collections reference in obj-c - objective-c

Question

I'm new to Obj-C, and I have a little problem here.
I'm trying insert the values from a temp Dictionary into an array
NSMutableDictionary *myDict = [[NSMutableDictionary alloc] init];
NSMutableArray *myArray = [[NSMutableArray alloc] init];
[myDict setObject:[NSNumber numberWithInt:100] forKey:#"Record"];
[myDict setObject:#"www" forKey:#"Name"];
[myArray addObject:myDict];
[myDict setObject:[NSNumber numberWithInt:80] forKey:#"Record"];
[myDict setObject:#"eee" forKey:#"Name"];
[myArray addObject:myDict];
[myDict setObject:[NSNumber numberWithInt:70] forKey:#"Record"];
[myDict setObject:#"rrr" forKey:#"Name"];
[myArray addObject:myDict];
[myDict setObject:[NSNumber numberWithInt:0] forKey:#"Record"];
[myDict setObject:#"ttt" forKey:#"Name"];
[myArray addObject:myDict];
NSLog(#"myArray %#",myArray);
Regardless of the bad implementation code here (and my bad English as well :p), what I'm trying to figure out is how do I clean myDict after each insertion in myArray.
Using [myDict removeAllObjects]; after each addObject is giving me an empty array at the end.
Thanks!
Thanks for all your answers, with [myArray addObject:[[myDict copy] autorelease]]; the code works just fine.

Answer 1

The problem here is you're adding the exact same mutable dictionary to the array over and over. So your array is simply a collection of references to the exact same object. Therefore it shouldn't be surprising that every object in your array is identical to the last one.
In order to do what you want, you have two options. The first is to copy your mutable dictionary each time and add that copy to the array. You can do this by using
[myArray addObject:[[myDict copy] autorelease]];
The other solution is to use separate dictionaries to begin with. Instead of mutating a mutable dictionary each time, you could construct a brand new NSDictionary:
[myArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:100], #"Record",
#"www", #"Name",
nil]];
[myArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:80], #"Record",
#"eee", #"Name",
nil]];

Answer 2

I think you need to copy the dictionary before you add it to the array...
[myArray addObject:[[myDict copy] autorelease]];
Then you can use [myDict removeAllObjects] as normal.

Answer 3

NSMutableDictionary * as * suggests is a pointer to the object of dictionary.
So when you add it to an array it is still the same object - pointed by myDict as well as by the element in the array.
Therefore, I suggest you create new dictionary after each add:
NSMutableDictionary *myDict = [[NSMutableDictionary alloc] init];
NSMutableArray *myArray = [[NSMutableArray alloc] init];
[myDict setObject:[NSNumber numberWithInt:100] forKey:#"Record"];
[myDict setObject:#"www" forKey:#"Name"];
[myArray addObject:myDict];
myDict = [[NSMutableDictionary alloc] init];
[myDict setObject:[NSNumber numberWithInt:80] forKey:#"Record"];
[myDict setObject:#"eee" forKey:#"Name"];
[myArray addObject:myDict];
I assume you are using ARC in the code above.
Although, the more Objective-C'ish way would be to do:
[myArray addObject: [NSDictionary dictionaryForObjectsAndKeys: [NSNumber numberWithInt:80], #"Record", #"www", #"Name"]];