c# - 带有 ISerializable 的 BinaryFormatter OptionalField

Question

我创建了一个测试可序列化对象：

[Serializable]
public class TestObject : ISerializable
{
    public string FirstName;
    public TestObject()
    {
    }

    public TestObject(SerializationInfo info, StreamingContext context)
    {
        FirstName = info.GetString("firstName");
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("firstName", FirstName);
    }
}

然后序列化它：

var test = new TestObject { FirstName = "John" };
using (var stream = new FileStream(@"c:\temp\test.dat", FileMode.Create, FileAccess.Write))
{
    var formatter = new BinaryFormatter();
    formatter.Serialize(stream, test);
}

我更改了类，使其具有 OptionalFied 并尝试反序列化旧的序列化对象：

[Serializable]
public class TestObject : ISerializable
{
    public string FirstName;

    [OptionalField]
    public string SecondName;

    public TestObject()
    {
    }

    public TestObject(SerializationInfo info, StreamingContext context)
    {
        FirstName = info.GetString("firstName");
        SecondName = info.GetString("secondName");
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("firstName", FirstName);
    }

当我更改构造函数以读取新的可选字段时，在“SecondName = info.GetString("secondName");”处抛出异常：

   using (var stream = new FileStream(@"c:\temp\test1.dat", FileMode.Open, FileAccess.Read))
{
    var formatter = new BinaryFormatter();
    var myInstance = (TestObject)formatter.Deserialize(stream);
}

当您实现 ISerializable 时，是否真的不支持 OptionalFieldAttribute？

Answer 1

对于旧的序列化对象，不会有 secondname 字段，因此它的 SerializationEntry 将不存在。

在访问值之前，您需要检查是否存在条目：

    foreach (SerializationEntry entry in info) 
    { 
        switch (entry.Name) 
        { 
            case "firstname": 
                Firstname = (string)entry.Value; 
            break; 
            case "secondname": 
                Secondname = (string)entry.Value;
            break; 
        }
    }