main.qml

import QtQuick 2.0
import TextBalloonPlugin 1.0

Item {
    height: 480
    width: 320

    //! [0]
    ListModel {
        id: balloonModel
        ListElement {
            balloonWidth: 200
        }
        ListElement {
            balloonWidth: 120
        }
    }

    ListView {
        anchors.bottom: controls.top
        anchors.bottomMargin: 2
        anchors.top: parent.top
        id: balloonView
        delegate: TextBalloon {
            anchors.right: index % 2 == 0 ? undefined : parent.right
            height: 60
            rightAligned: index % 2 == 0 ? false : true
            width: balloonWidth
        }
        model: balloonModel
        spacing: 5
        width: parent.width
    }
    //! [0]

    //! [1]
    Rectangle {
        id: controls

        anchors.bottom: parent.bottom
        anchors.left: parent.left
        anchors.margins: 1
        anchors.right: parent.right
        border.width: 2
        color: "white"
        height: parent.height * 0.15

        Text {
            anchors.centerIn: parent
            text: "Add another balloon"
        }

        MouseArea {
            anchors.fill: parent
            hoverEnabled: true
            onClicked: {
                balloonModel.append({
                                        "balloonWidth": Math.floor(
                                                            Math.random(
                                                                ) * 200 + 100)
                                    })
                balloonView.positionViewAtIndex(balloonView.count - 1,
                                                ListView.End)
            }
            onEntered: {
                parent.color = "#8ac953"
            }
            onExited: {
                parent.color = "white"
            }
        }
    }
    //! [1]
}

painteditem.py

import sys

from PySide6.QtGui import QPainter, QBrush, QColor
from PySide6.QtWidgets import QApplication
from PySide6.QtQml import qmlRegisterType
from PySide6.QtCore import QUrl, Property, Signal, Qt, QPointF
from PySide6.QtQuick import QQuickPaintedItem, QQuickView


class TextBalloon(QQuickPaintedItem):

    rightAlignedChanged = Signal()

    def __init__(self, parent=None):
        self._rightAligned = False
        super().__init__(parent)

    @Property(bool, notify=rightAlignedChanged)
    def rightAligned(self):
        return self._rightAligned

    @rightAligned.setter
    def rightAlignedSet(self, value):
        self._rightAligned = value
        self.rightAlignedChanged.emit()

    def paint(self, painter: QPainter):

        brush = QBrush(QColor("#007430"))

        painter.setBrush(brush)
        painter.setPen(Qt.NoPen)
        painter.setRenderHint(QPainter.Antialiasing)

        itemSize = self.size()

        painter.drawRoundedRect(0, 0, itemSize.width(), itemSize.height() - 10, 10, 10)

        if self.rightAligned:
            points = [
                QPointF(itemSize.width() - 10.0, itemSize.height() - 10.0),
                QPointF(itemSize.width() - 20.0, itemSize.height()),
                QPointF(itemSize.width() - 30.0, itemSize.height() - 10.0),
            ]
        else:
            points = [
                QPointF(10.0, itemSize.height() - 10.0),
                QPointF(20.0, itemSize.height()),
                QPointF(30.0, itemSize.height() - 10.0),
            ]
        painter.drawConvexPolygon(points)


if __name__ == "__main__":

    app = QApplication(sys.argv)
    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)
    qmlRegisterType(TextBalloon, "TextBalloonPlugin", 1, 0, "TextBalloon")
    view.setSource(QUrl.fromLocalFile("main.qml"))

    if view.status() == QQuickView.Error:
        sys.exit(-1)
    view.show()

    sys.exit(app.exec_())