1.NSArray转换成JSONString

 //NSArray+JSONString.h
@interface NSArray (JSONString)
- (NSString *)jsonStringWithPRettyPrint:(BOOL)prettyPrint;
@end

@implementation NSArray (JSONString)
-(NSString*) jsonStringWithPrettyPrint:(BOOL) prettyPrint {
    NSError *error;
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:self
                                                       options:(NSJSONWritingOptions) (prettyPrint ? NSJSONWritingPrettyPrinted : 0)
                                                         error:&error];

    if (! jsonData) {
        NSLog(@"jsonStringWithPrettyPrint: error: %@", error.localizedDescription);
        return @"[]";
    } else {
        return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
    }
}
@end

2.NSDictionary 转成 JSONString

 //NSDictionary+JSONString.h
@interface NSDictionary (JSONString)
-(NSString*) jsonStringWithPrettyPrint:(BOOL) prettyPrint;
@end

//NSDictionary+JSONString.m
@implementation NSDictionary (JSONString)

  -(NSString*) jsonStringWithPrettyPrint:(BOOL) prettyPrint {
     NSError *error;
     NSData *jsonData = [NSJSONSerialization dataWithJSONObject:self
                                                   options:(NSJSONWritingOptions)    (prettyPrint ? NSJSONWritingPrettyPrinted : 0)
                                                     error:&error];

     if (! jsonData) {
        NSLog(@"jsonStringWithPrettyPrint: error: %@", error.localizedDescription);
        return @"{}";
     } else {
        return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
     } 
 }
@end