如何在 Python 中使用 PyQt5 绘制折线？

Question

I want to draw polyline with mouse event. But I can't set endpoints by clicking, or choose pen type. I want to draw linear lines, but when i write this code it only shows dots instead of drawing a line. Here is my code:

import sys
from PyQt5 import QtWidgets, QtCore
from PyQt5.QtGui import QPainter, QBrush, QColor, QPen, QPainterPath
from PyQt5.QtWidgets import QLabel, QGraphicsScene, QGraphicsView


class MyWidget(QtWidgets.QWidget):
def __init__(self):
    super().__init__()
    self.begin = QtCore.QPoint()
    self.end = QtCore.QPoint()
    self.beginList = []
    self.endList = []
    self.initUI()

def initUI(self):
    self.setGeometry(200, 200, 1000, 500)
    self.label = QLabel(self)
    self.label.resize(500, 40)
    self.show()

def paintEvent(self, event):
    qp = QPainter(self)
    for i,j in zip(self.beginList, self.endList):
        qp.drawLines(QtCore.QLineF(i,j))


def mouseMoveEvent(self, event):
    self.begin = event.pos()
    self.end = event.pos()
    self.beginList.append(self.begin)
    self.endList.append(self.end)
    self.label.setText('Coordinates: ( %d : %d )' % (event.x(), event.y()))
    self.update()

def mouseReleaseEvent(self, event):
    self.begin = event.pos()
    self.end = event.pos()

if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
window = MyWidget()
window.resize(800,600)
sys.exit(app.exec_())

Answer 1

If the OP code is analyzed, the starting point and the end point coincide, so when drawing a line between 2 points of the same location, only one point will be drawn. The logic is to join the point obtained in the i-th step with the (i+1)-th point.

To do the above the simplest thing is to use a QPainterPath:

import sys
from PyQt5 import QtWidgets, QtGui, QtCore


class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()
        self.paths = []

    def initUI(self):
        self.setGeometry(200, 200, 1000, 500)
        self.label = QtWidgets.QLabel(self)
        self.show()

    def paintEvent(self, event):
        qp = QtGui.QPainter(self)
        for path in self.paths:
            qp.drawPath(path)

    def mousePressEvent(self, event):
        path = QtGui.QPainterPath()
        path.moveTo(event.pos())
        self.paths.append(path)
        super().mousePressEvent(event)

    def mouseMoveEvent(self, event):
        self.paths[-1].lineTo(event.pos())
        self.label.setText('Coordinates: ( %d : %d )' % (event.x(), event.y()))
        self.label.adjustSize()
        self.update()
        super().mouseMoveEvent(event)

    def mouseReleaseEvent(self, event):
        self.paths[-1].lineTo(event.pos())
        self.update()
        super().mouseReleaseEvent(event)


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    window = MyWidget()
    window.resize(800, 600)
    sys.exit(app.exec_())