Memory management : release viewcontroller object after adding to NSMutableArray

Question

I have a memory leak with below code. If I use [sub release]; after adding sub to NSmutableArray(subViewController), Analyzer says "Inconrrect decrement of the reference count of an object that is not owned at this point by the caller" , when i remove [sub release] then it says "Potential leak of an object allocated on xx line"

for (int i=0; i<[self.data count]; i++) {

   SubCategoryViewController *sub =[[SubCategoryViewController alloc] 
           initwithServiceUrl:urlString andHeaderValue: 
          ((PMCategory *)[self.data objectAtIndex:i]).categoryName];

   [[AppDelegate sharedAppDelegate].viewController.subViewControllers addObject:sub];
   [sub release];


}

Alson if I use autorelease Warning becomes "Object sent -autorelease too many times"

SubCategoryViewController *sub =[[[SubCategoryViewController alloc] 
           initwithServiceUrl:urlString andHeaderValue: 
          ((PMCategory *)[self.data objectAtIndex:i]).categoryName]autorelease];

Added from comment: SubCategoryViewController Init method:

@property (nonatomic, retain) NSMutableArray *data;
@property (nonatomic, copy) NSString *headerText;
@synthesize data = _data;
@synthesize headerText=_headerText;

...

self = [super init];
if (self) {
    self.data = [[NSMutableArray alloc] init] ;
    self.headerText =headerValue;
    self.serviceURL =serviceU;
    self.firstLoad = YES;
}
return self;

Answer 1

it is because you haven't followed proper naming convention of Objective c. Whenever you are writing any initialization function namingConvention is something like

-(id) initFirstWordSecondWord{
}

means make first letter after init Capital.

So change your initwithServiceUrl to initWithServiceUrl and your problem will be solved. cheer up!!!

Answer 2

If data is a property with the retain attribute then it is over retained, once by:

[[NSMutableArray alloc] init]

and once by the property setter.

Change it to use the class convenience method that returns an autoreleased NSMutableArray :

self.data = [NSMutableArray array];

Additionally the for loop can be written more clearly with fast enumeration:

for (PMCategory *category in self.data) {
    SubCategoryViewController *sub =[[SubCategoryViewController alloc] 
        initwithServiceUrl:urlString
        andHeaderValue:category.categoryName];