Memory Management in Objective-C when dealing with NSMutableArray

Question

Hi Guys , In Instruments the tempPlayer object is showing a leak. In this code, in every for loop I keep on allocating a new tempPlayer instance, set its playerCode variable with a string and add it to an NSMutableArray in each iteration. Instruments shows me a leak in the alloc statement. Is there any way to prevent tat leak in the tempPlayer object ?

 for(int i = 0 ; i < [homeLineupArray count] ; i++) {   
    NSArray * tildeSeperator = [[homeLineupArray objectAtIndex:i] componentsSeparatedByString:@"~"];

    [self.tempPlayer release];
    self.tempPlayer = [[LineUpsPlayer alloc] init];
    tempPlayer.playerCode = [tildeSeperator objectAtIndex:0];

    [matchLineUp.homeTeamPlayingEleven addObject:tempPlayer ];
}

Thanks Harikant Jammi

Answer 1

Things may depend on how do you declare your tempPlayer property in your class (and as it looks that it is temporary object, consider do you need a property accessor for it?)

for(int i = 0 ; i < [homeLineupArray count] ; i++) {   
    NSArray * tildeSeperator = [[homeLineupArray objectAtIndex:i] componentsSeparatedByString:@"~"];

    [self.tempPlayer release]; // Decrease retain count 
    self.tempPlayer = [[LineUpsPlayer alloc] init]; // retain count increase by 1 or 2
    tempPlayer.playerCode = [tildeSeperator objectAtIndex:0];

    [matchLineUp.homeTeamPlayingEleven addObject:tempPlayer]; // retain count increase
}

So as you can see you retain your object more times then you release it so it eventually leaks. Probably your code may be rewritten this way:

for(int i = 0 ; i < [homeLineupArray count] ; i++) {   
        NSArray * tildeSeperator = [[homeLineupArray objectAtIndex:i] componentsSeparatedByString:@"~"];

       LineUpsPlayer* tempPlayer = [[LineUpsPlayer alloc] init]; // object's retain count is 1
        tempPlayer.playerCode = [tildeSeperator objectAtIndex:0];

        [matchLineUp.homeTeamPlayingEleven addObject:tempPlayer]; // container takes ownership of the object
        [tempPlayer release]; // we do not need to own this object as it is in container now
    }

Answer 2

First, you could change the release to an autorelease and move it to the line after the self is assigned.

Second, the addobject is adding it to a collection which retains it, and I don't see you removing it from that collection, so that's your 'leak'. However, I'm not sure there even is a leak, if you intended to leave it in the collection.

Answer 3

Rather than using the property, tempPlayer, use a local variable, and release after adding to the array:

for(int i = 0 ; i < [homeLineupArray count] ; i++) {   
    NSArray * tildeSeperator = [[homeLineupArray objectAtIndex:i] componentsSeparatedByString:@"~"];

    LineUpsPlayer* tempPlayer = [[LineUpsPlayer alloc] init];
    tempPlayer.playerCode = [tildeSeperator objectAtIndex:0];

    [matchLineUp.homeTeamPlayingEleven addObject:tempPlayer ];
    [tempPlayer release];
}

The array retains the objects you add - that's why you need to release the temporary object too.

Answer 4

I would simply do this.

for(int i = 0 ; i < [homeLineupArray count] ; i++) {   
    NSArray *tildeSeperator = [[homeLineupArray objectAtIndex:i] componentsSeparatedByString:@"~"];

    LineUpsPLayer *player = [[[LineUpsPlayer alloc] init] autorelease];
    player.playerCode = [tildeSeperator objectAtIndex:0];
    [matchLineUp.homeTeamPlayingEleven addObject:player];
}

You can also replace your loop with this:

for (NSString *lineup in homeLineupArray) {
    NSArray *tildeSeparator = [lineup componentsSeparatedByString:@"~"];
    ...
}

You don't usually want to save each item while iterating through an array to an instance variable since it keeps changing and you only reference it in the method.

Answer 5

As said above, I normally use a local variable to populate the mutable array. In other cases Instruments didnt show me any leak. So is this the right way to go about ?

for(int i =0 ; i <  ([arrayOfHomePlayers count]); i++ ) //creating home players detials object
{

    localString = [NSMutableString string];
    localString = [arrayOfHomePlayers objectAtIndex:i] ;
    NSArray * localPlayersArray = [localString componentsSeparatedByString:@"~"] ;
    localPlayerPosition = [ [PlayerPosition  alloc] init] ;

    NSArray * playerNameArray = [[localPlayersArray objectAtIndex:0] componentsSeparatedByString:@" "] ;
    localPlayerPosition.globalID   = [localPlayersArray objectAtIndex:1];

    [(teamFormationDetails.homePlayerList) addObject:localPlayerPosition] ;
    [localPlayerPosition release] ;