python3+PyQt5 重新实现QT事件处理程序

转载自 http://blog.sina.com.cn/s/blog_c22e36090102wzxq.html
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。

zhangji16@zhangji16vm:~/c_study/python3_study/qt_study/qpaint_prj$ cat contextMenuEvent_demo.py 
#!/usr/bin/env python
# coding=utf-8
import sys
from PyQt5.QtCore import (QEvent, QTimer, Qt)
from PyQt5.QtWidgets import (QApplication, QMenu, QWidget)
from PyQt5.QtGui import QPainter

class 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_()

run 一下程序