Drawing line and points in PySide2 with coordination

Question

I want to draw some lines and points by PySide2 and I followed the documentations and provide code below, but it is not showing any thing after I call the function.

class Window2(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Deformed Structure")

        self.DrawWindows = QtGui.QWindow()

        self.DrawButton23 = QPushButton('Draw', self)
        self.DrawButton23.setStyleSheet("Background-color: orange")
        self.DrawButton23.move(100, 200)
        self.DrawButton23.show()

        self.DrawButton23.clicked.connect(self.PaintEvent)

    def PaintEvent(self, painter):
        painter = QtGui.QPainter()
        painter.begin(self)
        pen = QPen(Qt.green)
        painter.setPen(pen)

        for i in range(0, 10):
            x0 = i * 30
            y0 = i * 30
            x1 = 100 + i * 50
            y1 = 100 + i * 50
            point1 = QPointF(x0, y0)
            point2 = QPointF(x1, y1)
            line1 = QLineF(point1, point2)
            painter.drawPoint(point1)
            painter.drawLine(line1)
            print("OK123") #Just to check the loop, it prints 10 time

        painter.end()

Answer 1

You must understand that:

• Python and C++ are case sensitive so paintEvent is different from PaintEvent.

• You should not invoke paintEvent directly but using the update() or repaint() method.

• From what I understand is that you want the painting to be executed when you press the button but you cannot control the painting directly, the logic is to activate a certain part of the painting using some flag.

Considering the above, the solution is:

from PySide2 import QtCore, QtGui, QtWidgets


class Window2(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Deformed Structure")

        self.flag = False

        self.draw_button = QtWidgets.QPushButton("Draw", self)
        self.draw_button.setStyleSheet("Background-color: orange")
        self.draw_button.move(100, 200)

        self.draw_button.clicked.connect(self.on_clicked)

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

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

        if self.flag:
            pen = QtGui.QPen(QtCore.Qt.green)
            painter.setPen(pen)
            for i in range(0, 10):
                x0 = i * 30
                y0 = i * 30
                x1 = 100 + i * 50
                y1 = 100 + i * 50
                point1 = QtCore.QPointF(x0, y0)
                point2 = QtCore.QPointF(x1, y1)
                line1 = QtCore.QLineF(point1, point2)
                painter.drawPoint(point1)
                painter.drawLine(line1)


if __name__ == "__main__":
    app = QtWidgets.QApplication()
    w = Window2()
    w.show()
    app.exec_()