Code Behind

A Web Form is an ASP.NET page with controls. Web Forms break user interface (UI) programming into business logic and content presentation in much the same way that Visual Basic separates the form of a VB-based Windows application from the code that interacts with it. The presentation file, or Web Forms page, is a container for a mixture of static HTML and ASP.NET server controls. The logic or programming code that interacts with the events generated by the Web Forms page is referred to as the “code-behind” page. The extension .aspx.vb or .apsx.cs indicates whether the page contains Visual Basic.NET or C# code. These code-behind pages are compiled into Dynamic Link Libraries (DLLs), a technique that contributes to the improved performance of ASP.NET.

When a user requests the page, ASP.NET displays the Web Form. When a user selects a control (for example, by clicking on the Submit button), the page is posted back to ASP.NET with information about which control was activated, and ASP.NET executes the associated event-handler from the code.