Avoid duplicated instance list code by using a 'Controller'

If you have filters and command handlers then you may end-up with duplicated instance list code.

This may be annoying if a designer decides to change the key structure or additional columns that are used in an instance list, because you have to change all the filters to use the new instance list format.

To avoid this centralize all instance list manipulation code into one Visual LANSA reusable part that all your filters share. Methods in that reusable part can be passed VF_AC007 (VLF-WIN) and VF_AC0007O (VLF-ONE) filter references. This allows a method to act exactly as if it was part of the filter. 

Typically such a central reusable part is called a controller – and is declared as a scope(*Application) object in all other programs that need to communicate with it. 

The shipped VLF-ONE component DF_EMCTLO is an example of a simple controller. Several of the demonstration components use it to handle common interfacing to the PSLMST and PSLSKL demonstration database tables on the server.