ASP.NET Cookbook

5.1. Combining HTML Controls in a Single Custom Control

Problem

You want to create a custom control that combines two or more HTML controls.

Solution

Use the .NET language of your choice to:

1. Create a class that inherits from the Control class in the System.Web.UI namespace.

2. Override the Render method to have it output the HTML controls you wish to include.

3. (Optional) Use the HtmlTextWriter class to enhance your chances of writing well-formed HTML.

To use the custom control in an ASP.NET page:

1. Register the assembly containing the control.

2. Insert the tag for the custom control anywhere in the page.

Figure 5-1 shows the output of a custom control that combines a label and text box. Example 5-1 and Example 5-2 show the VB and C# class files for the custom control. Example 5-3 shows how to use the custom control in an ASP.NET page.

Figure 5-1. Basic custom control output

Discussion

To create a custom control that combines the functionality of two or more HTML controls, you first create a class that inherits from the Control class in System.Web.UI. The Control class is the base class that all ASP.NET server controls inherit from. It provides all of the basic properties, methods, and events necessary to build custom controls.

The only method of Control that is required to output HTML is the Render method. Render is responsible for writing the HTML that will be rendered by the browser. To enhance ...