NSMutableArray replace object

Question

I try to find object in my array and if success I need to replace object from my array to new object

 for (id existingSig in allSignature)
   if ([[existingSig objectForKey:@"SignatureName"] isEqualToString:[item objectForKey:@"name"]])
    {    
      [allSignature removeObject:existingSig];
      [allSignature addObject:[NSDictionary dictionaryWithObjectsAndKeys:@"1", @"SignatureIsRich", [item objectForKey:@"name"], @"SignatureName", generatedID, @"SignatureUniqueId", nil]];
     }

I have error 'NSCFArray: 0x100551f10> was mutated while being enumerated'

acorc · Accepted Answer · 2012-05-05 00:37:25Z

As others have said, you cannot mutate a MutableArray while it is being Enumerated. You could handle it by having two arrays of what to remove and what to add after the loop.

NSMutableArray *remove = [NSMutableArray array];
NSMutableArray *add = [NSMutableArray array];
for (id existingSig in allSignature){
   if ([[existingSig objectForKey:@"SignatureName"] isEqualToString:[item objectForKey:@"name"]])
    {    
      // Add to the array of objects to be removed
      [remove addObject:existingSig];
      // Add to the array of objects to be added
      [add addObject:[NSDictionary dictionaryWithObjectsAndKeys:@"1", @"SignatureIsRich", [item objectForKey:@"name"], @"SignatureName", generatedID, @"SignatureUniqueId", nil]];
     }
}
[allSignature removeObjectsInArray:remove]; // Remove objects
[allSignature addObjectsFromArray:add]; // Add new objects

Yusuf X · Accepted Answer · 2012-05-04 23:55:47Z

2

The easiest way is to make a copy and iterate over that, then modify the original.

answered May 4, 2012 at 23:55

Yusuf X

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1 Comment

hypercrypt Over a year ago

e.g.: for (id existingSig in [allSignature copy])... / for (id existingSig in [[allSignature copy] autorelease])... depending on if you're using ARC.

Colin Wheeler · Accepted Answer · 2012-05-05 01:26:37Z

I have a map array method I have in a NSArray Category for this very purpose

- (NSArray *) cw_mapArray:(id (^)(id obj))block
{
    NSMutableArray * cwArray = [[NSMutableArray alloc] init];
    [self cw_each:^(id obj, NSUInteger index, BOOL *stop) {
        id rObj = block(obj);
        if (rObj) {
            [cwArray addObject:rObj];
        }
    }];
    return cwArray;
}

this way I can get a new array and then just change the array with the new array. You can change cw_each to enumerateObjectsUsingBlock:. Basically this is simple, if you want to map the object to the new array you just return the object as is in the block, otherwise modify it and return that or if you don't want to map the object to the new array then return nil. Its not very much code and works wonderfully.

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