PyQt5: How to click a button to start the paint?

Question

The following code makes a button and a rectangle. I would like to change it, so that the rectangle is drawn when the button is clicked.

from PyQt5.QtWidgets import QWidget, QApplication, QPushButton
from PyQt5.QtGui import QPainter, QColor, QBrush
import sys

class Example(QWidget):
    def __init__(self):
        super(Example, self).__init__()
        self.initUI()

    def initUI(self):
        self.setFixedSize(400, 400)
        self.setWindowTitle('Colours')
        self.btn = QPushButton("Paint", self)
        self.btn.move(100, 100)
        # self.btn.clicked.connect(self.paintEvent())
        self.show()

    def paintEvent(self, e):
        qp = QPainter()
        qp.begin(self)
        self.drawRectangles(qp)
        qp.end()

    def drawRectangles(self, qp):
        col = QColor(0, 0, 0)
        col.setNamedColor('#d4d4d4')
        qp.setPen(col)
        qp.setBrush(QColor(200, 0, 0))
        qp.drawRect(10, 15, 90, 60)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

Thanks for your help!

Asked By: Rt Rtt

||

Source

Answer 1

the paintEvent() method is called internally by Qt, it should not be called directly but through the update() method, but in your case you want to do it when a certain condition is used, before that you must create a flag that indicates that it should be drawn, all of the above is implemented in the following code:

class Example(QWidget):
    def __init__(self):
        super(Example, self).__init__()
        self.initUI()
        self.flag = False

    def initUI(self):
        self.setFixedSize(400, 400)
        self.setWindowTitle('Colours')
        self.btn = QPushButton("Paint", self)
        self.btn.move(100, 100)
        self.btn.clicked.connect(self.onClicked)
        self.show()

    def onClicked(self):
        self.flag = True
        self.update()


    def paintEvent(self, e):
        if self.flag:
            qp = QPainter()
            qp.begin(self)
            self.drawRectangles(qp)
            qp.end()

    def drawRectangles(self, qp):
        col = QColor(0, 0, 0)
        col.setNamedColor('#d4d4d4')
        qp.setPen(col)
        qp.setBrush(QColor(200, 0, 0))
        qp.drawRect(10, 15, 90, 60)

Answered By: eyllanesc

Answer 2

I would never ever think to create a flag if I didn’t see this post.

Answered By: Stockfish

PyQt5: How to click a button to start the paint?

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