This means that any variable, method or field generated in the file can be used from the cs code-behind file (just as if it was declared in the code-behind file itself).For example, within the Page_Load event handler we could easily add the below code that uses the "Label1" and "Calendar1" control: This will compile clean and run just fine -- because the "Label1" and "Calendar1" field references have been defined within the file. VS 2005 uses a code-behind model conceptually the same as VS 2003.
Visual studio 2010 not generating new control definitions in designer file Visual Studio 2010 Designer File Not Updating This seems to me to be related to the Application Page template, as the Designer works fine for user controls in the same project, and the Application Page template doesn't allow Design View. here is a trick for this little problem: add a user control to your project.
The other partial class file is then a tool-generated/maintained file that contains the protected control field declarations and the other design-time code that Visual Studio requires.
The benefit of splitting them out into two separate files at design-time is that it ensures that the code that VS creates and maintains never interferes (or deletes) code that a developer writes.
The designer and code behind pages are a function of the root aspx page so the designer is not a function of the code behind and thus appears at the same level. User Grid, is it during the build process, or when you attempt to view the page after a build.
If you are viewing the page after a build and getting this error it is exactly correct.