AIR - Call a method of different application and pass variable

Some time we need to trigger(call) a function of different application(parent) while an event occurs in child application. Lets say, we need to select an item from available item list. To select an item, a new window is created and it lists available items. The user selects an item. Once the user selected an item, it should be reflected in parent window.

I have created a function called changeItem() in ParentWindow. Since the function is triggered by an event, it should have a variable of type Event.
The code of the changeItem() is

public function changeItem(event:Event,inItem:String):void
{
/* variable inItem is passed by the ChildWindow */
txtSelectedItem.text=inItem;
}

(To create and call a window please see multiple windows in AIR )

Pass the application as a parameter.
When creating the instance of the ChildWindow in the ParentWindow, declare a variable of type ParentWindow and initialize to "this" i.e current application. The code is given here
declare variable
private var thisInstance:ParentWindow;

calling the ChildWindow
/*newChildWindow is of type ChildWindow*/
newChildWindow=new ChildWindow();
/* intialize the variable thisInstance in init() function if you are referring the intansce in multiple places*/
thisInstance=this;
newChildWindow.parentWindowInstance=thisInstance;
newChildWindow.open();

In the ChildWindow (select item window), add a listener to the select button/component and call the function of the Parent window (changeItem).

add event listener function
cmd.addEventListener(MouseEvent.CLICK, function(e:MouseEvent):void
{
/* parentWindowInstance variable is the instance of the ParentWindow and it is initialized by the ParentWindow when the instance of the ChildWindow is created
parentWindowInstance is declared in ChildWindow <Script> section */
parentWindowInstance.changeItem(e,pTxtInput.text);
}
here, a function is declared in the parameter place. This declaration acts as parameter passing trick.