- (NSDictionary *)dictionaryWithJsonString:(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;
}

字典转字符串

-(NSString *)convertToJsonData:(NSDictionary *)dict{
    NSError *error;
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dict options:NSJSONWritingPrettyPrinted error:&error];
    NSString *jsonString;
    if (!jsonData) {
        NSLog(@"%@",error);
    }else{
        jsonString = [[NSString alloc]initWithData:jsonData encoding:NSUTF8StringEncoding];

    }

    NSMutableString *mutStr = [NSMutableString stringWithString:jsonString];
    NSRange range = {0,jsonString.length};

    //去掉字符串中的空格
    [mutStr replaceOccurrencesOfString:@" " withString:@"" options:NSLiteralSearch range:range];
     NSRange range2 = {0,mutStr.length};

     //去掉字符串中的换行符

    [mutStr replaceOccurrencesOfString:@"\n" withString:@"" options:NSLiteralSearch range:range2];
    return mutStr;
}