What is the difference between a Web User Control and a Web Custom Control?

Web custom controls are compiled components that run on the server and encapsulate the user-interface and other related functionality into reusable packages. They can include all the design-time features of standard ASP.NET server controls, including full support for Visual Studio design features such as the Properties window, the visual designer, and the Toolbox. There are several ways to create Web custom controls:

You can compile a control that combines the functionality of two or more existing controls. For example, if you need a control that encapsulates a button and a text box. You can create it by compiling the existing controls together.

If an existing server control almost meets your requirements but lacks some required features, you can customize the control by deriving from it and overriding its properties, methods, and events. If none of the existing Web server controls (or their combinations) meet your requirements, you can create a custom control by deriving from one of the base control classes. These classes provide all the functionality like other Web server controls. You only need to write the logic for the programming features you require.

If none of the existing ASP.NET server controls meet the specific requirements of your applications, you can create either a Web user control or a Web custom control that encapsulates the functionality you need.

The main difference between the two controls lies in ease of creation vs. ease of use at design time. Web user controls are easy to make, but they can be less convenient to use in advanced scenarios. Web user controls can be developed almost exactly the same way that you develop Web Form pages.

Like Web Forms, user controls can be created in the visual designer or they can be written with code separate from the HTML. They can also support execution events. However, since Web user controls are compiled dynamically at run time they cannot be added to the Toolbox and they are represented by a simple placeholder when added to a page.

This makes Web user controls harder to use if you are accustomed to full Visual Studio .NET design-time support, including the Properties window and Design view previews. Also the only way to share the user control between applications is to put a separate copy in each application, which takes more maintenance if you make changes to the control.

Web custom controls are compiled code, which makes them easier to use but more difficult to create. Web custom controls must be authored in code. Once you have created the control you can add it to the Toolbox and display it in a visual designer with full Properties window support and all the other design-time features of ASP.NET server controls. In addition you can install a single copy of the Web custom control in the global assembly cache and share it between applications, which make maintenance easier.

Written by Sandeep Mogulla, Webmaster at www.startvbdotnet.com

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