c# - Deserializing .NET Dictionary using ISerializable -

i have problems getting de-/serialization of dictionary working when implementing iserializable in enclosing class. seems able automatically de-/serialize if apply serializableattribute. need check deserialized dictionary in process however, need iserializable working.

i set little test sure wasn't due other problems. test class looks this:

[serializable] class test : iserializable {     private dictionary<string, int> _dict;      public test()     {         var r = new random();         _dict = new dictionary<string, int>()         {             { "one", r.next(10) },             { "two", r.next(10) },             { "thr", r.next(10) },             { "fou", r.next(10) },             { "fiv", r.next(10) }         };     }      protected test(serializationinfo info, streamingcontext context)     {         // here _dict.count == 0         // found dictionary no content?         _dict = (dictionary<string, int>)info.getvalue("foo", typeof(dictionary<string, int>));     }      public void getobjectdata(serializationinfo info, streamingcontext context)     {         info.addvalue("foo", _dict, typeof(dictionary<string, int>));     }      public override string tostring()     {         var sb = new stringbuilder();         foreach (var pair in _dict)             sb.append(pair.key).append(" : ").append(pair.value).appendline();         return sb.tostring();     } } 

and main test it:

static void main(string[] args) {     var t1 = new test();     console.writeline(t1);     var formatter = new binaryformatter();     using (var stream = new filestream("test.test", filemode.create, fileaccess.write, fileshare.none))         formatter.serialize(stream, t1);      test t2;     using (var stream = new filestream("test.test", filemode.open, fileaccess.read, fileshare.read))         t2 = (test)formatter.deserialize(stream);     console.writeline(t2);     console.readline(); } 

the output in console same before , after. commented in test class, overloaded constructor doesn't read content in deserialized dictionary.

am doing wrong or bug/subtle side effect?

dictionary<tkey, tvalue> implements ideserializationcallback , defers completion of de-serialization until whole graph of objects read back. can see how implemented on reference source :

protected dictionary(serializationinfo info, streamingcontext context)              {     //we can't keys , values until entire graph has been deserialized     //and have resonable estimate gethashcode not going fail.  time being,     //we'll cache this.  graph not valid until ondeserialization has been called.     hashhelpers.serializationinfotable.add(this, info); } 

to force completion call _dict.ondeserialization() in code:

protected test(serializationinfo info, streamingcontext context) {     // here _dict.count == 0     // found dictionary no content?     _dict = (dictionary<string, int>)info.getvalue("foo", typeof(dictionary<string, int>));      _dict.ondeserialization(null);      // content restored.     console.writeline("_dict.count={0}", _dict.count); } 

ps: hashset<t>, sortedset<t>, linkedlist<t> , maybe few other container types exhibit same behavior