Skip to content

Writing Custom Controls for ASP.NET

Writing ASP.NET Web Pages showed how you can build ASP.NET web pages by combining APL code with the web controls provided in the .NET namespace System.Web.UI.WebControls. These controls are just ordinary .NET classes. In particular, they are extensible components that can be used to develop more complex controls that encapsulate additional functionality.

This chapter describes how you can build custom server-side controls for deployment in ASP.NET web pages.

A custom control is a .NET class that either inherits from the Control class in the .NET namespace System.Web.UI or inherits from a higher class that is itself based upon the Control class. Like any other .NET class, a custom control is implemented in an assembly, physically as a DLL file. This chapter uses examples to explore different ways to implement a custom control:

  • The Control class provides a Render method whose job is to generate the HTML that defines appearance of the control. The first example, the SimpleCtl control, overrides the Render method to display a simple string "Hello World" in the browser (see Example: The SimpleCtl Control).

  • The TemperatureConverterCtl1 control is an example of a compositional control, that is, one that is composed of other standard controls packaged with special functionality (see Example: The TemperatureConverterCtl1 Control).

  • The TemperatureConverterCtl2 control uses the basic approach of the SimpleCtl control, but provides the same functionality as TemperatureConverterCtl1 (see Example: The TemperatureConverterCtl2 Control).

  • The TemperatureConverterCtl3 control illustrates how to generate events for the hosting page to catch and process (see Example: The TemperatureConverterCtl3 Control).

These examples, which are based on a series of articles called Advanced ASP.NET Server-Side Controls by George Shepherd that appeared in the msdn magazine (October 2000, January 2001 and March 2001 issues), are implemented as Dyalog classes in a namespace called DyalogSamples in the workspace [DYALOG]\Samples\asp.net\temp\bin\temp.dws. The corresponding .NET assembly [DYALOG]\Samples\asp.net\temp\bin\temp.dll) was generated from this workspace. 

      )LOAD "C:\Program Files\Dyalog\Dyalog APL-64 18.2 Unicode\Samples\asp.net\temp\bin\temp.dws"
C:\Program Files\Dyalog\Dyalog APL-64 18.2 Unicode\Samples\asp.net\temp\bin\temp.dws saved Tue Mar  8 13:20:48 2022

      )OBS
DyalogSamples

      )CS DyalogSamples
#.DyalogSamples

      )CLASSES
SimpleCtl       TemperatureConverterCtl1        TemperatureConverterCtl2        TemperatureConverterCtl3