WebForm-base app performance problems

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   Here are some introductory remarks on ITypedList:

One cannot add a dynamic property to a type: one can only tell a list that contains instances of that type to report (to whomever asks in the correct manner) that such and such property exists. This is done by writing the list so that it implements the .NET ITypedProperty interface, which mandates that the implementing list include a method called GetItemProperties(). Our lists, and some of the .NET lists, do implement ITypedList; but it is still up to the author of the list class to determine how GetItemProperties() shall decide what it returns.

When a consumer calls GetItemProperties() on one of our lists (BindableList<T>, or a subclass), the method searches a dictionary (again of our making) to see what properties it should tell the caller are available for binding on the contained type.  

For example, suppose our ControlBindingManager designer asks the mEmployees entity list (by calling GetItemProperties() on it), "What properties are available on the Employee type for binding to?"  mEmployees replies, "LastName, FirstName, BirthDate, and SalaryControlBackColor".  LastName, FirstName, and BirthDate are properties that are defined in the Employee class, but SalaryControlBackColor is a property that your code added dynamically (perhaps by calling mEmployees.AddPropertyDescriptor()).  AddPropertyDescriptor() didn't add the property to the Employee type directly -- that can't be done -- instead, it added a PropertyDescriptor representing SalaryControlBackColor to our dictionary of PropertyDescriptors. But anything reflecting directly against the Employee type for a list of properties will find nothing about a SalaryControlBackColor property.

When you code an expression like 

    emp.Manager.LastName,

.NET looks (directly) at the type (Employee) of which emp is an instance to see if that type contains a Manager property. If it does, then it looks at the Manager type to see if it contains a LastName property; and so on down the chain.  If it looks at the Employee type for a "__Manager__LastName" property, it won't find it, because it doesn't exist on the Employee type: it only exists in our dictionary of PropertyDescriptors (where it is indeed associated with the Employee type).  But .NET doesn't know anything about that list: it examines the Employee type directly.

You can find discussion of this in the section "Manipulating the List of PropertyDescriptors for a BindableList(of T)", in Chapter 7 of the Developers Guide.  For a little more information, continuing reading the next section, "Global v. Private PropertyDescriptorList

Now that you understand ITypedList, look at the following proposal to add Nested Properties to the AspDataSource.  This is a proposed feature enhancement:

 uploads/23/typedescriptionprovider.zip

Edited by davidklitzke - 05-Aug-2008 at 1:37pm