CODEWITHSUNDEEP
javascriptqtqt5
MaksymB
MaksymB

Reputation: 1307

Qt 5.0: Exposing C++ methods to Java Script

I try to expose an object as a global property to Java Script which has the method below:

Q_INVOKABLE MyObject* createMyObject();

MyObject is derived from QObject.

when I call this method in Java Script it returns an object of type:

QVariant(MyObject*)

I'm wondering if it's possible to automatically convert it to QJSValue so I can use it further in the script?

Upvotes: 6

Views: 4189

Answers (4)

Buggy
Buggy

Reputation: 1

I am in a similar situation, trying to use QJSEngine for scripting (at the moment stuck at trying to expose a QList to QJSEngine...)

I think the easiest way to expose an existing C++ object to scripting is like so:

//create c++ file object
MyObject* anObject = new MyObject();

//make c++ object available to script
QJSValue scriptObject = myEngine.newQObject(anObject);
myEngine.globalObject().setProperty("obj", scriptObject);

You should now be able to access "obj" from script.

By the way, how to you find out the type in script (QVariant(MyObject*))?

Upvotes: 0

MaksymB
MaksymB

Reputation: 1307

All that needs to be done is calling the method below somewhere before referencing MyObject in the script.

qmlRegisterType<MyObject>("", 1, 0, "MyObject");

Then createMyObject method will return correct type without any conversion:

var obj = createMyObject();

MyObject

Actually if we change type of the method below

Q_INVOKABLE MyObject* createMyObject();

to

Q_INVOKABLE QObject* createMyObject();

it will start working even without

qmlRegisterType

Upvotes: 3

MaksymB
MaksymB

Reputation: 1307

Seems that Java Script uses QVariant as an opaque wrapper around any 'unknown' type. The value can be passed around easily but non of its properties can be used and non of its methods can be invoked. To be used in script it should be converted to QJSValue. The only way I found is declaring helper function like this:

Q_INVOKABLE QJSValue convert(QVariant var)
{
    return _engine.newQObject(var.value<QObject*>());
}

then it's possible to convert QVariant to QJSValue:

var obj = convert(createMyObject());

and obj will be of type

MyObject

So now it can be used in script.

Upvotes: 4

Alexander Stepaniuk
Alexander Stepaniuk

Reputation: 6408

You can use QJSEngine::newQObject() method.

Use newQObject() to wrap a QObject (or subclass) pointer. newQObject() returns a proxy script object; properties, children, and signals and slots of the QObject are available as properties of the proxy object. No binding code is needed because it is done dynamically using the Qt meta object system.

Please read further details at QJSEngine Class: QObject Integration.

Upvotes: 2

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