Access QML Element properties from C++

Qt provides various method for working with QML. This following tutorial shows, how a QML Element properties can be accessed and modified from C++ code using QDeclarativeProperty class.

It will show a simple idea on accessing properties which cannot be accessed directly.

main.qml

import QtQuick 1.1

Rectangle {
    id: parentRect
    property bool layoutValue : LayoutMirroring.enabled ? true : false;// Read Only
    LayoutMirroring.enabled: false
    LayoutMirroring.childrenInherit: true
    width: 300; height: 50
    color: "yellow"
    border.width: 1

    Row {
        anchors { left: parent.left; margins: 5 }
        y: 5; spacing: 5

        Repeater {
            model: 5

            Rectangle {
                color: "red"
                opacity: (5 - index) / 5
                width: 40; height: 40

                Text {
                    text: index + 1
                    anchors.centerIn: parent
                }
            }
        }
    }
}

main.cpp

#include 
#include 
#include 
#include 
#include "qmlapplicationviewer.h"

Q_DECL_EXPORT int main(int argc, char *argv[])
{
    QScopedPointer app(createApplication(argc, argv));
    QScopedPointer viewer(QmlApplicationViewer::create());

    viewer->setOrientation(QmlApplicationViewer::ScreenOrientationAuto);
    viewer->setMainQmlFile(QLatin1String("qml/Test/main.qml"));
    QDeclarativeProperty propLayout(viewer->rootObject(),"layoutValue");
    QDeclarativeProperty propLayoutMargin(viewer->rootObject(),"anchors.leftMargin");

    qDebug() << "Layout Property :" << propLayout.read().toBool();
    qDebug() << "Layout Margin :" << propLayoutMargin.read().toReal();

    qDebug() << "Property Modified? " << propLayoutMargin.write(QVariant::fromValue(20));
    if(propLayout.type() == QDeclarativeProperty::Invalid)
        qDebug() << "Invalid Layout Mirror property";
    if(propLayoutMargin.type() == QDeclarativeProperty::Invalid)
        qDebug() << "Invalid Anchor Margin property";
    viewer->showExpanded();

    return app->exec();
} 

Qt for Android - __atomic_inc undefined error!

I have also encountered this error. This is how I rectified.

Select Projects on the left panel (below Debug). Select "Build" in the top and make sure the Qt Version and arm configuration are same in
1) Compilation Target (Android robot symbol)
2) Edit Build Configuration (drop down list box)
3) Qt Version (General category)

Now click "Run" next to "Build". Now select atleast "android-8" as the Android target. Now clean the project and click rebuild. This should clear this error.