ICustomTypeDescriptor, TypeDescriptionProvider, TypeConverter, and UITypeEditor

Question

I'm trying to get an overall understanding of how you use ICustomTypeDescriptor, TypeDescriptionProvider, TypeConverter, and UITypeEditor to change how a PropertyGrid displays and interfaces with an object.

Can someone tell me if this is right, or if I missed any major concepts or points? I'm really just trying to understand why and when you would use each class.

ICustomTypeDescriptor

• Implementing this interface in a class totaly overrides the native properties of a class and replaces them with the PropertyDescriptors returned by ICustomTypeDescriptor.GetProperties()

TypeDescriptionProvider

• Used to extend on the existing properties of a class
• A TypeDescriptionProvider is appended to a class through a TypeDescriptionProvider attribute
• The GetTypeDescriptor() method of the TypeDescriptionProvider returns an ICustomTypeDescriptor to be appended to the existing properties of the type.
• A PropertyGrid will show both the properties of the class found through Reflection, and the properties added to the class through the TypeDescriptionProvider

TypeConverter

• Converts between types
• In terms of using a PropetyGrid used to convert between complex types and primitive types that can be displayed/edited in the property grid.
• The GetStandard values method of a TypeConverter can also be used to show a list of possible values in the propertygrid

UITypeEditor

• Defines a custom editor for manipulating a property of a complex type.
• Associated with a property through an attribute.

So ICustomTypeDescriptor an TypeDescription provider are used to add/change/replace entire properties of objects. TypeConverter and UITypeEditor are applied to individual properties and control how those specific properties are interfaced with.

Answer 1

Tweaks:

• TypeDescriptionProvider

  • still replaces metadata (not extends)
  • can also be added be TypeDescriptor.AddProvider
  • can be applied per-type as well as per-instance, making it possible to apply to lists without having to implement ITypedList

• TypeConverter

  • for PropertyGrid, this is also the mechanism used to obtain metadata; note that ExpandableObjectConverter simply delegates to TypeDescriptor.GetProperties, but this is not always the case
  • also responsible for re-creating immutable objects (such as structs) with changes

• UITypeEditor

  • also responsible for painting the preview box in PropertyGrid

Additional:

• IExtenderProvider - appends properties; this may be what you were getting confused with TypeDescriptionProvider
• ITypedList - broadly the twin of ICustomTypeDescriptor, but for lists; can be avoided by use of TypeDescriptionProvider and a non-object indexer on any IList, i.e. public T this[int index] {get;}
• IListSource - provides indirection between a data-source and the data; for example, a DataTable implements IListSource, returning DefaultView when requested