Question

When a method returns an object that is taken from and NSMutableArray does the object must be autoreleased? Check the following method. Also should I autorelease the nil value?

-(NSObject*)getElementByID:(NSString*)ID{

    for(int i=0;i<[elements count];i++){
        NSObject *element = (NSObject*) [elements objectAtIndex:i];

        if([element.key isEqualToString:ID]){
            return [element autorelease];
        }
    }

    return nil;
}

Answer 1

You must not autorelease element because you are not an owner of it (you have not put a retain on it). You would have become an owner of it if you acquired it using alloc, new or retain. Since you acquired this object calling objectAtIndex:, you do not own it. See Three Magic Words. Calling autorelease here will cause a crash later do to over-release.

Your method name is incorrect and breaks KVC. A method that begins with get must take a pointer that will be updated with the result. This should be elementForID:. As noted above with the three magic words, naming in ObjC is very important to writing stable code

As a side note, it is traditional to use id is most cases rather than NSObject*. They mean slightly different things, but typically id is correct.