如何在 Python 中使用 PyQt5 繪制折線？

Question

我想用鼠標事件繪制折線。 但是我無法通過單擊或選擇筆類型來設置端點。 我想畫直線，但是當我寫這段代碼時，它只顯示點而不是畫一條線。 這是我的代碼：

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

如果分析OP代碼，起點和終點重合，所以在同一位置的2個點之間畫一條線時，只會畫一個點。 邏輯是將第i步得到的點與第(i+1)點連接起來。

要做到以上最簡單的事情是使用 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_())