Question

In Asp.net Web forms why must a user control be partial? I tried to remove the partial keyword and it says:

Missing partial modifier on
declaration of type ‘test’; another
partial declaration of this type
exists

Where is the other declaration?

I am trying to pass a generic type with the user control how can I do that? I can’t unless I change the other declaration too. I couldn’t find it so I removed the partial keyword.

Note:
you do have 3 files if your making WebApplication but if your making website you only get 2 files !

UserControl.ascx
UserControl.ascx.cs 

so in website where is the other declaration ?

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the reason i want generic is because im making a Grid User Control so i want to pass the type the datasource is going to have.

Answer 1

ASP.NET uses partial classes for the codehind because it has to generate all the server side controls you have declared in your ASPX file to a class and merge all the other data files that come along with your codebind. It allow the classes ASP.NET uses to be distributed across multiple files.

From MSDN:

The code file contains a partial
class—that is, a class declaration
with the keyword partial (Partial in
Visual Basic) indicating that it
contains only some of the total code
that makes up the full class for the
page. In the partial class, you add
the code that your application
requires for the page.

This is the key part:

When the page is compiled, ASP.NET
generates a partial class based on the
.aspx file; this class is a partial
class of the code-behind class file.
The generated partial class file
contains declarations for the page’s
controls. This partial class enables
your code-behind file to be used as
part of a complete class without
requiring you to declare the controls
explicitly.

What are you trying to do by adding a generic type to a user control? Can you accomplish this by adding a Type property to the UserControl and then using that?