Why I could not serialize a tuple in C#? [duplicate]

Question

Possible Duplicate:
Why XML-Serializable class need a parameterless constructor

I'm trying to serialize a tuple in my code:

List<List<Tuple<String, CodeExtractor.StatementNode>>> results = null; results = extractor.ExtractSourceCode(sourceCode); FileStream fs = new FileStream(@"C:\Projects\Test\ast.xml", FileMode.Create);  XmlSerializer formatter = new XmlSerializer(     typeof(List<List<Tuple<String, CodeExtractor.StatementNode>>>));  formatter.Serialize(fs, results);  fs.Close(); 

but it was failed and catch the exception like this:

System.Tuple`2[System.String,CodeExtractor.StatementNode] cannot be serialized because it does not have a parameterless constructor.

and I'm do sure the CodeExtractor.StatementNode could be serialized.

Answer 1

For XmlSerializer to be able to do its job it needs a default contructor. That is a constructor that takes no arguments. All the Tuple<...> classes have a single constructor and that constructor takes a number of arguments. One for each value in the tuple. So in your case the sole constructor is

Tuple(T1 value1, T2 value2) 

The serializer is looking for a constructor with no arguments and because it can't find it, you get the exception.

you could create a mutable class, that could be substituted for tuples for the purpose of serialization

class MyTuple<T1, T2> {     MyTuple() { }      public T1 Item1 { get; set; }     public T2 Item2 { get; set; }      public static implicit operator MyTuple<T1, T2>(Tuple<T1, T2> t)     {          return new MyTuple<T1, T2>(){                       Item1 = t.Item1,                       Item2 = t.Item2                     };     }      public static implicit operator Tuple<T1, T2>(MyTuple<T1, T2> t)     {         return Tuple.Create(t.Item1, t.Item2);     } } 

You could then use it the following way

XmlSerializer formatter = new XmlSerializer(     typeof(List<List<MyTuple<String, CodeExtractor.StatementNode>>>));  formatter.Serialize(fs, results.SelectMany(                               lst => lst.Select(                                         t => (MyTuple)t                                      ).ToList()                               ).ToList());