ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with arrays
for each (var item:Object in groupMap)
{
trace(item);
}
/* output:
[object Object]
[object Object]
[object Object]
*/
Object keys and memory management
Adobe® Flash® Player and Adobe® AIR use a garbage collection system to recover memory that is no longer used.
When an object has no references pointing to it, the object becomes eligible for garbage collection, and the memory is
recovered the next time the garbage collection system executes. For example, the following code creates a new object
and assigns a reference to the object to the variable myObject:
var myObject:Object = new Object();
As long as any reference to the object exists, the garbage collection system will not recover the memory that the object
occupies. If the value of myObject is changed such that it points to a different object or is set to the value null, the
memory occupied by the original object becomes eligible for garbage collection, but only if there are no other
references to the original object.
If you use myObject as a key in a Dictionary object, you are creating another reference to the original object. For
example, the following code creates two references to an object—the myObject variable, and the key in the myMap
object:
import flash.utils.Dictionary;
var myObject:Object = new Object();
var myMap:Dictionary = new Dictionary();
myMap[myObject] = "foo";
To make the object referenced by myObject eligible for garbage collection, you must remove all references to it. In this
case, you must change the value of myObject and delete the myObject key from myMap, as shown in the following code:
myObject = null;
delete myMap[myObject];
Alternatively, you can use the useWeakReference parameter of the Dictionary constructor to make all of the
dictionary keys weak references. The garbage collection system ignores weak references, which means that an object
that has only weak references is eligible for garbage collection. For example, in the following code, you do not need to
delete the myObject key from myMap in order to make the object eligible for garbage collection:
import flash.utils.Dictionary;
var myObject:Object = new Object();
var myMap:Dictionary = new Dictionary(true);
myMap[myObject] = "foo";
myObject = null; // Make object eligible for garbage collection.
Last updated 6/6/2012
40