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Can Json.NET populate readonly fields in a class?

开发者 https://www.devze.com 2023-01-25 05:37 出处:网络
I haven\'t seen much information about Json.NET supporting deserializing objects with readonly fields. I do notice that the .NET DataContract and DataMember attri开发者_JS百科butes allow for populatin

I haven't seen much information about Json.NET supporting deserializing objects with readonly fields. I do notice that the .NET DataContract and DataMember attri开发者_JS百科butes allow for populating readonly fields during deserializtion, but Json.NET doesn't seem to support this, at least from the behavior I'm seeing.


Not the most elegant solution, but you can extend the DefaultConstractResolver to do it:

public class ContractResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);
        property.Writable = CanSetMemberValue(member, true);
        return property;
    }

    public static bool CanSetMemberValue(MemberInfo member, bool nonPublic)
    {
        switch (member.MemberType)
        {
            case MemberTypes.Field:
                var fieldInfo = (FieldInfo)member;

                return nonPublic || fieldInfo.IsPublic;
            case MemberTypes.Property:
                var propertyInfo = (PropertyInfo)member;

                if (!propertyInfo.CanWrite)
                    return false;
                if (nonPublic)
                    return true;
                return (propertyInfo.GetSetMethod(nonPublic) != null);
            default:
                return false;
        }
    }
}

I have just remove one little check from the CanSetMemberValue method. Unfortunately it's neither virtual nor an instance method, so I had to override CreateProperty as well.


This can be done now. Declare your properties using the JsonProperty attribute, and ensure that they have a protected set declared:

[JsonProperty("Name")] public string Name {get; protected set;}

This didn't work for me when using only a get, but works perfectly with the protected set.


afai can see changing a field to readonly results in a null value after deserialization. I had a working sample for another question (modified as shown below), and that's the behaviour I see.

public class NameAndId
{
    public string name;
    public int id; 
}

public class Data
{
    public NameAndId[] data;
}

public class Target
{
    public string id;
    public readonly NameAndId from;
    public DateTime updated_time;
    public readonly string message;
    public Data likes;
}

public class Program
{
    static void Main(string[] args)
    {
        string json = File.ReadAllText(@"c:\temp\json.txt");
        Target newTarget = JsonConvert.DeserializeObject<Target>(json);
    }
}
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