Generic Dictionary Wrapper Class Cannot be Restored from ViewState

The .NET 2.0 generic Dictionary class can be serialised to and deserialised from the ViewState of a web application but extending the Dictionary class to derive a named collection grounded in the business domain requires some extra attention. Essentially, the derived class needs to call a specific constructor in the base class when deserialisation occurs and this doesn't happen implicitly (List-based classes seem to work fine without modification). Note: the derived class will serialise happily--deserialisation is the problem).

The System.Collections.Generic.Dictionary class defines a constructor used to restore the Dictionary's internal data during the deserialisation process:

"Initializes a new instance of the Dictionary class with serialized data."

protected Dictionary (
SerializationInfo info,
StreamingContext context
)

Constructors are not inherited in C# so a wrapper class must explicitly define this constructor and pass the data back up the inheritance hierarchy to the base Dictionary class:

[Serializable]
public class CustomCollection : Dictionary
{
protected CustomCollection (
System.Runtime.Serialization.SerializationInfo info,
System.Runtime.Serialization.StreamingContext context
) : base (info, context)
{
// no implementation
}
}

Depending on how you construct your wrapper class, you'll most likely want to define additional constructors as well or the default (empty) constructor at a minimum as it will no longer be injected by the compiler with the deserialisation constructor present.

Without this constructor, I was receiving a corrupted ViewState exception

The state information is invalid for this page and might be corrupted.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.