Reading and writing files in QML (Qt)

Question

I am trying to implement Reading and writing files in QML and came across the linked article from Nokia but have not been able to successfully use the seemingly obvious code

Answer 1

The example written by Nokia in the tutorial is not a pure QML program. It contains both C++ and QML. This kind of program is usually a C++ program which loads a QML file and renders it. C++ programs usually begin with a function called int main(int argc, char *argv[]);. In your case, it is this "main()" function which loads your QML main file (main.qml) file and renders it.

But before loading the QML main file, you have to tell the QML system that you will use a custom QML class called FileIO. For this, you will have to use the int qmlRegisterType(const char * package, int majorVersion, int minorVersion, char * classNameInQML); C++ function. It takes about 5 parameters :

• T : the C++ template parameter. It is your C++ class (FileIO).
• package : all QML classes are in package which are versionned. This is the name of the package.
• majorVersion : all QML classes are in package which are versionned. This is the major version number of the package.
• minorVersion : all QML classes are in package which are versionned. This is the minor version number of the package.
• classNameInQML : all QML classes are in package which are versionned. This is the name of your class that you will use in QML files Most of the time the name is the same than the C++ class name.

For using this function, you have to include a C++ header in the C++ file where you write it :

• If you use Qt 4, the header is .
• If you use Qt 5, the header is .

In the end you should have some stuff like this :

main.cpp (file with the main() C++ function) :

// C++ header to include for using qmlRegisterType();
#include     // If you use Qt4
#include             // If you use Qt5

// Some stuff used by the main(); function
#include 
#include 

#include "ui/qtquickapplicationviewer.hpp"    // Something which manages your QML files. Qt Creator will generate it for you if you use it to code..
#include "fileio.h"    // Your FileIO C++ class

/**
 * @fn Q_DECL_EXPORT int main(int argc, char *argv[])
 * @brief The C++ main(); function. Your program begins HERE.
 */
Q_DECL_EXPORT int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    // ...

    // Declaring your C++ class to the QML system
    qmlRegisterType("MyCustomClasses", 1, 0, "FileIOQML");

    // ...

    // Loading your main QML file
    QLatin1String mainQMLFile = "./ui/qml/main.qml";
    QtQuickApplicationViewer viewer;
    viewer.setMainQmlFile(mainQMLFile);

    // Showing how beautiful your QML interface is :)
    viewer.showExpanded();

    // Now let's play with your QML interface is :)
    return app.exec();
}

main.qml file to load (right from the Nokia tutorial) :

import QtQuick 1.1
import MyCustomClasses 1.0

Rectangle {
    width: 360
    height: 360
    Text {
        id: myText
        text: "Hello World"
        anchors.centerIn: parent
    }

    FileIOQML {
        id: myFile
        source: "my_file.txt"
        onError: console.log(msg)
    }

    Component.onCompleted: {
        console.log( "WRITE"+ myFile.write("TEST"));
        myText.text =  myFile.read();
    }
}

NB : I have changed some "FileIO" from the Nokia tutorial in order to avoid confusions.