字典与Json字符串相互转换

    // 字典转换成Json字符串
    NSDictionary * testDict = @{@"hid":@"1",
                                @"cut_price":@"2",
                                @"cut_num":@"3",
                                @"goods_id":@"4",
                                @"pool_id":@"5"};
    NSError * error = nil;
    NSData * jsonData = [NSJSONSerialization dataWithJSONObject:testDict options:NSJSONWritingPrettyPrinted error:&error];
    NSString * jsonStr = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
    
    // 将json字符串转换成字典
    NSData * getJsonData = [jsonStr dataUsingEncoding:NSUTF8StringEncoding];
    NSDictionary * getDict = [NSJSONSerialization JSONObjectWithData:getJsonData options:NSJSONReadingMutableContainers error:&error];