Getting error when added NSNumber to an array

Question

When my program gets to the line: [userNumSequence addObject:[NSNumber numberWithInteger: sequenceNumber]]; it gets the error: Program received signal: “EXC_BAD_ACCESS”.

All I'm wanting to do is to store an integer in the array.

//  JBNumberGeneration.m

#import "JBNumberGeneration.h"


@implementation JBNumberGeneration

- (id) init{ 
    if (self = [super init]){ 
        userNumSequence = [NSMutableArray arrayWithCapacity:0]; 
    } return self; 
}

-(IBAction)logSequenceNumber:(id)sender{
    NSString *titleOfButton = [sender title];
    int sequenceNumber = [titleOfButton integerValue];
    i=0;

    [userNumSequence addObject:[NSNumber numberWithInteger: sequenceNumber]];

    //int currentNum = [((NSNumber*)[userNumSequence objectAtIndex: i]) integerValue];
    //NSLog(@"%i", currentNum);

    int count = [userNumSequence count];
    NSLog(@"Array size: %i", count);

    i++;
}
@end

//  JBNumberGeneration.h

#import <Cocoa/Cocoa.h>


@interface JBNumberGeneration : NSObject {
    IBOutlet NSTextField *displayLabel;
    int randNum;
    int level;
    int i;
    NSMutableArray* userNumSequence;
}

-(IBAction)logSequenceNumber:(id)sender;
@end

Answer 1

EXC_BAD_ACCESS usually occurs when you try to access a member that has already been deallocated. Because you are calling [NSMutableArray arrayWithCapacity:] in your init function, it may have already been released by the time logSequenceNumber:(id)sender is called. Try adding @property (nonatomic, retain) NSMutableArray* userNumSequence to your @interface and @synthesize userNumSequence to your @implementation. Then call self.userNumSequence = [NSMutableArray arrayWithCapacity:0] in your init method. Don't forget to set it to nil in dealloc.

EDIT: Also, just to be clear the Cocoa memory management naming standards are like this:

1. If you call [[Object alloc] initSomehow], or [object retain] you are responsible for releasing it (calling init methods will automatically call retain).
2. If you call methods like [Object objectWithSomething:something], these are usually autoreleased and will be released sometime in the future. You should never assume these exist beyond the scope in with they are created. According to the Cocoa documentation, scope includes the call stack. If a: calls b: which calls c:, and c: returns an autoreleased object, it can be passed safely all the way back up for a: to use. Beyond that it is released. This is at least my interpretation of the explanation of autorelease.

If you need to use something for the lifetime of your object, retain it when you get it and release it in dealloc.