Styjun

I need to add NSDictionary into NSMutableArray.

First I have created a NSMutableDictionary with a key value from other structure like this:

for (NSString *key in selectedFiltersByUser) 
 [filters_data setObject:key forKey:@"key"];
 [filters_data setObject:selectedFiltersByUser[key] forKey:@"value"];

 // Added filter selected id's into Array for all query_params
 [query_params addObject:filters_data];

selectedFiltersByUser is a Dictionary like this:

category_id = "XXX";
sort = "last_updated_asc";
status = "rejected_by_seller";

and for each key:value in this Dictionary I create a new NSMutableDictionary like this:

 key: category_id,
 value: XXX

And this new NSMutableDictionary added into NSMutableArray like this:

 for (NSString *key in selectedFiltersByUser) 
 [filters_data setObject:key forKey:@"key"];
 [filters_data setObject:selectedFiltersByUser[key] forKey:@"value"];

 // Added filter selected id's into Array for all query_params
 [query_params addObject:filters_data];

But when adding this NSMutableDictionary into NSMutableArray it doesn't replace the last object and I get this in query_params:

 
 key: category_id,
 value: XXX
 ,
 
 key: category_id,
 value: XXX
 ,
 
 key: category_id,
 value: XXX
 

I need this:

 key: category_id,
 value: XXX
 ,
 
 key: sort,
 value: last_updated_asc
 ,
 
 key: status,
 value: rejected_by_seller
 

I don't know how to replace the last object added.

try to [NSMutableDictionary alloc] init] in the for loop and then add data.

because when you init out of the loop, Every time it will go to inside loop and key is same so it will overwrite with new value. if you init into the loop it will create new one.

for (NSString *key in selectedFiltersByUser) 

 //INIT HERE YOUR DICTIONARY
 NSMutableDictionary *filters_data = [NSMutableDictionary alloc] init];

 [filters_data setObject:key forKey:@"key"];
 [filters_data setObject:selectedFiltersByUser[key] forKey:@"value"];

 // Added filter selected id's into Array for all query_params
 [query_params addObject:filters_data];

Adding a dictionary to the array does not copy the dictionary. It store a reference to the object (dictionary) to the array, so a reference to the identical dictionary is added every time.

Overwriting the contents of the dictionary changes the identical dictionary, which is stored multiple times in the array.

You have to create a new dictionary every time. There is no reason to create a mutable one.

As the comments have pointed out your issue is due to the reference semantics of Objective-C collections, i.e. they contain references to existing objects and not copies of them. So if you add the same NSMutableDictionary multiple times to an NSMutableArray as your code does you end up with every element of the array being a reference to the same dictionary. The simple fix already suggested is to allocate the dictionary inside your loop:

for (NSString *key in selectedFiltersByUser)

 NSMutableDictionary *filters_date = [NSMutableDictionary new];
 [filters_data setObject:key forKey:@"key"];
 [filters_data setObject:selectedFiltersByUser[key] forKey:@"value"];
 [query_params addObject:filters_data];

However you can make it simpler and avoid the problem altogether. You are already indexing selectedFiltersByUser, you can also index filters_data in a similar way giving you:

for (NSString *key in selectedFiltersByUser)

 NSMutableDictionary *filters_date = [NSMutableDictionary new];
 filters_data[@"key"] = key;
 filters_data[@"value"] = selectedFiltersByUser[key];
 [query_params addObject:filters_data];

but that still leaves you with the allocation, which you can remove by using a dictionary literal:

for (NSString *key in selectedFiltersByUser)

 NSDictionary *filters_date
 = @ @"key": key,
 @"value": selectedFiltersByUser[key]
 ;
 [query_params addObject:filters_data];

Now there the allocation is handled automatically by the compiler and you get an NSDictionary. The final option is to drop filters_date altogether:

for (NSString *key in selectedFiltersByUser)

 [query_params addObject:@ @"key": key,
 @"value": selectedFiltersByUser[key]
 
 ];

You may find that using dictionary (and array) literals helps you avoid allocation mistakes and creating mutable structures when they are not required. HTH