Ryan's Tech Blog

Problem: .NET framework classes don’t use interfaces enough

Specific example: DataSource / DataBind()are separately defined on Repeater and GridView, (and Control, and many, many others), and my abstract base class doesn’t care which option an implementor chooses, it just wants to bind the data however the base control wants it.

Possible Solutions:

• Define interface IDataBinding, class MyRepeater : Repeater, IDataBinding, class MyGridView : GridView, IDataBinding, etc.
• Define interface IDataBinding, upgrade to C# 3, use extension methods to add IDataBinding nope, extension methods can’t do this
• Copy/paste identical code from my base class into concrete classes
• Use reflection to set DataSource and call DataBind(), completely sidestepping the C# type system

Problem: .NET framework classes not designed for extension: “cannot override inherited member 'System.Collections.Generic.Dictionary<X, Y>.Add(X, Y)' because it is not marked virtual, abstract, or override”

Specific Example: Extending System.Collections.Generic.Dictionary to do some permit a list of values for one key, so adding the first item is stored as a single value, but adding a second value to the same key stores both values in a list. Error message is: “cannot override inherited member 'System.Collections.Generic.Dictionary<X, Y>.Add(X, Y)' because it is not marked virtual, abstract, or override”

Possible Solutions:

• Define wrapper classes that encapsulates the framework class and implements all the base interfaces, with the vast majority of the code being straight delegation to the framework class:

  class MyDict : IDictionary, [other interfaces...] {
  private Dictionary<X,Y> dict = new Dictionary<X,Y>;
  public bool Contains(X key){ return dict.Contains(key);}
  [... other simple wrappers...]
  }

• Find a less appropriate framework class that is designed for extension, duplicate behavior of the proper framework class manually, eg: add run-time type checks for Hashtable.Add(object, object) in place of the letting the compiler handle the types as in Dictionary<X,Y>.Add(X, Y)
• Extend Dictionary<X,Y>, define a method AddList(X,Y), and avoid using IDictionary in the rest of my code
• Upgrade the C# 3, use extension to add function AddList to IDictionary, be sure to include those extensions on every consumer of IDictionary

Problem: .NET framwork classes not designed for extension: members declared private/ internal / protected internal

Specific Example: Storing additional data in ViewState on 2 different controls that have different base classes. One is a user control, another extends RadioButtonList to provide different UI for the same data

Possible solutions:

• Upgrade to C# 3, use extension methods to add functions nope, extension methods can only see public members, ViewState is protected
• Use reflection to set ViewState
• Copy/paste code into each control
• Define interface IPublicViewstate, class MyRadioButtonList : RadioButtonList, IPublicViewState, class MyUserControl : UserControl, IPublicViewState, etc

As Nathan said, I’m stuck between a rock and IHardPlace.