_(event.globalPos())
        
    def one(self):
        self.message = "Menu Option One"
        self.update()
    
    def two(self):
        self.message = "Menu Option Two"
        self.update()

    def three(self):
        self.message = "Menu Option Three"
        self.update()

    '''重新实现绘制事件'''
    def paintEvent(self, event):
        text = self.text
        i = text.find("\n\n")
        if i >= 0:
            text = text[0:i]
        if self.key:
            text += "\n\n你按下了：{0}".format(self.key)
        painter = QPainter(self)
        painter.setRenderHint(QPainter.TextAntialiasing)
        painter.drawText(self.rect(), Qt.AlignCenter, text) # 绘制文本
        if self.message:
            painter.drawText(self.rect(), Qt.AlignBottom | Qt.AlignHCenter, self.message)
            QTimer.singleShot(5000, self.clearMessage)
            QTimer.singleShot(5000, self.update)

    # 清空文本信息槽函数
    def clearMessage(self):
        self.message = ""
        
    # 重新实现调整窗口大小事件
    def resizeEvent(self, event):
        self.text = "调整窗口大小为： QSize({0}, {1})".format(event.size().width(), event.size().height())
        self.update()
    
    # 重新实现鼠标释放事件
    def mouseReleaseEvent(self, event) -> None:
        if self.justDoubleClikcked:
            self.justDoubleClikcked = False
        else :
            self.setMouseTracking(not self.hasMouseTracking()) # 单击鼠标
            if self.hasMouseTracking():
                self.text = "你释放了鼠标 开启鼠标跟踪功能.\n\n" + \
                        "请移动鼠标\n\n" + \
                        "单击鼠标可以关闭这个功能"
            else:
                self.text = "你释放了鼠标  关闭鼠标跟踪功能" + \
                        "单击鼠标可以开启这个功能"
        self.update()
 
    '''重新实现鼠标移动事件'''
    def mouseMoveEvent(self, event):
        if not self.justDoubleClikcked:
            globalPos = self.mapToGlobal(event.pos())# 将窗口坐标转换为屏幕坐标
            self.text = """鼠标位置：
            窗口坐标为：QPoint({0}, {1})
            屏幕坐标为：QPoint({2}, {3})""".format(event.pos().x(), event.pos().y(), globalPos.x(), globalPos.y())
            self.update()

    '''重新实现鼠标双击事件'''
    def mouseDoubleClickEvent(self, event):
        self.justDoubleClikcked = True
        self.text = "你双击了鼠标"
        self.update()

    def mousePressEvent(self, event):
        self.text = "你按下了鼠标"
        self.update()

    def keyPressEvent(self, event):
        self.text = "你按下了按键"
        self.key = ""
        if event.key() == Qt.Key_Home:
            self.key = "Home"
        elif event.key() == Qt.Key_End:
            self.key = "End"
        elif event.key() == Qt.Key_PageUp:
            if event.modifiers() & Qt.ControlModifier:
                self.key = "Ctrl + Page Up"
            else:
                self.key = "Page Up"
        elif event.key() == Qt.Key_PageDown:
            if event.modifiers() & Qt.ControlModifier:
                self.key = "Ctrl + Key_PageDown"
            else:
                self.key = "Key_PageDown"
        elif Qt.Key_A <= event.key() <= Qt.Key_Z:
            if event.modifiers() & Qt.ShiftModifier:
                self.key = "Shift+"
            self.key += event.text()
            
        if self.key:
            self.key = self.key
            self.update()
        else:
            QWidget.keyPressEvent(self, event)
    
    def keyReleaseEvent(self, event):
        self.text = "你释放了按键"
        self.update()

    '''重新实现event，捕获Tab键'''
    def event(self, event):
        if (event.type() == QEvent.KeyPress and event.key() == Qt.Key_Tab):
            self.key = "在event() 中捕获Tab键"
            self.update()
            return True # 返回True表示本次事件已经执行处理
        else:
            return QWidget.event(self, event) # 继续处理事件
        
if __name__ == "__main__":
    app = QApplication(sys.argv)
    win = MyEventDemoWindow()
    win.show()
    sys.exit(app.exec_())

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

class EventFilter(QDialog):
    def __init__(self, parent=None):
        super(EventFilter, self).__init__(parent)
        self.setWindowTitle("事件过滤器")

        self.label1 = QLabel("请点击")
        self.label2 = QLabel("请点击")
        self.label3 = QLabel("请点击")
        self.LabelState = QLabel("test")

        self.image1 = QImage("pyqt5/images/cartoon1.ico")
        self.image2 = QImage("pyqt5/images/cartoon1.ico")
        self.image3 = QImage("pyqt5/images/cartoon1.ico")

        self.width = 600
        self.height = 300

        self.resize(self.width, self.height)

        self.label1.installEventFilter(self)
        self.label2.installEventFilter(self)
        self.label3.installEventFilter(self)

        mainLayout = QGridLayout(self)
        mainLayout.addWidget(self.label1, 500, 0)
        mainLayout.addWidget(self.label2, 500, 1)
        mainLayout.addWidget(self.label3, 500, 2)
        mainLayout.addWidget(self.LabelState, 600, 1)
        self.setLayout(mainLayout)

    def eventFilter(self, watched, event):
        # print(type(watched))
        if watched == self.label1: # 只对label1的点击事件进行过滤，重写其行为，其它事件会被忽略
            if event.type() == QEvent.MouseButtonPress: # 这里对鼠标按下事件进行过滤，重写其行为
                mouseEvent = QMouseEvent(event)
                if mouseEvent.buttons() == Qt.LeftButton:
                    self.LabelState.setText("按下鼠标左键")
                elif mouseEvent.buttons() == Qt.MidButton:
                    self.LabelState.setText("按下鼠标中键")
                elif mouseEvent.buttons() == Qt.RightButton:
                    self.LabelState.setText("按下鼠标右键")

                '''转换图片大小'''
                transform = QTransform()
                transform.scale(0.5, 0.5)
                tmp = self.image1.transformed(transform)
                self.label1.setPixmap(QPixmap.fromImage(tmp))

            if event.type() == QEvent.MouseButtonRelease: # 这里对鼠标释放事件进行过滤，重写其行为
                self.LabelState.setText("释放鼠标按键")
                self.label1.setPixmap(QPixmap.fromImage(self.image1))
        return QDialog.eventFilter(self, watched, event) # 对于其它情况，会返回系统默认的事件处理方法
    
if __name__ == "__main__":
    app = QApplication(sys.argv)
    win = EventFilter()
    win.show()
    app.exec_()