与NSArray互转，下面方法只需将NSDictionary替换成NSArray

1.JSON to NSDictionary

- (NSDictionary *)dictionaryWithJson:(NSString *)jsonString {
    if (jsonString == nil) {
        return nil;
    }
    
    NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
    NSError *err;
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&err];
    if(err) {
        NSLog(@"json解析失败：%@",err);
        return nil;
    }
    return dic;
}

2.NSDictionary to JSON

- (NSString*)jsonWithDictionary:(NSDictionary *)dic
{
    NSString *jsonString = nil;
    if ([NSJSONSerialization isValidJSONObject:dic])
    {
        NSError *error;
        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:&error];
        jsonString =[[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
        if (error) {
            NSLog(@"Error:%@" , error);
        }
    }
    return jsonString;
}