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=======
Signals
=======
GObject signals are a system for registering callbacks for specific events.
To find all signals of a class you can use the
:func:`GObject.signal_list_names` function:
.. code:: pycon
>>> GObject.signal_list_names(Gio.Application)
('activate', 'startup', 'shutdown', 'open', 'command-line', 'handle-local-options')
>>>
To connect to a signal, use :meth:`GObject.Object.connect`:
.. code:: pycon
>>> app = Gio.Application()
>>> def on_activate(instance):
... print("Activated:", instance)
...
>>> app.connect("activate", on_activate)
17L
>>> app.run()
('Activated:', <Gio.Application object at 0x7f1bbb304320 (GApplication at 0x5630f1faf200)>)
0
>>>
It returns number which identifies the connection during its lifetime and which
can be used to modify the connection.
For example it can be used to temporarily ignore signal emissions using
:meth:`GObject.Object.handler_block`:
.. code:: pycon
>>> app = Gio.Application(application_id="foo.bar")
>>> def on_change(*args):
... print(args)
...
>>> c = app.connect("notify::application-id", on_change)
>>> app.props.application_id = "foo.bar"
(<Gio.Application object at 0x7f1bbb304550 (GApplication at 0x5630f1faf2b0)>, <GParamString 'application-id'>)
>>> with app.handler_block(c):
... app.props.application_id = "no.change"
...
>>> app.props.application_id = "change.again"
(<Gio.Application object at 0x7f1bbb304550 (GApplication at 0x5630f1faf2b0)>, <GParamString 'application-id'>)
>>>
You can define your own signals using the :obj:`GObject.Signal` decorator:
.. function:: GObject.Signal(name='', flags=GObject.SignalFlags.RUN_FIRST, \
return_type=None, arg_types=None, accumulator=None, accu_data=None)
:param str name: The signal name
:param GObject.SignalFlags flags: Signal flags
:param GObject.GType return_type: Return type
:param list arg_types: List of :class:`GObject.GType` argument types
:param accumulator: Accumulator function
:type accumulator: :obj:`GObject.SignalAccumulator`
:param object accu_data: User data for the accumulator
.. code:: python
class MyClass(GObject.Object):
@GObject.Signal(flags=GObject.SignalFlags.RUN_LAST, return_type=bool,
arg_types=(object,),
accumulator=GObject.signal_accumulator_true_handled)
def test(self, *args):
print("Handler", args)
@GObject.Signal
def noarg_signal(self):
print("noarg_signal")
instance = MyClass()
def test_callback(inst, obj):
print "Handled", inst, obj
return True
instance.connect("test", test_callback)
instance.emit("test", object())
instance.emit("noarg_signal")
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