2e Development Standards - Screen Functions (Part III)

Today we shall take a quick look at the Display File function (DSPFIL).

This is a very commonly used function type in 2e and if my notes are correct there may be a thing or two of interest in this post. However, I guess that this depends on whether you are an ageing old developer like myself or one of the new kids on the block in Bangalore.

But back to the action. Like many other function types the DSPFIL can be used to display data and interact with it in multiple manners. i.e. It can act like an intelligent Select Record and also allow multiple selects. It can also be used to show the contents of an array.

Hold on I hear you say.

"It's a display file and arrays are not files......"

That's true but there are methods to complete this. Nudge me with some comments and I might write up a few examples of code to show you how to achieve this.

Also as the DSPFIL has the CTL (header region) it can be used to provide an interface with a tab look 'n' feel.

Anyhow. Major tip. Take a look at the function options for this function type. In particular, the function option called Re-Process Subfile. Set this on and off and take a look at the action diagram. There will be additional user points and logic added if this is set to Yes. This is just another example of the PODA principle that is taught when you attend training.

PODA stands for Parameters, Options, Design and Action Diagram. The philosphy behind this is simple. The more correct decisions you make at the preceding level i.e. Paramters first, then options (function options) etc the less coding (action diagramming) you will need to do.

2e is quite a neat tool. You should be judging your developers based on the least amount of code required rather than rewarding on a LOC principal (Lines of Code). I think it is fair to say that anyone can write a bad program.

Below are two sections that provide some insight into the function.

General Considerations

The default scan limit is 500. This may not be appropriate for large files. If necessary set the scan limit in USER:Initialise Program to a higher value or even to Maximum. Note: That the scan limit is a model value. If you require a higher number by default (across your model) then I recommend you change the model value YSCNLMT.

Best Practice

Any subfile control selector fields not used should be dropped rather than hidden. This is for performance reasons and avoids the problem of unintentionally deselecting subfile records. To do this simply place enter ‘-‘ against the field from within the EDIT SCREEN FORMAT DETAILS screen.

Multi-part ACP key fields acting as positioners will automatically become selectors if low order fields have data and high order fields are blank. Ensure that you understand the type of data likely to be used for the screen.

Check that the operators used by subfile selectors are appropriate for the function design. Ensure you want EQ, LE, GT or CT for example. Don't assume the default role of these fields.

If a positioner or selector field has mod 10/11 check digit then it may be appropriate to replace with a function field without the check digit. The user does have to enter a valid number to position within a list.

Tip

There is no standard feature to stop the function loading records into the subfile under programmer control. The program continues until subfile page full, scan limit reached or hits end of file. However, you may trick the function to thinking its hit end of file by using a RTVOBJ over the same ACP using a very high key value. This positions the file cursor at end of file.

USER:Process Command Keys has got nothing to do with command keys. Command key processing should normally be added to USER:Process Subfile Control.

Subfile select status field is automatically set to blanks if subfile record processing completes without error.

Gotchas

If F4=Prompt is used on any subfile control selector STS type field then there is no automatic subfile reload and CALC:Subfile Control Function Fields is not executed. User then has to press enter to invoke appropriate selection logic. Function works OK if '?' is used. There is no known workaround for this bug. I would suggest that this is not actually a bug and it is harsh to judge it that way. It is simply because the enter key was pressed for the ? and not the F4 prompt.

CALC:Subfile Record Function Fields is executed before USER:Initialise Subfile Record and therefore you may process a record subsequently deselected. i.e. PGM.*Record Selected.

If any RST input parameter key is also input on device design, and its a file to file relation, then that file validation is deferred until the main validation cycle rather than take place during the load cycle. Any automatic virtuals from the 'Owned by' file will be blank when function is loaded.

An input function field added to RCD format will not automatically check for required value. Even if you set the value to Allow Blank ‘ ‘. This is because the DSPFIL template isn’t designed to have input fields and doesn’t generate the validation routine regardless of how the flag is set or any check conditions. Need to add the code procedurally via the action diagram to force input.

An input function field added to CTL format will not automatically check for required Value. Need to add the check procedurally.

Thanks for reading.
Lee.