Signature for callback function used in signal_subscribe.
| connection | |
| sender_name |
The unique bus name of the sender of the signal. |
| object_path |
The object path that the signal was emitted on. |
| interface_name |
The name of the interface. |
| signal_name |
The name of the signal. |
| parameters |
A Variant tuple with parameters for the signal. |
| user_data |
User data passed when subscribing to the signal. |