The autoreleasepool with ARC in iOS - ios

Question

In iOS, when the autoreleasepool create and be destroyed?
When a touch event created, the runloop create an autoreleasepool.
When the touch event ends, the autoreleasepool will be destroyed.
Is my understand of the autoreleasepool right?
#import <UIKit/UIKit.h>
#import "AppDelegate.h"
int main(int argc, char * argv[]) {
#autoreleasepool {
return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
}
}
how can I understand the autoreleasepool in main method?

Answer 1

In xcode 4 we have to create pool and we have release it by using this syntax with NSAutorealeasePool:
{
NSAutorealeasePool *pool=[[NSAutorealeasePool alloc] init];
[pool drain];
}
When ever use like this in Xcode 4 memory is initialized for your pool and control enter into your pool deallocate your pool objects by using drain ..if u use drain means u permanently destroy ypur pool objects..if you use release means its not completely destroyed..
In xcode 5 we are using #autoreleasepool syntax like this:
#autoreleasepool
{
}
Here we don't need to create pool and release the objects..every thing done by compiler..once control enters automatically create the pool and release the pool objects means which we want to deallocate

Answer 2

The NSAutoreleasePool class is used to support Cocoa’s reference-counted memory management system. An autorelease pool stores objects that are sent a release message when the pool itself is drained.
IMPORTANT
If you use Automatic Reference Counting (ARC), you cannot use autorelease pools directly. Instead, you use #autoreleasepool blocks. For example, in place of:
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// Code benefitting from a local autorelease pool.
[pool release];
you would write:
#autoreleasepool {
// Code benefitting from a local autorelease pool.
}
#autoreleasepool blocks are more efficient than using an instance of NSAutoreleasePool directly; you can also use them even if you do not use ARC.
Few things to keep in mind -
Case 1)
#autoreleasepool
{
MyObject *obj = [[MyObject alloc] init];
//No need to do anything once the obj variable is out of scope there are no strong pointers so the memory will free
}
case 2)
MyObject *obj //strong pointer from elsewhere in scope
#autoreleasepool
{
obj = [[MyObject alloc] init];
//Not freed still has a strong pointer
}