Question

Object A calls method M of object B, passing it two callbacks for two cases: cbYes and cbNo.

B, in turn, performs a web service async call, creating Object C (api) instance with the only callback: method N of B. This callback will decide which of the two callbacks to call.

I store cbYes and cbNo functions as B’s private vars of type Function.

How can I call either callback? They’re not children of B, so syntax B[cbYes](); is not the way. Unreal code example:

class A {
    public function Smth() {
        var instB:B = new B( cbYes, cbNo);
    }
    public function cbYes( e:Event) { doSomething(); }
    public function cbNo( e:Event) { doSomething(); }
}

class B {
    private var _cb1:Function;
    private var _cb2:Function;
    public function B( cb1, cb2) {
        _cb1 = cb1; _cb2 = cb2;
        var worker:C = new C();
        C.apiMethod123( cbAfterCall);
    }
    public function cbAfterCall( Result:*) {
        if( Result = 1) {
            // here I need to call callback from _cb1
        } else {
            // here I need to call callback from _cb2
        }
    }
}

class C {
    private var _Callback:Function;
    public function C() { }
    public function apiMethod123( cb:Function) {
        this._Callback = cb;
        // create a URLLoader or a Loader and do a web service call
    }
    public function urlCallback( e:Event) {
        // parse response
        this._Callback();
    }
}

Ok, while I was putting together this sample code, I realised I already solved this with the api caller worker! 🙂 Got to have more sleep.

AfterQuestion: does this architectural approach seems really wrong? Please advice a better one, or a pattern that suits the system where concurrent asynchronous API calls are used.

Answer 1

If you store cbYes and cbNo as member variables inside B. You can call them like normal functions:

public function foo(cbYes:Function,cbNo:Function):void
{
    this.cbYes = cbYes;
    this.cbNo = cbNo;
}

public function bar():void
{
    cbYes();
}

Instead of using callbacks like this you can use the event system to achieve the same result. You can create custom events and dispatch the yes/no event.