It sometimes happens that I need to create a screen from which users can choose values intended for a procedure. For example, I developed a program which allows a manager to choose lines from an existing customer order, have those lines inserted into a new order which the program creates, and have the original lines zeroed out.
Why would I need to develop such a screen when from the "input parameters" dialog of a procedure, one can press F6 twice and open the base form of the parameter (e.g. the customers screen, the parts screen)? The reason is that pressing F6 twice can only open what the documentation calls "a root form [screen] (having no upper-level form of its own)". In the above example, data is required from the 'orderitems' table, whose screen is not a root screen (its upper level screen is, of course, the 'orders' screen).
Normally, the way I have solved this in the past is to define a specific table for this task and then develop a screen based on that table. Today I discovered an easier way of solving this problem.
One still has to write a procedure which at the least will consist of two stages, a screen and procedural code, but there is no need to define a specific table upon which the screen will be based. Let's say that I want to re-implement the example which I gave at the beginning. I can define a screen which is based on the 'orderitems' table, showing the fields which I want, along with the parent order number (which will appear on every line). The trick is that the procedure passes to the screen a file parameter, into which will be stored the lines which are displayed on the screen. This file parameter is then passed to the procedural code which acts on the lines in the file (table) - which are the lines which were stored in the screen!
For my own reference, the original example where I found this technique is a procedure called TEC_CALCINVLEVEL, which unfortunately for my readers is not part of standard Priority, but rather was developed in the early days of my company using Priority - before I arrived on the scene. Whoever it was didn't bother in signing their work, let alone documenting it.
I doubt that I'm going to rewrite the various programs of this type which I've already written, but I'll try and bear this technique in mind in the future.