How to call c++ function from qml and change the lable text

Question

I'm new to Blackberry 10 development. I've created simple BB 10 cascades project. I want to change the text of a label through c++ function.

main.qml

      import bb.cascades 1.0    
      Page {
         content: Container {
         id: containerID
         Button {
            id: button1
            objectName: "button"
            text: "text"
            onClicked: {
                btnClicked("New Label Text");
            }
        }
        Label {
            id: label1
            objectName: "label1"
            text: "Old Label Text"
        }
    }
}

Now in which file i've to declare and in which file i've to define the function btnClicked(QString) function.

HelloBB.hpp

// Default empty project template
#ifndef HelloBB_HPP_
#define HelloBB_HPP_

#include <QObject>

namespace bb { namespace cascades { class Application; }}

class HelloBB : public QObject
{
    Q_OBJECT
    public:
    HelloBB(bb::cascades::Application *app);

    virtual ~HelloBB() {}

};

#endif

HelloBB.cpp

// Default empty project template
#include "HelloBB.hpp"
#include <bb/cascades/Application>
#include <bb/cascades/QmlDocument>
#include <bb/cascades/AbstractPane>

using namespace bb::cascades;
HelloBB::HelloBB(bb::cascades::Application *app) : QObject(app)
{
    // create scene document from main.qml asset
    //set parent to created document to ensure it exists for the whole application lifetime
    QmlDocument *qml = QmlDocument::create("asset:///main.qml").parent(this);

    qml->setContextProperty("app", this);

    // create root object for the UI
    AbstractPane *root = qml->createRootObject<AbstractPane>();

    // set created root object as a scene
    app->setScene(root);
}

Now I want to change the label text from Old Label Text to the user given text. I'm calling the c++ function from qml. I don't know where to define this function and how to connect this c++ function from qml.

Thanks.

Answer 1

You can find the documentation for integrating C++ and QML here: http://developer.blackberry.com/cascades/documentation/dev/integrating_cpp_qml/

As a cliff's notes:

In your HelloBB constructor you can expose the class to the QML like so:

    qml->setContextProperty("HelloBB", this);

And then create a method in the C++ that you will be able to call from the QML. Remember, the method has to be marked as Q_INVOKABLE to be called from the QML.

Consider this:

        In HelloBB.hpp:

    public:
           Q_INVOKABLE void test();

        In HelloBB.cpp:

    void HelloBB::test() {
        qDebug() << "TEST";
    }

        In main.qml:

   onClicked: {
       HelloBB.test ()
   }