Pyqt5 在两个小部件之间画一条线

Question

I am trying to use QPainter to draw a line between two widgets. If I use a simple function inside the first class it works. But, I want to create a separate class of a QPainter event, that I can call at the first class whenever I want. But, it is not working as expected. Can you help me to figure out why the QPainter class is not adding a line.

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

class Example(QWidget):

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

        self.initUI()


    def initUI(self):

        self.okButton = QPushButton("OK")
        self.cancelButton = QPushButton("Cancel")

        l1 = self.okButton.pos()
        l2 = self.cancelButton.pos()

        # This is to call the class to draw a line between those two widgets
        a = QPaint(l1.x(), l1.y(), l2.x(), l2.y(),parent=self)

        vbox = QVBoxLayout()
        vbox.addWidget(self.okButton)
        vbox.addWidget(self.cancelButton)

        self.setLayout(vbox)    

        self.setGeometry(300, 300, 300, 150)
        self.setWindowTitle('Buttons')    
        self.show()


class QPaint(QPainter):
    def __init__(self, x1, y1, x2, y2, parent=None):
        super().__init__()

    def paintEvent(self, event):

        self.setPen(Qt.red)

        self.drawLine(x1,y1,x2,y2)


if __name__ == '__main__':

    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

Answer 1

Widgets can only be painted in the widget's paintEvent method, so if you don't want to paint it in the same class then you can use multiple inheritance. On the other hand, the initial positions you use to paint will be the positions before showing that they are 0 making no line is painted but a point so it is better to track the positions using an event filter.

import sys

from PyQt5.QtCore import QEvent
from PyQt5.QtGui import QPainter
from PyQt5.QtWidgets import QApplication, QPushButton, QVBoxLayout, QWidget


class Drawer:
    def paintEvent(self, event):
        painter = QPainter(self)
        painter.drawLine(self.p1, self.p2)


class Example(QWidget, Drawer):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.initUI()

    def initUI(self):
        self.okButton = QPushButton("OK")
        self.cancelButton = QPushButton("Cancel")

        vbox = QVBoxLayout(self)
        vbox.addWidget(self.okButton)
        vbox.addWidget(self.cancelButton)

        self.setGeometry(300, 300, 300, 150)
        self.setWindowTitle("Buttons")

        self.p1, self.p2 = self.okButton.pos(), self.cancelButton.pos()

        self.okButton.installEventFilter(self)
        self.cancelButton.installEventFilter(self)

    def eventFilter(self, o, e):
        if e.type() == QEvent.Move:
            if o is self.okButton:
                self.p1 = self.okButton.pos()
            elif o is self.cancelButton:
                self.p2 = self.cancelButton.pos()
            self.update()
        return super().eventFilter(o, e)


if __name__ == "__main__":

    app = QApplication(sys.argv)
    ex = Example()
    ex.show()
    sys.exit(app.exec_())