PyQt5：绘制新的绘图/线条时保持先前绘制的绘图/线条

Question

在绘制新线后，我无法维护先前绘制的线。现在，如果我单击一个按钮，它将绘制一条线，但是一旦我单击第二个按钮，就会绘制一条新线，并删除最初的一条线。我希望两者都保留。

import sys
from PyQt5.QtWidgets import QMainWindow,QPushButton, QApplication
from PyQt5.QtCore import QSize, Qt, QLine, QPoint
from PyQt5.QtGui import QPainter, QPen

class MainWindow(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)

        self.setMinimumSize(QSize(300, 300)) 

        pybutton = QPushButton('button', self)
        pybutton.clicked.connect(self.draw_line)
        pybutton.resize(100,100)
        pybutton.move(0, 0) 

        pybutton2 = QPushButton('button2', self)
        pybutton2.clicked.connect(self.draw_line)
        pybutton2.resize(100,100)
        pybutton2.move(200, 0) 
        self.line = QLine()

    def draw_line(self):
        button = self.sender()
        x = int(button.x()) + int(button.width())/2
        y = int(button.y())+100
        self.line = QLine(x, y, x, y+100)
        self.update()

    def paintEvent(self,event):
        QMainWindow.paintEvent(self, event)
        if not self.line.isNull():
            painter = QPainter(self)
            pen = QPen(Qt.red, 3)
            painter.setPen(pen)
            painter.drawLine(self.line)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    mainWin = MainWindow()
    mainWin.show()
    sys.exit(app.exec_())

Answer 1

短解：

将QLine 存储在列表中并重绘：

class MainWindow(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)

        self.setMinimumSize(QSize(300, 300)) 

        pybutton = QPushButton('button', self)
        pybutton.clicked.connect(self.draw_line)
        pybutton.resize(100,100)
        pybutton.move(0, 0) 

        pybutton2 = QPushButton('button2', self)
        pybutton2.clicked.connect(self.draw_line)
        pybutton2.resize(100,100)
        pybutton2.move(200, 0) 
        self.lines = []

    def draw_line(self):
        button = self.sender()
        r = button.geometry()
        p1 = QPoint(r.left() + r.width()/2, r.height())
        p2 = p1+QPoint(0, 100)
        line = QLine(p1, p2)
        if line not in self.lines:
            self.lines.append(line)
            self.update()

    def paintEvent(self,event):
        QMainWindow.paintEvent(self, event)
        painter = QPainter(self)
        pen = QPen(Qt.red, 3)
        painter.setPen(pen)
        for line in self.lines:
            painter.drawLine(line)

长解：

这类问题已经被问过无数次了，所以我将花时间扩展并给出问题的一般观点，这样我就不会每次都回答这类问题，所以这个问题 它将被改进和更新。

paintEvent()是处理Qt进行GUI重绘的方法，这个方法重绘一切，所以绘图不节省内存，所以你必须存储指令并进行绘图 按照这些说明。

我推荐使用paintEvent() 方法来创建自定义小部件，而不是将执行绘画任务的GUI 作为主要功能，因为这个Qt 提供了QGraphicsView、QGraphicsScene 和QGraphicsItems 类。

---

使用QPainter 的指令重绘任务如drawLine()、fillRect() 等会消耗资源，如果您想进行更高效的实现，最好创建一个QPixmap，您必须随时更新必要的，并使用提到的QPixmap 在paintEvent() 中重新绘制：

class MainWindow(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)

        self.setMinimumSize(QSize(300, 300)) 

        pybutton = QPushButton('button', self)
        pybutton.clicked.connect(self.draw_line)
        pybutton.resize(100,100)
        pybutton.move(0, 0) 

        pybutton2 = QPushButton('button2', self)
        pybutton2.clicked.connect(self.draw_line)
        pybutton2.resize(100,100)
        pybutton2.move(200, 0)
        self.pixmap = QPixmap(self.size())
        self.pixmap.fill(Qt.transparent)

    def draw_line(self):
        button = self.sender()
        r = button.geometry()
        p1 = QPoint(r.left() + r.width()/2, r.height())
        p2 = p1+QPoint(0, 100)
        line = QLine(p1, p2)

        p = QPainter(self.pixmap)
        pen = QPen(Qt.red, 3)
        p.setPen(pen)
        p.drawLine(line)
        p.end()

        self.update()

    def paintEvent(self,event):
        QMainWindow.paintEvent(self, event)
        painter = QPainter(self)
        painter.drawPixmap(QPoint(), self.pixmap)

    def resizeEvent(self, event):
        if self.width() > self.pixmap.width() or self.height() > self.pixmap.height():
            pixmap = QPixmap(self.size())
            pixmap.fill(Qt.transparent)
            p = QPainter(pixmap)
            p.drawPixmap(QPoint(), self.pixmap)
            self.pixmap = pixmap
        QMainWindow.resizeEvent(self, event)