如何在 Python 中使用 PyQt5 绘制折线？答案

【问题标题】：How to draw polyline with PyQt5 in Python?如何在 Python 中使用 PyQt5 绘制折线？
【发布时间】：2020-02-26 12:28:56
【问题描述】：

我想用鼠标事件绘制折线。但我无法通过单击或选择笔类型来设置端点。我想画直线，但是当我写这段代码时，它只显示点而不是画线。这是我的代码：

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_())

【问题讨论】：

标签： python pyqt5 qpainter

【解决方案1】：

如果分析OP代码，起点和终点重合，所以在同一位置的2个点之间画线时，只会画一个点。逻辑是将第i步得到的点与第(i+1)个点连接起来。

做上面最简单的事情就是使用一个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_())

【讨论】：