循环遍历反序列化类时的"Object reference not set to an instance of an object"

Question

EDIT：事实证明，我可以很好地反序列化，问题实际上是当我试图循环来获取问题时。尽管"对象引用未设置为对象的实例"，但仍出现相同错误。我之所以编辑这篇文章，是因为我无法删除帖子，因为它已经有答案了。

            //deserialize json
            ResponsesList responses = JsonConvert.DeserializeObject<ResponsesList>(_ResponseContent);
            if (responses != null)
            {
                //loop through responses
                foreach (ResponsesList.Data data in responses.data)
                    foreach (ResponsesList.Questions question in data.questions)
                        foreach (ResponsesList.Answer answer in question.answers)
                        {
                            //upsert each response
                            UpsertResponse(survey_id, data.respondent_id, question.question_id, answer.row, answer.col);
                        }
            }

这一行是发生错误的地方

foreach (ResponsesList.Questions question in data.questions)

这是我正在反序列化为的类

    //get_responses
    public class ResponsesList
    {
        public int status { get; set; }
        public List<Data> data { get; set; }
        public class Data
        {
            public string respondent_id { get; set; }
            public List<Questions> questions { get; set; }
        }
        public class Questions
        {
            public List<Answer> answers { get; set; }
            public string question_id { get; set; }
        }
        public class Answer
        {
            public string row { get; set; }
            public string col { get; set; }
        }
    }

Answer 1

我刚刚在LINQPad:中成功地反序列化了您的示例字符串

var str = 
@"{
    ""status"": 0,
    ""data"": [
        null,
        null
    ]
}";
JsonConvert.DeserializeObject<ResponsesList>(str).Dump();

这告诉我你的_ResponseContent不是你想象的那样。

Answer 2

想明白了。它只需要进行一些检查，以确保我试图循环通过的对象不是空的。

示例：

            //deserialize json
            ResponsesList responses = JsonConvert.DeserializeObject<ResponsesList>(_ResponseContent);
            if (responses != null)
            {
                //loop through responses
                foreach (ResponsesList.Data data in responses.data)
                    if (data != null)
                    {
                        foreach (ResponsesList.Questions question in data.questions)
                            if (question != null)
                            {
                                foreach (ResponsesList.Answer answer in question.answers)
                                {
                                    //upsert each response
                                    UpsertResponse(survey_id, data.respondent_id, question.question_id, answer.row, answer.col);
                                }
                            }
                    }
            }

不过，我感谢大家的回复。

Answer 3

当我遇到这个错误时，我通过在执行循环之前添加一个null测试来修复我的错误。

Answer 4

我会使用这个网站来创建您的类：http://json2csharp.com/

这就是它吐出的：

public class RootObject
{
    public int status { get; set; }
    public List<object> data { get; set; }
}