NSMutableArray and memory managment

I am learning Objective C coming from a language which has garbage collection and I am struggling with memory management. In particular I am struggling with what happens in this instance.

// Global variable
NSMutableArray *parentArray;

// Instance
- (void)testing {
  parentArray = [[NSMutableArray alloc] init]; 
  NSMutableArray *childArray = [[NSMutableArray alloc] init];

  [childArray addObject:@"mike"];
  [parentArray addObject:childArray];
}

childArray开发者_如何学Go is a pointer to an array so when I addObject it to the parentArray does it copy it or pass the pointer? If, like I think, it passes the pointer I can't [childArray release] in this method as it would destroy the object and I wouldn't be able to read from it elsewhere.

Therefore do I have to release it in the main dealloc method at the end of the class?

Any help greatly appreicated as I'm struggling.

Mike

You can release the childArray in the same function, because NSMutableArray retains all the added object.

NSMutableArray (and all other standard objective-c containers) retain objects added to them, so you can release your childArray right after it was added to parentArray.

Moreover immediate release will improve your code readability - as it is clear that object ownership passes to the parentArray.

when you add childArray to the parentArray it is retained once. So, in that point you will have 2 like value in the retain count. Therefore, you can easily release childArray in the method (testing) and keep a reference within the parentArray (retain count = 1). It won't be destroyed then.

Just add the "autorelease" in the childArray declaration, so that array will be released when possible (childArray so will be released when you release the parentArray that owns that child).

// Global variable
NSMutableArray *parentArray;

// Instance
- (void)testing {
  parentArray = [[NSMutableArray alloc] init]; 
  NSMutableArray *childArray = [[[NSMutableArray alloc] init] autorelease];

  [childArray addObject:@"mike"];
  [parentArray addObject:childArray];
}

- (void) dealloc {
   [parentArray release];
}

addObject: just add object pointer,and retain the object which is added. when removeObject: the array remove the item(pointer),and item will receive the release message.

• when you NSMutableArray *childArray = [[NSMutableArray alloc] init]; the childArray retainCount is 1.
• when you [parentArray addObject:childArray]; the childArray retainCount is 2.

when retainCount is 0, and memory not enough, the object will be destroy.

there is same code:

NSMutableArray *parentArray;

parentArray = [[NSMutableArray alloc] init]; 
NSMutableArray *childArray = [[NSMutableArray alloc] init];
NSLog(@"1.childArray retainCount:%d",[childArray retainCount]);
[childArray addObject:@"mike"];
NSLog(@"2.childArray retainCount:%d",[childArray retainCount]);
[parentArray addObject:childArray];
NSLog(@"3.childArray retainCount:%d",[childArray retainCount]);
[parentArray removeAllObjects];
NSLog(@"4.childArray retainCount:%d",[childArray retainCount]);

result:

1.childArray retainCount:1
2.childArray retainCount:1
3.childArray retainCount:2
4.childArray retainCount:1

try it,know it.