Method always re-writing json file - objective-c

Question

NSURL *url = [NSURL URLWithString:#"file://localhost/Users/admin/Desktop/JSON/vivijson.json"];
NSDictionary *regDict = [[NSDictionary alloc] initWithObjectsAndKeys:self.loginString, #"login",
self.nameString, #"name",
self.lastNameString, #"lastName",
self.emailString, #"email",
self.numberString, #"number", nil];
NSError *error;
NSMutableArray *regMutArray = [[NSMutableArray alloc] init];
[regMutArray addObject:regDict];
NSData *jsonConvRegArrayData = [NSJSONSerialization dataWithJSONObject:regMutArray options:NSJSONWritingPrettyPrinted error:&error];
NSString *jsonRegString = [[NSString alloc] initWithData:jsonConvRegArrayData encoding:NSUTF8StringEncoding];
[jsonConvRegArrayData writeToURL:url atomically:YES];
This method are re-writing JSON, and start it again, but i need to add some to my JSON.

Answer 1

You should first read the exiting JSON into a mutable array using JSONObjectWithData using NSJSONReadingMutableContainers as the reading options. Then add the new array element to the mutable array returned by JSONObjectWithData and then convert it back to an JSON using dataWithJSONObject
Here's the code.
NSURL *url = [NSURL URLWithString:#"file://localhost/Users/Shared/vivijson.json"];
NSDictionary *regDict = [[NSDictionary alloc] initWithObjectsAndKeys:#"self.loginString, #"login",
self.nameString, #"name",
self.lastNameString, #"lastName",
self.emailString, #"email",
self.numberString, #"number", nil];
NSError *error;
NSMutableArray *regMutArray = [[NSMutableArray alloc] init];
[regMutArray addObject:regDict];
NSData *data = [NSData dataWithContentsOfURL:url];
NSMutableArray *array = nil;
if (data)
array = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
if (array == nil)
{
array = [[NSMutableArray alloc] init];
}
[array addObjectsFromArray:regMutArray];
NSData *jsonConvRegArrayData = [NSJSONSerialization dataWithJSONObject:array options:NSJSONWritingPrettyPrinted error:&error];
NSString *jsonRegString = [[NSString alloc] initWithData:jsonConvRegArrayData encoding:NSUTF8StringEncoding];
[jsonRegString writeToURL:url atomically:true encoding:NSUTF8StringEncoding error:nil];