Returns whether there are any handlers connected to
instance for the given signal id and detail.
detail is 0 then it will only match handlers that were connected without detail. If
detail is non-zero then it
will match handlers connected both without detail and with the given detail. This is consistent with how a signal emitted with
would be delivered to those handlers.
Since 2.46 this also checks for a non-default class closure being installed, as this is basically always what you want.
One example of when you might use this is when the arguments to the signal are difficult to compute. A class implementor may opt to not emit the signal if no one is attached anyway, thus saving the cost of building the arguments.
the object whose signal handlers are sought.
the signal id.
whether blocked handlers should count as match.
true if a handler is connected to the signal, false otherwise.