c# - BinaryFormatter OptionalField with ISerializable -

i create test serializable object:

[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);     } } 

and serialize it:

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); } 

i change class has optionalfied , try deserialize old serialized object:

[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);     } 

when change constructor read new optional field, exception thrown @ "secondname = info.getstring("secondname");":

   using (var stream = new filestream(@"c:\temp\test1.dat", filemode.open, fileaccess.read)) {     var formatter = new binaryformatter();     var myinstance = (testobject)formatter.deserialize(stream); } 

is case optionalfieldattribute not supported when implement iserializable?

for old serialzed object there not secondname field, serializationentry wouldn't exist.

you need check if entry exists before access value:

    foreach (serializationentry entry in info)      {          switch (entry.name)          {              case "firstname":                  firstname = (string)entry.value;              break;              case "secondname":                  secondname = (string)entry.value;             break;          }     }