HaxeFlixel Signals

I really like the signal API from AS3 and use it all the time. I even ported it to Swift, JS and Dart in order to apply it in other environments. To use signals in HaxeFlixel you just need to define an object, that will represents your signal, and its callback type. So, for example, if you want to make a signal, that will need one String, you have to create a signal like that:

var signal = new FlxTypedSignal<String->Void>();

To use it you need to call dispatch method:

signal.dispatch("Hi");

In order to receive this message you need to add a listener (callback). Signal’s listener is a function that will be triggered, when method dispatch is called. Signature of a callback and a signal’s signature must be equal. So if you created a signal, that sends 1 String, you need a callback, that will accept 1 String. A callback for the previous signal will be:

function someListener(id:String):Void{}

There are 2 possibilities to add a listener to a signal. You can attach it permanently using code

signal.add(someListener);

or you can add it only for a one trigger using a function

signal.addOnce(someListener);

Method addOnce is a shortcut for the removing a listener after the first received message.

To remove a listener from a signal you need to use

signal.remove(someListener);

Alternatively you can remove all listeners from a signal by calling method removeAll().

In order to add more parameters to your signal, you can add them in the signature. For example, this signal will send a String and an object of type Dynamic

var signal = new FlxTypedSignal<String->Dynamic->Void>();

You can also create a signal without parameters by using shortcut class:

var signal = new FlxSignal();

It works exactly like FlxTypedSignal, just without any parameters.

As all other HaxeFlixel objects you can destroy a signal using

signal = FlxDestroyUtil.destroy(signal);

if it is not needed anymore.

P.S At the moment (Version 3.3.12) FlxDestroyUtil.destroy doesn’t work on signals (see more here), also a manual way doesn’t work

if(signal!=null)
{
  signal.destroy();
  signal=null;
}

so you have to remove your listeners using a method removeAll(), if you don’t need them anymore.

More information about HaxeFlixel Signals you can find on Cheat Sheet, documentation or in source.

One side note, if you are new to Signals. Compared to events, signals are dispatched synchrony, that means your callbacks will be trigged instantly after dispatch() is called. Take it into account, as you can get some very wild behaviors, if you use signals improperly.

Happy coding :)