Hello Script Example▲

The Hello Script example shows the basic use of Qt Script: How to embed a script engine into the application, how to evaluate a script, and how to process the result of the evaluation. The example also shows how to apply internationalization to scripts.

 
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int main(int argc, char *argv[])
{
    Q_INIT_RESOURCE(helloscript);

The application will load the script file to evaluate from a resource, so we first make sure that the resource is initialized.

 
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    QApplication app(argc, argv);

    QScriptEngine engine;

    QTranslator translator;
    translator.load("helloscript_la");
    app.installTranslator(&translator);
    engine.installTranslatorFunctions();

We attempt to load a translation, and install translation functions in the script engine. How to produce a translation is explained later.

 
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    QPushButton button;
    QScriptValue scriptButton = engine.newQObject(&button);
    engine.globalObject().setProperty("button", scriptButton);

A push button is created and exported to the script environment as a global variable, button. Scripts will be able to access properties, signals and slots of the button as properties of the button script object; the script object acts as a proxy to the C++ button object.

 
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    QString fileName(":/helloscript.js");
    QFile scriptFile(fileName);
    scriptFile.open(QIODevice::ReadOnly);
    QTextStream stream(&scriptFile);
    QString contents = stream.readAll();
    scriptFile.close();

The contents of the script file are read.

 
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button.text = qsTr('Hello World!');
button.styleSheet = 'font-style: italic';
button.show();

The script sets the text (note that the qTr() function is used to allow for translation) and styleSheet properties of the button, and calls the button's show() slot.

 
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    QScriptValue result = engine.evaluate(contents, fileName);

The script is evaluated. Note that the file name is passed as the (optional) second parameter; this makes it possible for the script engine to produce a meaningful backtrace if something goes wrong, and makes the qTr() function be able to resolve the translations that are associated with this script.

 
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    if (result.isError()) {
        QMessageBox::critical(0, "Hello Script",
                              QString::fromLatin1("%0:%1: %2")
                              .arg(fileName)
                              .arg(result.property("lineNumber").toInt32())
                              .arg(result.toString()));
        return -1;
    }

If the result is an Error object (e.g. the script contained a syntax error, or tried to call a function that doesn't exist), we obtain the line number and string representation of the error and display it in a message box.

 
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    return app.exec();
}

If the evaluation went well, the application event loop is entered.

Translating the Application▲

The Qt Script internalization support builds on what Qt already provides for C++; see the Hello tr() Example for an introduction.

Since we haven't made the translation file helloscript_la.qm, the source text is shown when we run the application ("Hello world!").

To generate the translation file, run lupdate as follows:

 
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lupdate helloscript.js -ts helloscript_la.ts

You should now have a file helloscript_la.ts in the current directory. Run linguist to edit t