QScriptEngine Class Reference
[QtScript module]

QScriptValue QScriptEngine::newFunction ( FunctionSignature fun, int length = 0 )

Creates a QScriptValue that wraps a native (C++) function. fun must be a C++ function with signature QScriptEngine::FunctionSignature. length is the number of arguments that fun expects; this becomes the length property of the created QScriptValue.

Note that length only gives an indication of the number of arguments that the function expects; an actual invocation of a function can include any number of arguments. You can check the argumentCount() of the QScriptContext associated with the invocation to determine the actual number of arguments passed.

A prototype property is automatically created for the resulting function object, to provide for the possibility that the function will be used as a constructor.

By combining newFunction() and the property flags QScriptValue::PropertyGetter and QScriptValue::PropertySetter, you can create script object properties that behave like normal properties in script code, but are in fact accessed through functions (analogous to how properties work in Qt's Property System). Example:

 static QScriptValue getSetFoo(QScriptContext *context, QScriptEngine *engine)
 {
     QScriptValue callee = context->callee();
     if (context->argumentCount() == 1) // writing?
         callee.setProperty("value", context->argument(0));
     return callee.property("value");
 }

 ....

 QScriptValue object = engine.newObject();
 object.setProperty("foo", engine.newFunction(getSetFoo),
     QScriptValue::PropertyGetter | QScriptValue::PropertySetter);

When the property foo of the script object is subsequently accessed in script code, getSetFoo() will be invoked to handle the access. In this particular case, we chose to store the "real" value of foo as a property of the accessor function itself; you are of course free to do whatever you like in this function.

In the above example, a single native function was used to handle both reads and writes to the property; the argument count is used to determine if we are handling a read or write. You can also use two separate functions; just specify the relevant flag (QScriptValue::PropertyGetter or QScriptValue::PropertySetter) when setting the property, e.g.:

 QScriptValue object = engine.newObject();
 object.setProperty("foo", engine.newFunction(getFoo), QScriptValue::PropertyGetter);
 object.setProperty("foo", engine.newFunction(setFoo), QScriptValue::PropertySetter);

See also QScriptValue::call().

QScriptValue QScriptEngine::newFunction ( FunctionSignature fun, const QScriptValue & prototype, int length = 0 )

Creates a constructor function from fun, with the given length. The prototype property of the resulting function is set to be the given prototype. The constructor property of prototype is set to be the resulting function.

When a function is called as a constructor (e.g. new Foo()), the `this' object associated with the function call is the new object that the function is expected to initialize; the prototype of this default constructed object will be the function's public prototype property. If you always want the function to behave as a constructor (e.g. Foo() should also create a new object), or if you need to create your own object rather than using the default `this' object, you should make sure that the prototype of your object is set correctly; either by setting it manually, or, when wrapping a custom type, by having registered the defaultPrototype() of that type. Example:

 QScriptValue Foo(QScriptContext *context, QScriptEngine *engine)
 {
     if (context->calledAsConstructor()) {
         // initialize the new object
         context->thisObject().setProperty("bar", ...);
         // ...
         // return a non-object value to indicate that the
         // thisObject() should be the result of the "new Foo()" expression
         return engine->undefinedValue();
     } else {
         // not called as "new Foo()", just "Foo()"
         // create our own object and return that one
         QScriptValue object = engine->newObject();
         object.setPrototype(context->callee().property("prototype"));
         object.setProperty("baz", ...);
         return object;
     }
 }

 ...

 QScriptValue fooProto = engine->newObject();
 fooProto.setProperty("whatever", ...);
 engine->globalObject().setProperty("Foo", engine->newFunction(Foo, fooProto));

To wrap a custom type and provide a constructor for it, you'd typically do something like this:

 class Bar { ... };

 Q_DECLARE_METATYPE(Bar)

 QScriptValue constructBar(QScriptContext *context, QScriptEngine *engine)
 {
     Bar bar;
     // initialize from arguments in context, if desired
     ...
     return engine->toScriptValue(bar);
 }

 class BarPrototype : public QObject, public QScriptable
 {
 // provide the scriptable interface of this type using slots and properties
 ...
 };

 ...

 // create and register the Bar prototype and constructor in the engine
 BarPrototype *barPrototypeObject = new BarPrototype(...);
 QScriptValue barProto = engine->newQObject(barPrototypeObject);
 engine->setDefaultPrototype(qMetaTypeId<Bar>, barProto);
 QScriptValue barCtor = engine->newFunction(constructBar, barProto);
 engine->globalObject().setProperty("Bar", barCtor);

 QScriptValue mySpecialQObjectConstructor(QScriptContext *context,
                                          QScriptEngine *engine)
 {
     QObject *parent = context->argument(0).toQObject();
     QObject *object = new QObject(parent);
     return engine->newQObject(object, QScriptEngine::ScriptOwnership);
 }

 ...

 QScriptValue ctor = engine.newFunction(mySpecialQObjectConstructor);
 QScriptValue metaObject = engine.newQMetaObject(&QObject::staticMetaObject, ctor);
 engine.globalObject().setProperty("QObject", metaObject);

 QScriptValue result = engine.evaluate("new QObject()");

 QScriptEngine engine;
 QScriptContext *context = engine.pushContext();
 context->activationObject().setProperty("myArg", 123);
 engine.evaluate("var tmp = myArg + 42");
 ...
 engine.popContext();

 Q_SCRIPT_DECLARE_QMETAOBJECT(QLineEdit, QWidget*)

 ...

 QScriptValue lineEditClass = engine.scriptValueFromQMetaObject<QLineEdit>();
 engine.globalObject().setProperty("QLineEdit", lineEditClass);

 struct MyStruct {
     int x;
     int y;
 };

 Q_DECLARE_METATYPE(MyStruct)

 QScriptValue toScriptValue(QScriptEngine *engine, const MyStruct &s)
 {
   QScriptValue obj = engine->newObject();
   obj.setProperty("x", s.x);
   obj.setProperty("y", s.y);
   return obj;
 }

 void fromScriptValue(const QScriptValue &obj, MyStruct &s)
 {
   s.x = obj.property("x").toInt32();
   s.y = obj.property("y").toInt32();
 }

 qScriptRegisterMetaType(engine, toScriptValue, fromScriptValue);

 MyStruct s = qscriptvalue_cast<MyStruct>(context->argument(0));
 ...
 MyStruct s2;
 s2.x = s.x + 10;
 s2.y = s.y + 20;
 QScriptValue v = engine->toScriptValue(s2);

 QScriptValue createMyStruct(QScriptContext *, QScriptEngine *engine)
 {
     MyStruct s;
     s.x = 123;
     s.y = 456;
     return engine->toScriptValue(s);
 }
 ...
 QScriptValue ctor = engine.newFunction(createMyStruct);
 engine.globalObject().setProperty("MyStruct", ctor);

 Q_DECLARE_METATYPE(QVector<int>)

 ...

 qScriptRegisterSequenceMetaType<QVector<int> >(engine);
 ...
 QVector<int> v = qscriptvalue_cast<QVector<int> >(engine->evaluate("[5, 1, 3, 2]"));
 qSort(v.begin(), v.end());
 QScriptValue a = engine->toScriptValue(v);
 qDebug() << a.toString(); // outputs "[1, 2, 3, 5]"