尝试在加载的 QPixMap 图像上绘制时崩溃答案

【问题标题】：Crash when trying to paint on loaded QPixMap image尝试在加载的 QPixMap 图像上绘制时崩溃
【发布时间】：2019-02-02 23:06:33
【问题描述】：

我正在从事一个基本上是 Paint 的项目。我实现了打开文件功能，所以当我打开文件时它会加载到 QPixmap 中。

问题是：当我尝试在成功加载的 QPixmap 上绘图时，我的应用程序崩溃（没有错误或其他什么，它只是自行关闭）。我将提供用于绘制和打开文件的代码。我认为在这种情况下，其余的（UI 等）是不必要的。

绘图：

class Canvas(QLabel):
    def __init__(self, parent=None):
        super().__init__(parent)
        p = self.palette()
        p.setColor(self.backgroundRole(), Qt.white)
        self.setAutoFillBackground(True)
        self.setPalette(p)
        self.myPixmap = QPixmap(600, 600)
        self.painter = QPainter(self.myPixmap)
        self.pen = QPen()
        self.painter.setPen(self.pen)
        self.painter.fillRect(0, 0, 600, 600, Qt.white)
        self.setPixmap(self.myPixmap)
        self.last = None    

    def mouseMoveEvent(self, event):
        if self.last:
            self.painter.setPen(self.pen)
            self.painter.drawLine(self.last, event.pos())

            self.last = event.pos()
            self.setPixmap(self.myPixmap)
            self.update()

    def mousePressEvent(self, event):
        self.last = event.pos()

    def mouseReleaseEvent(self, event):
        self.last = None

打开文件：

def openFile(self):
    openFile_file = QFileDialog.getOpenFileName(None, 'Open File:', '', 'Images (*.png *.bmp *.jpg)')
    openFile_ok = self.canvas.myPixmap.load(openFile_file[0])
    self.canvas.setPixmap(self.canvas.myPixmap)
    self.canvas.update()
    print('open', openFile_ok)

【问题讨论】：

标签： python pyqt pyqt5

【解决方案1】：

两个主要问题是 1) 没有结束施工中完成的绘画和 2) 加载新图像后没有重置画家。

import sys
from PyQt5.QtGui import QPixmap, QPainter, QPen
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QLabel, QFileDialog

class Canvas(QLabel):
    def __init__(self, parent=None):
        super().__init__(parent)
        p = self.palette()
        p.setColor(self.backgroundRole(), Qt.white)
        self.setAutoFillBackground(True)
        self.setPalette(p)
        self.myPixmap = QPixmap(600, 600)
        self.painter = QPainter(self.myPixmap)
        self.pen = QPen()
        self.painter.setPen(self.pen)
        self.painter.fillRect(0, 0, 600, 600, Qt.white)
        self.painter.end()  # Need to end the painting here
        self.setPixmap(self.myPixmap)

        self.last = None
        self.image_loaded = False

    def mouseMoveEvent(self, event):
        if self.last:
            self.painter.setPen(self.pen)
            self.painter.drawLine(self.last, event.pos())

            self.last = event.pos()
            self.setPixmap(self.myPixmap)
            self.update()

    def mousePressEvent(self, event):
        if not self.image_loaded:
            self.openFile()
            self.image_loaded = True
        self.last = event.pos()

    def mouseReleaseEvent(self, event):
        self.last = None

    def openFile(self):
        openFile_file = QFileDialog.getOpenFileName(None, 'Open File:', '', 'Images (*.png *.bmp *.jpg)')
        openFile_ok = self.myPixmap.load(openFile_file[0])
        self.setPixmap(self.myPixmap)

        self.painter = QPainter(self.myPixmap)  # Need to reset the painter...there may be another method without creating a new painter
        self.painter.setPen(self.pen)

        self.update()
        print('open', openFile_ok)

app = QApplication(sys.argv)
label = Canvas()
label.show()
sys.exit(app.exec_())

【讨论】：