python3+PyQt5 重新实现QT事件处理程序

本文是对《Python Qt GUI快速编程》的第10章的例子events用Python3+PyQt5进行改写，涉及到重新实现QWidget的事件处理程序。本例子涉及到上下文菜单，鼠标事件，键盘事件，可作为重新实现事件处理程序的参考。
注：在创建上下文菜单最简单的方式使用Qwidget.addAction()把动作添加到窗口部件中，再把窗口部件的上下文菜单策略设置为Qt.ActionsContextMenu即可，但是如果像本例子一样要根据不同的状态来提供不同的选项，则要重新实现上下文菜单事件处理程序。

#!/usr/bin/env python3import sysfrom PyQt5.QtCore import (QEvent, QTimer, Qt)from PyQt5.QtWidgets import (QApplication, QMenu, QWidget)from PyQt5.QtGui import QPainterclass Widget(QWidget):    def __init__(self, parent=None):        super(Widget, self).__init__(parent)        self.justDoubleClicked = False        self.key = ""        self.text = ""        self.message = ""        self.resize(400, 300)        self.move(100, 100)        self.setWindowTitle("Events")        QTimer.singleShot(0, self.giveHelp) # Avoids first resize msg    def giveHelp(self):        self.text = "Click to toggle mouse tracking"        self.update()    def closeEvent(self, event):        print("Closed")    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("Thre&e")            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()    def paintEvent(self, event):        text = self.text        i = text.find("\n\n")        if i >= 0:            text = text[0:i]        if self.key:            text += "\n\nYou pressed: {0}".format(self.key)        painter = QPainter(self)        painter.setRenderHint(QPainter.TextAntialiasing)        painter.drawText(self.rect(), Qt.AlignCenter, text)        if self.message:            painter.drawText(self.rect(), Qt.AlignBottom|Qt.AlignHCenter,                             self.message)            QTimer.singleShot(5000, self.clearMessage)            QTimer.singleShot(5000, self.update)    def clearMessage(self):        self.message=""    def resizeEvent(self, event):        self.text = "Resized to QSize({0}, {1})".format(                            event.size().width(), event.size().height())        self.update()    def mouseReleaseEvent(self, event):        if self.justDoubleClicked:            self.justDoubleClicked = False        else:            self.setMouseTracking(not self.hasMouseTracking())            if self.hasMouseTracking():                self.text = "Mouse tracking is on.\n"+\                        "Try moving the mouse!\n"+\                        "Single click to switch it off"            else:                self.text = "Mouse tracking is off.\n"+\                                           "Single click to switch it on"            self.update()    def mouseMoveEvent(self, event):        if not self.justDoubleClicked:            globalPos = self.mapToGlobal(event.pos())            self.text = "The mouse is at\nQPoint({0}, {1}) "+\                    "in widget coords, and\n"+\                    "QPoint({2}, {3}) in screen coords".format(                    event.pos().x(), event.pos().y(), globalPos.x(),                    globalPos.y())            self.update()    def mouseDoubleClickEvent(self, event):        self.justDoubleClicked = True        self.text = "Double-clicked."        self.update()    def keyPressEvent(self, event):        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+PageUp"            else:                self.key = "PageUp"        elif event.key() == Qt.Key_PageDown:            if event.modifiers() & Qt.ControlModifier:                self.key = "Ctrl+PageDown"            else:                self.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 event(self, event):        if (event.type() == QEvent.KeyPress and            event.key() == Qt.Key_Tab):            self.key = "Tab captured in event()"            self.update()            return True        return QWidget.event(self, event)if __name__ == "__main__":    app = QApplication(sys.argv)    form = Widget()    form.show()    app.exec_()

运行结果：