PyQt5 tutorial(Custom widgets)

Sat 14 October 2017 by Little Captain

Custom widgets are created by using the drawing tools provided by the toolkit. There are two basic possibilities: a programmer can modify or enhance an existing widget or he can create a custom widget from scratch.

Burning widget

This is a widget that we can see in Nero, K3B, or other CD/DVD burning software.

from PyQt5.QtWidgets import (QWidget, QSlider, QApplication,
                             QHBoxLayout, QVBoxLayout)
from PyQt5.QtCore import QObject, Qt, pyqtSignal
from PyQt5.QtGui import QPainter, QFont, QColor, QPen
import sys


class Communicate(QObject):
    updateBW = pyqtSignal(int)


class BurningWidget(QWidget):
    def __init__(self):
        super().__init__()

        self.initUI()

    def initUI(self):

        self.setMinimumSize(1, 30)
        self.value = 75
        self.num = [75, 150, 225, 300, 375, 450, 525, 600, 675]

    def setValue(self, value):

        self.value = value

    def paintEvent(self, e):

        qp = QPainter()
        qp.begin(self)
        self.drawWidget(qp)
        qp.end()

    def drawWidget(self, qp):

        MAX_CAPACITY = 700
        OVER_CAPACITY = 750

        font = QFont('Serif', 7, QFont.Light)
        qp.setFont(font)

        # We draw the widget dynamically.
        # The greater is the window,
        # the greater is the burning widget
        # and vice versa. That is why we must calculate
        # the size of the widget onto which we draw the custom widget.
        # The till parameter determines the total size to be drawn.
        # This value comes from the slider widget.
        # It is a proportion of the whole area.
        # The full parameter determines the point
        # where we begin to draw in red colour.

        # The actual drawing consists of three steps.
        # We draw the yellow or the red and yellow rectangle.
        # Then we draw the vertical lines which divide
        # the widget into several parts.
        # Finally, we draw the numbers which indicate the capacity of the medium.
        size = self.size()
        w = size.width()
        h = size.height()

        step = int(round(w / 10))

        till = int(((w / OVER_CAPACITY) * self.value))
        full = int(((w / OVER_CAPACITY) * MAX_CAPACITY))

        if self.value >= MAX_CAPACITY:

            qp.setPen(QColor(255, 255, 255))
            qp.setBrush(QColor(255, 255, 184))
            qp.drawRect(0, 0, full, h)
            qp.setPen(QColor(255, 175, 175))
            qp.setBrush(QColor(255, 175, 175))
            qp.drawRect(full, 0, till - full, h)

        else:

            qp.setPen(QColor(255, 255, 255))
            qp.setBrush(QColor(255, 255, 184))
            qp.drawRect(0, 0, till, h)

        pen = QPen(QColor(20, 20, 20), 1,
                   Qt.SolidLine)

        qp.setPen(pen)
        qp.setBrush(Qt.NoBrush)
        qp.drawRect(0, 0, w - 1, h - 1)

        j = 0

        for i in range(step, 10 * step, step):
            qp.drawLine(i, 0, i, 5)
            metrics = qp.fontMetrics()
            fw = metrics.width(str(self.num[j]))
            qp.drawText(i - fw / 2, h / 2, str(self.num[j]))
            j = j + 1


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

        self.initUI()

    def initUI(self):
        OVER_CAPACITY = 750

        sld = QSlider(Qt.Horizontal, self)
        sld.setFocusPolicy(Qt.NoFocus)
        sld.setRange(1, OVER_CAPACITY)
        sld.setValue(75)
        sld.setGeometry(30, 40, 150, 30)

        self.c = Communicate()
        self.wid = BurningWidget()
        self.c.updateBW[int].connect(self.wid.setValue)

        sld.valueChanged[int].connect(self.changeValue)
        hbox = QHBoxLayout()
        hbox.addWidget(self.wid)
        vbox = QVBoxLayout()
        vbox.addStretch(1)
        vbox.addLayout(hbox)
        self.setLayout(vbox)

        self.setGeometry(300, 300, 390, 210)
        self.setWindowTitle('Burning widget')
        self.show()

    def changeValue(self, value):
        self.c.updateBW.emit(value)
        self.wid.repaint()


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