Question

Let’s say there is a buttonView ( ie. a simple button) . To register a click in my rootView , i do as follows :

generally followed 1st Approach :
class RootView
{
var buttonView:ButtonView ;
….
buttonView.addEventListener( ButtonView.CLICK, buttonView_click ) ;
…
}

I wonder, why not a basic approach ( 2nd Approach ) is followed like this :

class RootView 
{
   var buttonView:ButtonView ; 
   buttonView.setFunction( buttonView_click ) ;

}


class ButtonView()
{
    public function setFunction(  someFunction:Function)
    {
        viewFunctionArray_Arr.push( someFunction ) 
    }

    public function onClick()
    {
        // remove dispatchEvent from here , instead 

        for ( var i=0; i< viewFunctionArray_Arr.length; i++)
        {
            //calling the registered functions of all the views one by one
            viewFunctionArray_Arr[i] ( ) ; 
        }

    }


}

If the explanation is regarding “Loose Coupling”, then i wonder, how “1st approach” is loose coupling, because afterall in the 1st approach, we are using instance “buttonView” in the views that need it. So rootView needs to know about buttonView. Isn’t it ?

Answer 1

When you use addEventListener() Flash player is doing something very similar to your second approach.

One reason I would use addEventListener() instead of passing a reference to a function is to avoid potential memory leaks:

addEventListener() has some optional parameters. The last one specifies to use a weak reference: addEventListener(MouseEvent.CLICK, eventHandler, false, 0, true). Weak references do not prevent an object from getting garbage collected.

There are cases when an object is disposed that you need to clean up things (ie: remove event listeners), and using a weak reference can mitigate some of the clean up tasks.

In regards to loose coupling, I think both approaches are the same. In one case the parent object needs to know that the child view dispatches an event. In the other, the parent needs to know that it should pass an event handling function to the view. These are both loosely coupled in my opinion, there is nothing stopping you from using the child view somewhere else.