Custom QQuickPaintedItem

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QQuickPaintedItem>
#include <QPainter>

class PaintedItem : public QQuickPaintedItem
{
    Q_OBJECT
    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged)

public:
    PaintedItem() {
    }

    void paint(QPainter *painter) override {
        painter->fillRect(0, 0, width(), height(), mColor);
    }

    QColor color() const {
        return mColor;
    }

    void setColor(const QColor &color) {
        if (color == mColor)
            return;

        mColor = color;
        update();
        emit colorChanged();
    }

signals:
    void colorChanged();

private:
    QColor mColor;
};

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qmlRegisterType<PaintedItem>("App", 1, 0, "PaintedItem");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

#include "main.moc"

main.qml

import QtQuick 2.7
import QtQuick.Window 2.0
import QtQuick.Controls 2.1

import App 1.0

ApplicationWindow {
    id: mainWindow
    x: Screen.width / 2 - width / 2
    y: Screen.height / 2 - height / 2
    width: 400
    height: 200
    visible: true

    Shortcut {
        sequence: "Ctrl+Q"
        onActivated: Qt.quit()
    }

    PaintedItem {
        width: 100
        height: 100
        color: "red"
    }
}