How to replace an object in an NSMutableArray at a given index with a new object

Question

I have an NSMutableArray object (retained, synthesized as all) that is initiated just fine and I can easily add objects to it using the addObject: method. But if I want to replace an object at a certain index with a new one in that NSMutableArray, it doesn't work.

For example:

ClassA.h:

@interface ClassA : NSObject {
    NSMutableArray *list;
}

@property (nonatomic, copy, readwrite) NSMutableArray *list;

@end

ClassA.m:

#import "ClassA.h"

@implementation ClassA

@synthesize list;

- (id)init 
{
    [super init];
    NSMutableArray *localList = [[NSMutableArray alloc] init];
    self.list = localList;
    [localList release];
    //Add initial data
    [list addObject:@"Hello "];
    [list addObject:@"World"];
}


// Custom set accessor to ensure the new list is mutable
- (void)setList:(NSMutableArray *)newList 
{
    if (list != newList) 
    {
        [list release];
        list = [newList mutableCopy];
    }
}

-(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex
{
    int i = [theIndex intValue]-1;
    [self.list replaceObjectAtIndex:i withObject:newTitle];
    NSLog((NSString *)[self.list objectAtIndex:i]);  // gives the correct output
}

However, the change remains true only inside the method. from any other method, the

NSLog((NSString *)[self.list objectAtIndex:i]);

gives the same old value.

How can I actually get the old object replaced with the new one at a specific index so that the change can be noticed from within any other method as well.

I even modified the method like this, but the result is the same:

-(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex
{
    int i = [theIndex intValue]-1;

    NSMutableArray *localList = [[NSMutableArray alloc] init];
    localList = [localList mutableCopy];
    for(int j = 0; j < [list count]; j++)
    {
        if(j == i)
        {
            [localList addObject:newTitle];
            NSLog(@"j == 1");
            NSLog([NSString stringWithFormat:@"%d", j]);
        }
        else
        {
            [localList addObject:(NSString *)[self.list objectAtIndex:j]];
        }
    }
    [self.list release];
    //self.list = [localList mutableCopy];
    [self setList:localList];
    [localList release];
}

Please help out guys :)

Answer 1

This does the trick:

[myMutableArray replaceObjectAtIndex:index withObject:newObject];