Question

I have a simple code:

NSMutableArray *arrayCheckList = [[NSMutableArray alloc] init];
[arrayCheckList addObject:[NSMutableDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"2011-03-14 10:25:59 +0000",@"Exercise at least 30mins/day",@"1",nil] forKeys:[NSArray arrayWithObjects:@"date",@"checkListData",@"status",nil]] ];
[arrayCheckList addObject:[NSMutableDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"2011-03-14 10:25:59 +0000",@"Take regular insulin shots",@"1",nil] forKeys:[NSArray arrayWithObjects:@"date",@"checkListData",@"status",nil]]];

Now I want to add a specific index of above array to a dictionary. Below are two way, which one is better and why? What are the specific drawbacks of the latter?

NSDictionary *tempDict = [[NSDictionary alloc] initWithDictionary:[arrayCheckList objectAtIndex:1]];

OR

NSDictionary *tempDict = [arrayCheckList objectAtIndex:1];

What would the impact on the latter since I am not doing any alloc/init in it?

Answer 1

1:

NSDictionary *tempDict = [[NSDictionary alloc] initWithDictionary:[arrayCheckList objectAtIndex:1]];

Creates a new immutable dictionary object as a copy of the original one. If you add objects to the mutable dictionary in your arrayCheckList they will not be added to your copied reference.

2:

NSDictionary *tempDict = [arrayCheckList objectAtIndex:1];

This directly pulls the mutable dictionary from your array and not a copy. The following two lines will be equivalent:

[[arrayCheckList objectAtIndex:1] addObject:something];
[tempDict addObject:something];