What are QML FAQ in interviews?

Q) What is Qml ?
QML is the name of the language (just like C++, which is another language...)
QML stands for Qt Meta Language or Qt Modelling Language is a user interface markup language.
Q) How to call c++ call from QML?
QML call C + + methods with the Qt meta-object system. Like below:
onClicked: parent.color = parent.randomColor ()

Q) What are Four ways of integreting C++ with Qml?
Subclassing QQuickItem: QQuickItem allows you to write your own visual and non-visual QML items using C++.
Registering C++ types with QML: C++ classes can be registered with the QML type system, allowing them to be instantiated as QML types.
Registering Context Properties: QObjects can be registered with the QML context, allowing their properties to be directly accessed.
Accessing QML objects through the QML object tree: All QML objects reside in a tree hierarchy and can be accessed via the root of the tree.

Q) How to call a C++ function from a qml?
Through setcontext property.
Loading a main.qml with a simple Item as the root type through the QmlApplicationEngine will not show anything on your display, as it requires a window to manage a surface for rendering. The engine is capable of loading qml code which does not contain any user interface (e.g plain objects). Because of this it does not create a window for you by default.
The qmlscene or the new qml runtime will internally first check if the main qml file contains a window as a root item and if not create one for you and set the root item as a child to the newly created window.

Add callable methods using Q_INVOKABLE or Qt slots, and connect to Qt signals with an onSignal syntax

Q)How to call a QML function from c++?
QML functions can be called from C++ and vice-versa.
All QML functions are exposed to the meta-object system and can be called usingQMetaObject::invokeMethod(). Here is a C++ application that uses this to call a QML function:
// MyItem.qml
import QtQuick 1.0
Item {
    function myQmlFunction(msg) {
        console.log("Got message:", msg)
        return "some return value"
// main.cpp
QDeclarativeEngine engine;
QDeclarativeComponent component(&engine, "MyItem.qml");
QObject *object = component.create();
QVariant returnedValue;
QVariant msg = "Hello from C++";
QMetaObject::invokeMethod(object, "myQmlFunction",
        Q_RETURN_ARG(QVariant, returnedValue),
        Q_ARG(QVariant, msg));
qDebug() << "QML function returned:" << returnedValue.toString();
delete object;

Q)How to call a C++ function from QML ?
A C++ function can be called from a qml using set contextpropery in c++.
All QML signals are automatically available to C++, and can be connected to using QObject::connect() like any ordinary Qt C++ signal.
The signal is sent to QML, and the slot is invoked from QML.
There are different ways to send signals from C++ to QML and back. In this article, we show how to do this by embedding a C++ class directly into QML. This has the advantage that no Qt::connect connections need to be set-up manually.
In our example, we have a Receiver class that is implemented in C++.
This class defines a signal sendToQml and a slot receiveFromQml.
 Both have an integer parameter.
The signal is sent to QML, and the slot is invoked from QML.
QT += qml quick
#export QT_SELECT=5
SOURCES += main.cpp \
RESOURCES += qml.qrc
# Additional import path used to resolve QML modules in Qt Creator's code model
# Default rules for deployment.
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "receiver.h"
int main(int argc, char *argv[])
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    Receiver receiver;
    QQmlContext* ctx = engine.rootContext();
    ctx->setContextProperty("receiver", &receiver);
    //QDeclarativeView view;
    //sourcePath = "qrc:///DTC/qml/ITSDTC.qml";
    return app.exec();
#ifndef RECEIVER_H
#define RECEIVER_H
#include <QObject>
class Receiver : public QObject
    explicit Receiver(QObject *parent = 0);
    void sendToQml(int count);
public slots:
    void receiveFromQml(int count);
#endif // RECEIVER_H
#include "receiver.h"
#include <QDebug>
Receiver::Receiver(QObject *parent) :

void Receiver::receiveFromQml(int count) {
    qDebug() << "Received in C++ from QML:" << count;
import QtQuick 2.2
import QtQuick.Window 2.1
Window {
    id: test
    visible: true
    width: 200
    height: 50
    Connections {
        target: receiver
        onSendToQml: {
            console.log("Received in QML from C++: " + count)
    MouseArea {
        anchors.fill: parent
        onClicked: {

    Text {
        text: qsTr("Press me to send a signal to C++")
        anchors.centerIn: parent

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