Hello Script Example

Files:

• script/helloscript/helloscript.js
• script/helloscript/main.cpp
• script/helloscript/helloscript.pro
• script/helloscript/helloscript.qrc

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.

 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.

     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.

     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.

     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.

 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.

     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.

     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.

     return app.exec();
 }

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

 lupdate helloscript.js -ts helloscript_la.ts

 linguist helloscript_la.ts

 <translation type='unfinished'></translation>

 <translation>Orbis, te saluto!</translation>