PyQt5：使用事件绘画

Question

我是PyQt的新手我正在开发一个项目，我应该在其上实现一个功能，使用户能够使用鼠标绘制数字（数字识别系统）。所以我想要的是当按下鼠标按钮时，应用程序将开始绘制，直到按钮被释放。我制作了这个源代码，但它仍然没有工作（我想我正在努力向PaintEvent()发送信号）。

import sys
from PyQt5 import QtCore 
from PyQt5 import QtGui, QtWidgets

from PyQt5.QtWidgets import QApplication, QWidget, QInputDialog, QLineEdit, QFileDialog,QGraphicsView,QGraphicsScene,QVBoxLayout

from PyQt5.QtWidgets import (QApplication, QLabel, QWidget)
from PyQt5.QtGui import QPainter, QColor, QPen
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QPainter
from PyQt5.QtCore import pyqtSignal, QObject
from PyQt5.QtWidgets import QMainWindow, QApplication



class Communicate(QObject): 
    drawApp = pyqtSignal() 

class MyWidget(QWidget):

    def __init__(self):
        super().__init__()

        self.initUI() 

    def initUI(self):
        self.setGeometry(300, 300, 300, 220)
        self.setWindowTitle('Simple')
        self.setMouseTracking(True)
        self.label = QLabel(self)
        self.label.resize(500, 40)
        self.c = Communicate()
        self.c.drawApp.connect(self.PaintEvent())  

        self.show()


    def mousePressEvent(self, event):

        self.c.drawApp.emit()
        self.startingposx = event.x()
        self.startingposy = event.y()
        #super().mousePressEvent(event)
        print ("mouse pressed")


    def mouseMoveEvent(self, event):

        self.label.setText('Coordinates: ( %d : %d )' % (event.x(), event.y()) )
        self.y = event.y()
        self.x=event.x()  


    def PaintEvent(self,event):

           qp = QPainter()  
           qp.begin(self)

           #qp.setPen(Qt.red)
           qp.drawPoints(self,qp)
           qp.end()

           self.update()



    def mouseReleaseEvent(self,event):
        self.endingposx = event.x()
        self.endingposy = event.y()
        super().mouseReleaseEvent(event)
        print("starting point was",self.startingposx)
        print("starting point y was ",self.startingposy)
        print("ending point was ",self.endingposx)
        print("ending point was y ",self.endingposy)
        print("released")    



    def drawPoints(self,qp):

          qp.setPen(Qt.red)
          size = self.size()
          x=self.x
          y=self.y
          qp.drawPoint(x,y)     

app = QApplication(sys.argv)


widget = MyWidget()

widget.show()

app.exec_()

Answer 1

Python对大写和小写都很敏感所以要小心，这个方法叫做paintEvent。

另外你不应该直接调用paintEvent，你必须使用函数update()，这个方法将在内部调用paintEvent()。

但即使纠正这个错误你的问题也没有解决，如果你想绘制一个路径，建议使用QPainterPath，因为这会存储笔画。

class Drawer(QWidget):
    newPoint = pyqtSignal(QPoint)
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.path = QPainterPath()    

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.drawPath(self.path)

    def mousePressEvent(self, event):
        self.path.moveTo(event.pos())
        self.update()

    def mouseMoveEvent(self, event):
        self.path.lineTo(event.pos())
        self.newPoint.emit(event.pos())
        self.update()

    def sizeHint(self):
        return QSize(400, 400)

class MyWidget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QVBoxLayout())
        label = QLabel(self)
        drawer = Drawer(self)
        drawer.newPoint.connect(lambda p: label.setText('Coordinates: ( %d : %d )' % (p.x(), p.y())))
        self.layout().addWidget(label)
        self.layout().addWidget(drawer)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = MyWidget()
    w.show()
    sys.exit(app.exec_())

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