Please help me in solving retain mystery in iPhone?

Question

Hello all,

Please consider the following code:

//CallerClass.h
@interface CallerClass : UITableViewController {

    NSMutableArray *dataArray;

}
@property(nonatomic,retain) NSMutableArray *dataArray;
-(void) setData;

//CallerClass.m
@implementation CallerClass
@synthesize dataArray;

-(id)initWithStyle:(UITableViewStyle)style {

    if (self = [super initWithStyle:style]) {
    [self setData];
   }
    return self;
}

-(void) setData
{
   dataArray = [CalledClass getData];
   [dataArray release];

}


//CalledClass.h
@interface CalledClass : NSObject {

}
+(NSMutableArray*) getData;

//CalledClass.m
@implementation CalledClass

+(NSMutableArray*) getData
{
   NSMutableArray* tempArray = [[NSMutableArray alloc] init];
   return tempArray;
}

I want to know what is the retain count for dataArray that is tempArray. Is it getting released. I dont want to use autorelease as I dont know till what time period I will need it. So I want to release it on my own. When I allocated tempArray, its retain count becomes 1. But when I assign it to instance variable dataArray whose property is retain, Is the retain count for that array becomes 2 or it stays 1. Like on releasing dataArray will it release memory.

Answer 1

dataArray = [CalledClass getData]; That doesn't invoke the retain attribute of the property. That's just plain old assignment iirc. [self setDataArray:[CalledClass getData]] would give a reference count of 2 on your array.

Answer 2

You've set up your property to retain the value, but then you're not using the accessor methods but set the instance variable directly instead:

dataArray = [CalledClass getData];

won't manage the retain count for you. You have to use:

self.dataArray = [CalledClass getData];

Also, in your CalledClass, I'd change the getData method to this:

+(NSMutableArray*) getData
{
   NSMutableArray* tempArray = [[NSMutableArray alloc] init];
   return [tempArray autorelease];
}

Normally I'd expect to get an autoreleased object back from a method with a name like this.

setData: should then be something like:

-(void) setData
{
   self.dataArray = [CalledClass getData];
}

or you could get rid of it entirely and just directly do

self.dataArray = [CalledClass getData]

in initWithStyle:.

By calling self.dataArray instead of assigning directly to the instance variable, your dataArray property will take care of retaining and releasing the object (because you specified "retain" in the property declaration)