Signal handlers

GObject signals

Signals are very useful object oriented mechanism to react to events and propagate information between objects. A Class declares signal names and signatures which can be emitted by its instance. Using connect method on an object one can connect a signal handler to id. A signal handler is a function or method which is called each time the signal is emitted. Some signals are emitted automatically by application event, all of them can be emitted by emit method.

Signals in JSON

ClutterScript allows specifying signal handlers in JSON. To do this use signals key, which value has following form:

{
    "id": "some_object",
    "type": "SomeType",
    "signals": [
        {
            "name": "signal-name",
            "handler": "handler_name",
            "object": "optional_object_id"
        }
    ]
}

For each handler there are 3 parameters:

• name - signal name as in class declaration
• handler - name of the handler,
• object - optional object id or dictionary with declaration.

Handler names are dependent on script loader implementation. In Pisak there is custom handler loader which has its own lookup dictionary. pisak.signals module has functions to register and resolve handler names. Many useful handlers are declares in pisak.handlers module.

object parameter is optional, not using it is equivalent to setting it to signal emitter. The downside of connecting signal handlers in JSON is that there is no local scope for handler to operate in. Then only object available to the handler is the one specified by object key.