反序列化，以使字段为空列表而不是null [英] Deserializing such that a field is an empty list rather than null

问题描述

如果我有这样的课程:

[DataContract(Name = "", Namespace = "")]
public class MyDataObject
{
    [DataMember(Name = "NeverNull")]
    public IList<int> MyInts { get; set; }
}

当以下字符串反序列化时，有没有办法使MyInts字段成为非空的空列表?

Is there a way I can make MyInts field a non-null empty list when the following string is deserialized?

string serialized = @"{""NeverNull"":null}";

MyDataObject myDataObject = JsonConvert.DeserializeObject<MyDataObject>(serialized);

我正在使用Newtonsoft.Json

I’m using Newtonsoft.Json

我问的原因是我要解析一个相当复杂的json请求，它包含对象列表的嵌套，并且我想通过反序列化代码来创建这些对象，以便避免很多空检查:

The reason I ask is that I have a fairly complicated json request to parse, it contains nests of lists of objects and I'd like the deserialization code to create these object so I can avoid lots of null checks:

if (foo.bar != null)
{
    foreach (var bar in foo.bar)
    {
        if (bar.baz != null)
        {
            foreach (var baz in bar.baz)
            {
                ...

推荐答案

也许添加反序列化后的回调，以便在反序列化结束时对此进行检查?

Perhaps add a post-serialization callback that checks this at the end of deserialization?

[DataContract(Name = "", Namespace = "")]
public class MyDataObject
{
    [OnDeserialized]
    public void OnDeserialized(StreamingContext context)
    {
        if (MyInts == null) MyInts = new List<int>();
    }
    [DataMember(Name = "NeverNull")]
    public IList<int> MyInts { get; set; }
}

还要注意，JsonConvert(与DataContractSerializer不同)执行默认的构造函数，因此通常您还可以添加一个默认的构造函数:

Note also that JsonConvert (unlike DataContractSerializer) executes the default constructor, so usually you could also have just added a default constructor:

    public MyDataObject()
    {
        MyInts = new List<int>();
    }

但是，在这种情况下，爆炸 "NeverNull":null在反序列化期间将其更改回null，因此为什么我在上面使用了回调.

however, in this case the explict "NeverNull":null changes it back to null during deserialization, hence why I've used a callback above instead.

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