I have a question how can I clear/free memory in flash? For example I am finishing game and I want to start from beginning and if I will just jump to the first frame all the objects there are still in this memory, is any possibility to force cleaning memory?
Can I free memory for an object? for example I removeChild(something) - and I want to free memory for an object as I will reuse it?
Can anybody explain me how the engine works?
Thanks
I would encourage you to read Chapter 14, Garbage Collection in the "Moock Book" (Essential ActionScript 3.0 by O'Reilly Publishing).
The short answer to your question is that you're not in control of de-allocation, the garbage collector is. In a garbage-collected language like AS3 or Java, you don't have manual control over allocation and de-allocation of memory like you do in lower level languages; there are no AS3 equivalents to things like delete in C++ or free in C. Your goal should not be controlling when you destroy things, but rather not forgetting to remove references to things you no longer need around and making sure you disable things that you intend for garbage collection.
Memory leaks in AS3 typically come from a mixture of newbie misunderstanding (like thinking removeChild or setting a reference to null destroys objects), and from not keeping good track of references to objects--especially where strong listeners are involved.
A previous respondent posted this:
myObject = null;
What this does is remove a reference to the object that the variable myObject was holding. Nothing more. You need to know a lot more about the situation in order to be able to say whether this assignment even makes the object in question eligible for garbage collection, especially how many other variable are holding references to the object. And the object might already be eligible for garbage collection even if you didn't set the reference to null (i.e. if myObject has no connection to a GC root).
Suffice to say, the entire GC mechanism is more complex than can be satisfactorily explained in a StackOverflow post. That's why it has a whole chapter in the Moock Book, and even that book does not go into implemenation detail or great detail about when exactly the Flash Player does its ref counting deletions or mark and sweep passes.
The most important things to remember are, IMHO:
When you intend to "kill" an object, give it a cleanUp() or destroy() function where you do things like stop all its timers, sounds, remove listeners, etc. An object will continue to exist and execute code until it gets GC'd. And the Flash Player defers GC as long as it can--it's usually triggered when the Player needs to allocate more RAM from your system, because allocating memory is about the only thing that's more time consuming than doing the mark and sweep GC pass.
Read about weak vs strong listeners. Basically, when you have a weak listener, the listener reference is one that is ignored by mark-and-sweep GC, so it alone will not prevent an object from getting collected. But don't listen to anyone who tells you "always use weak" or "always use strong listeners and manually remove them" because there are times where each is appropriate, and that's why the choice is yours.