PyQt5：通过单击 QPushButton 绘制一条线

Question

我试图让它在我单击 QPushButton 时绘制一条线。然而，我现在拥有的代码在代码启动时在 beginning 处而不是 在 之后。 QPushButton 似乎不做任何绘图。

我也不太明白为什么在绘图时需要在函数中添加“事件”参数。

import sys
from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QMainWindow, QGridLayout,QPushButton, QApplication, QWidget
from PyQt5.QtCore import QSize, QCoreApplication, Qt
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.paintEvent)
        pybutton.resize(100,100)
        pybutton.move(100, 100) 

    def paintEvent(self,event):
        print('click')
        painter = QPainter(self)
        pen = QPen(Qt.red, 3)
        painter.setPen(pen)
        painter.drawLine(0,0,100,100)

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

Answer 1

您不应该直接调用paintEvent 方法，这应该由 Qt 处理，因为除了您希望 GUI 需要在其他情况下重新绘制它之外，例如当小部件调整大小、移动等时。接收paintEvent是一个QPaintEvent，返回一个矩形需要重绘，这是为了优化重绘，有时很简单，因为在这种情况下不需要使用它。

在paintEvent方法中你必须在它不为空的时候画线，所以你应该在连接到点击信号的槽中做的是用一个有效的替换那个空线，并强制@987654325使用update() 方法调用@，通知GUI 它需要重新绘制。

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(100, 100) 
        self.line = QLine()

    def draw_line(self):
        button = self.sender()
        self.line = QLine(QPoint(), button.pos())
        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 2

import sys
from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication



from PyQt5.QtCore import QSize, Qt, QLine, QPoint
from PyQt5.QtGui import QPainter, QPen, QCursor


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

        self.setMinimumSize(QSize(300, 300))

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

        # self.pybutton.move(100, 100)
        self.line = QLine()
        self.statusBar()

    def draw_line(self,x,y):
        #sender = self.sender()
        pos=QPoint(x,y)
        #self.statusBar().showMessage(sender.text() + ' was pressed')
        self.line = QLine(QPoint(),pos)
        self.update()

    def paintEvent(self, event):
        # QMainWindow.paintEvent(self, event)

        qp = QPainter()
        qp.begin(self)
        pen = QPen(Qt.red, 2, Qt.SolidLine)
        qp.setPen(pen)
        qp.drawLine(self.line)
        qp.end()

    #def mousePressEvent(self, event):
     #   self.pybutton.move(event.x(), event.y())

    def mouseMoveEvent(self,vent):
        self.pybutton.move(vent.x(),vent.y())
        self.draw_line(vent.x(),vent.y())



if __name__ == "__main__":
    app = QApplication(sys.argv)
    mainWin = MainWindow()
    main`enter code here`Win.show()
    sys.exit(app.exec_())