一个画笔程序画不出线，只有一个点

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'Demo.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.
import math
import sys

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtCore import Qt, QPoint, QPointF
from PyQt5.QtGui import QPainter, QPen, QPainterPath, QPolygonF, QColor, QPixmap
from PyQt5.QtWidgets import QApplication, QWidget, QFrame, QSizePolicy, QColorDialog, QHBoxLayout, QPushButton, \
    QComboBox, QSpinBox, QFormLayout, QLabel


class MyLabel(QLabel):
    def __init__(self, parent=None):
        super(MyLabel, self).__init__(parent)
        self.flag = None
        self.setLineWidth(1)
        self.setMidLineWidth(0)
        self.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Preferred)

        self.x0 = 0
        self.y0 = 0
        self.x1 = 0
        self.y1 = 0
        self.penColor = (QColor(255, 0, 0, 40))
        self.lastpenColor = (QColor(255, 0, 0, 40))
        self.penWidth = 30
        self.penStyle = Qt.SolidLine
        self.capStyle = Qt.RoundCap

    def setPenColor(self, color):
        self.lastpenColor = color
        self.penColor = color

    def setDrawStatus(self, status):
        if status == True:
            self.penColor = self.lastpenColor
        elif status == False:
            self.penColor = (QColor(0, 0, 0, 0))

    def widthChange(self, value):
        self.penWidth = value

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setRenderHint(QPainter.Antialiasing, True)

        # 绘制边框线
        painter.drawRect(self.rect())

        painter.setPen(QPen(self.penColor, self.penWidth, self.penStyle, self.capStyle))
        painter.drawLine(self.x0, self.y0, self.x1, self.y1)

    def mousePressEvent(self, event):
        self.x1 = event.x()
        self.y1 = event.y()
        self.flag = True

    def mouseMoveEvent(self, event):
        if self.flag:
            self.x0 = self.x1
            self.y0 = self.y1
            self.x1 = event.x()
            self.y1 = event.y()
            self.update()

    def mouseReleaseEvent(self, event):
        self.flag = False

class Widget(QWidget):
    def __init__(self,parent=None):
        super(Widget,self).__init__(parent)
        self.resize(1000, 400)
        self.initUi()

    def initUi(self):
        self.canvas = MyLabel()
        layout = QHBoxLayout()

        btnPen = QPushButton('画笔')
        btnPen.clicked.connect(self.DrawOn)

        penColor = QComboBox()
        penColor.addItems(['红色 肿瘤','绿色 间质', '紫色 坏死', '蓝色 淋巴'])
        penColor.currentTextChanged.connect(self.ColorChange)

        btnEraser = QPushButton('橡皮擦')
        btnEraser.clicked.connect(self.DrawOff)

        penWidth = QSpinBox()
        penWidth.resize(20,30)
        penWidth.setRange(20,60)
        penWidth.setValue(30)
        penWidth.valueChanged.connect(self.canvas.widthChange)

        fLayout = QFormLayout()
        fLayout.setContentsMargins(0, 0, 0, 0)
        fLayout.addRow(btnPen)
        fLayout.addRow(penColor)
        fLayout.addRow(btnEraser)
        fLayout.addRow(penWidth)

        wid_left = QWidget()
        wid_left.setMaximumWidth(200)
        wid_left.setLayout(fLayout)

        layout.addWidget(wid_left)
        layout.addWidget(self.canvas)

        self.setLayout(layout)

    def DrawOn(self):
        self.canvas.setDrawStatus(True)

    def ColorChange(self, color):
        if color == '红色 肿瘤':
            self.canvas.setPenColor(QColor(255, 0, 0, 40))
        elif color == '绿色 间质':
            self.canvas.setPenColor(QColor(0, 255, 0, 40))
        elif color == '紫色 坏死':
            self.canvas.setPenColor(QColor(153, 0, 255, 40))
        elif color == '蓝色 淋巴':
            self.canvas.setPenColor(QColor(0, 0, 255, 40))

    def DrawOff(self):
        self.canvas.setDrawStatus(False)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = Widget()
    window.show()
    sys.exit(app.exec())

只能出现一个点，想要画出自由的线。

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'Demo.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.
import math
import sys

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtCore import Qt, QPoint, QPointF
from PyQt5.QtGui import QPainter, QPen, QPainterPath, QPolygonF, QColor, QPixmap
from PyQt5.QtWidgets import QApplication, QWidget, QFrame, QSizePolicy, QColorDialog, QHBoxLayout, QPushButton, \
    QComboBox, QSpinBox, QFormLayout, QLabel



class MyLabel(QLabel):
    def __init__(self, parent=None):
        super(MyLabel, self).__init__(parent)
        self.flag = None
        self.setLineWidth(1)
        self.setMidLineWidth(0)
        self.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Preferred)

        self.penColor = (QColor(255, 0, 0, 40))
        self.lastpenColor = (QColor(255, 0, 0, 40))
        self.penWidth = 30
        self.penStyle = Qt.SolidLine
        self.capStyle = Qt.RoundCap

        self.pathList = []
        self.path = QPainterPath()

    def setPenColor(self, color):
        self.lastpenColor = color
        self.penColor = color

    def setDrawStatus(self, status):
        if status == True:
            self.penColor = self.lastpenColor
        elif status == False:
            self.penColor = (QColor(0, 0, 0, 0))

    def widthChange(self, value):
        self.penWidth = value

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setRenderHint(QPainter.Antialiasing, True)

        # 绘制边框线
        painter.drawRect(self.rect())
        for p,d in self.pathList:
            painter.setPen(QPen(*d))
            painter.drawPath(p)

    def mousePressEvent(self, event):
        self.path = QPainterPath()
        self.pathList.append([self.path, (self.penColor, self.penWidth, self.penStyle, self.capStyle)])
        self.path.moveTo(event.pos())
        self.flag = True
        self.update()

    def mouseMoveEvent(self, event):
        if self.flag:
            self.path.lineTo(event.pos())
            self.update()

    def mouseReleaseEvent(self, event):
        self.flag = False

class Widget(QWidget):
    def __init__(self,parent=None):
        super(Widget,self).__init__(parent)
        self.resize(1000, 400)
        self.initUi()

    def initUi(self):
        self.canvas = MyLabel()
        layout = QHBoxLayout()

        btnPen = QPushButton('画笔')
        btnPen.clicked.connect(self.DrawOn)

        penColor = QComboBox()
        penColor.addItems(['红色 肿瘤','绿色 间质', '紫色 坏死', '蓝色 淋巴'])
        penColor.currentTextChanged.connect(self.ColorChange)

        btnEraser = QPushButton('橡皮擦')
        btnEraser.clicked.connect(self.DrawOff)

        penWidth = QSpinBox()
        penWidth.resize(20,30)
        penWidth.setRange(20,60)
        penWidth.setValue(30)
        penWidth.valueChanged.connect(self.canvas.widthChange)

        fLayout = QFormLayout()
        fLayout.setContentsMargins(0, 0, 0, 0)
        fLayout.addRow(btnPen)
        fLayout.addRow(penColor)
        fLayout.addRow(btnEraser)
        fLayout.addRow(penWidth)

        wid_left = QWidget()
        wid_left.setMaximumWidth(200)
        wid_left.setLayout(fLayout)

        layout.addWidget(wid_left)
        layout.addWidget(self.canvas)

        self.setLayout(layout)

    def DrawOn(self):
        self.canvas.setDrawStatus(True)

    def ColorChange(self, color):
        if color == '红色 肿瘤':
            self.canvas.setPenColor(QColor(255, 0, 0, 40))
        elif color == '绿色 间质':
            self.canvas.setPenColor(QColor(0, 255, 0, 40))
        elif color == '紫色 坏死':
            self.canvas.setPenColor(QColor(153, 0, 255, 40))
        elif color == '蓝色 淋巴':
            self.canvas.setPenColor(QColor(0, 0, 255, 40))

    def DrawOff(self):
        self.canvas.setDrawStatus(False)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = Widget()
    window.show()
    sys.exit(app.exec())

如有帮助，请点击我的回答下方的【采纳该答案】按钮帮忙采纳下，谢谢!

将self.update()改成：self.update(self.x0,self.y0,self.x1,self.y1)

def mouseMoveEvent(self, event):
        if self.flag:
            self.x0 = self.x1
            self.y0 = self.y1
            self.x1 = event.x()
            self.y1 = event.y()
            self.update(self.x0,self.y0,self.x1,self.y1)

如有帮助，请点采纳。

您好，我是有问必答小助手，您的问题已经有小伙伴帮您解答，感谢您对有问必答的支持与关注！
PS：问答VIP年卡 【限时加赠：IT技术图书免费领】，了解详情>>> https://vip.csdn.net/askvip?utm_source=1146287632