this post was submitted on 03 Jul 2023
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Disconnecting a signal from inside the listener (programming.dev)
submitted 1 year ago* (last edited 1 year ago) by cook_pass_babtridge@programming.dev to c/godot@programming.dev
6 comments fedilink hide all child comments
 

Hi everyone, first time posting here. I was going to go to Discord but thought it's better to ask somewhere that can turn up on search engines for future confused game devs.

I've got a parameterised signal listener like this:

func _on_movement_to_exit_complete(character: Node2D):
	var f = func():
		print("_on_movement_to_exit_complete: "+str(character))
		var dungeon_tilemap: TileMap = dungeon_control.get_current_dungeon_tilemap()
		var party = dungeon_tilemap.get_node("Party")
		var initial_party = dungeon_control.get_parent().get_node("InitialParty")

		party.remove_child(character)
		initial_party.add_child(character)

		if party.get_child_count() == 0:
			for party_member in initial_party.get_children():
				var tilemap_movement: TilemapMovement = party_member.get_node("TilemapMovement")
				print("Disconnecting movement finished listener for "+str(party_member))
				tilemap_movement.disconnect("movement_finished", _on_movement_to_exit_complete(character))

			load_next_level()

	return f

Basically, if all the party members have exited the level (and been removed from the 'party' node) I want to disconnect this movement_finished signal from _on_movement_to_exit_complete. But when I try this I get an error:

E 0:00:07:0777   GameControl.gd:80 @ <anonymous lambda>(): Disconnecting nonexistent signal 'movement_finished', callable: <anonymous lambda>(lambda).
  <C++ Error>    Condition "!s->slot_map.has(*p_callable.get_base_comparator())" is true.
  <C++ Source>   core/object/object.cpp:1331 @ _disconnect()
  <Stack Trace>  GameControl.gd:80 @ <anonymous lambda>()
                 TilemapMovement.gd:23 @ _on_animation_finished()

Why doesn't it think movement_finished exists? Is there something wrong with disconnecting signals from inside their listeners? And is there another way of doing this? (Maybe something like a signal that fires once then disconnects?)

This is in Godot 4 by the way.

Also, is there a way to make the posting box wider in the programming.dev web frontend? It's really hard to work with pasted code here!

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[–] SLOMOBO 1 points 1 year ago

There are a couple of issues with this line:

tilemap_movement.disconnect("movement_finished", _on_movement_to_exit_complete(character))

Firstly, you're using the old Godot 3 API. You'll want to do this instead:

tilemap_movement.movement_finished.disconnect(_on_movement_to_exit_complete(character))

Secondly, the fact that you have parameterized anonymous functions as listeners makes things a little tricky. Let's say you call signal.connect() and pass a parameterized listener. Later, when you call signal.disconnect(), you have to pass it the same function. Calling _on_movement_exit_complete() with the same arguments returns a different (identical) function. There are a couple of ways you can work around this. A common solution would be to store your own references to the listeners for later use. something like this:

var movement_listeners = {}

func some_func_where_you_add_listeners():
    var character = # IDK, some reference to a character
    var listener = _on_movement_to_exit_complete(character)
    tilemap_movement.movement_finished.connect(listener)
    movement_listeners[character.name] = listener

func _on_movement_to_exit_complete(character: Node2D):
	var f = func():
		# ...
		if party.get_child_count() == 0:
			for party_member in initial_party.get_children():
                                # ....
                                var listener = movement_listeners[character.name]
				tilemap_movement.movement_finished.disconnect(listener)
                                movement_listeners.erase(character.name)

			load_next_level()

	return f

I hope that makes some sense