PyQt. QPainter. Ошибка вызова

Question

При простом вызове QPainter:

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

class Example(QMainWindow):
    def __init__(self):
        super().__init__()
        self.show()
        qp = QPainter(self)
        qp.begin(self)
        qp.end()
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

Компилятор выдаёт следующую ошибку:

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::drawPoints: Painter not active
QPainter::end: Painter not active, aborted

Остальная программа работает, но ни какие методы QPainter такие как

drawPoint() и т.п. не работают. Что делать?

Answer 1

Операции рисования обычно выполняются в функции события paintEvent().

В этой функции мы обычно устанавливаем сначала кисть, кисть или шрифт, а затем вызываем связанные методы для рисования.

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


class Example(QWidget):
    def __init__(self):
        super(Example, self).__init__()
        self.resize(600, 600)

        self.pen1 = QPen()                          
        self.pen1.setColor(Qt.green)
        self.pen2 = QPen(Qt.SolidLine)
        self.pen2.setWidth(6)                       
        self.pen3 = QPen(Qt.DashLine)
        self.pen4 = QPen(Qt.DotLine)
        self.pen5 = QPen(Qt.DashDotLine)
        self.pen6 = QPen(Qt.DashDotDotLine)
        self.pen7 = QPen(Qt.CustomDashLine)         
        self.pen7.setDashPattern([6, 2, 18, 2])

        self.pen8 = QPen(Qt.SolidLine)              
        self.pen8.setWidth(6)
        self.pen8.setCapStyle(Qt.RoundCap)

        self.pen9 = QPen(Qt.SolidLine)              
        self.pen9.setWidthF(6)
        self.pen9.setJoinStyle(Qt.MiterJoin)

    def paintEvent(self, QPaintEvent):
        painter = QPainter(self)                    
        painter.setPen(self.pen1)
        painter.drawLine(100, 10, 500, 10)      

        painter.setPen(self.pen2)
        painter.drawLine(100, 30, 500, 30)

        painter.setPen(self.pen3)
        painter.drawLine(100, 50, 500, 50)

        painter.setPen(self.pen4)
        painter.drawLine(100, 70, 500, 70)

        painter.setPen(self.pen5)
        painter.drawLine(100, 90, 500, 90)

        painter.setPen(self.pen6)
        painter.drawLine(100, 110, 500, 110)

        painter.setPen(self.pen7)
        painter.drawLine(100, 130, 500, 130)

        painter.setPen(self.pen8)
        painter.drawLine(100, 150, 500, 150)

        painter.setPen(self.pen2)
        painter.drawRect(100, 170, 400, 200)           

        painter.setPen(self.pen9)
        painter.drawRect(100, 390, 400, 200)


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

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PyQt. QPainter. Ошибка вызова

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