Are there any documented restrictions or limitations on the use of global functions used in DataWindow expressions, where the global functions utilize non-visual objects (NVO's) and a DataStore?
Background:
I'm experimenting with global functions that analyze and encode string data to produce a variety of one-dimensional barcode styles (such as a UPC barcode) in a DataWindow, using TrueType barcode fonts. My goal is to be able to directly produce these barcodes in DataWindows utilizing these global functions in an expression contained within a computed field DWObject, eliminating the need to perform the necessary data encoding in a separate step in the application.
For most barcode styles, the data encoding steps are relatively simple. The steps can be coded in PowerScript within one or two global functions, and the computed field expressions work flawlessly to produce a barcode. However, GS1-128 barcodes are a different animal.
The GS1-128 barcode specification supports fields/records (called Application Identifiers, or AI's) within a single barcode. Each AI begins with a numeric prefix, followed by additional character and/or digit sequence(s). There are over 200 defined AI's, each with its own layout, so the parsing, validation, and encoding of GS1-128 data is considerably more complex than what is needed for other 1D-barcodes. I've created a DataStore for the AI definitions that has self-contained data (no data retrieval is needed) that is used in the data parsing and validation steps.
Problem:
Whenever a DataWindow expression that uses these GS1-128 barcode global functions is evaluated, PowerBuilder briefly hesitates, then goes POOF and terminates without any error messages. I suspect the DataWindow expression evaluator is blowing a gasket due to the creation and/or use of the pre-loaded DataStore, or the creation of the NVO's that contain the parsing, validation, and encoding logic, but at this stage that's only a guess on my part.
Question:
I realize these conditions are fairly unique. Has anyone ever successfully utilized a DataStore or other manually-instantiated non-visual objects in a global function that is referenced in a DataWindow expression? Any tips, suggestions or experiences are welcomed and appreciated.
John
The app I've been toying with is eventually destined for CodeXchange - It's primary purpose is to illustrate how 1D-barcodes can be generated by using a TrueType font and some PowerScript code to perform the data encoding and checksum calculations for a healthy variety of common barcode styles, so I'm not anticipating there will be 1000's of barcodes being created and the potential performance issue(s) that could arise from that. Adding multitasking and a brokering interface is overkill in this particular instance, but I can see where that might be a solid approach for heavy-duty, "real-world" types of applications.
Given that PB currently goes kablooey (that's a highly technical software engineering term, by the way) with the current implementation, I'll refactor the GS1-128 barcode support and perform the data encoding from a window and then pass the encoded data and human-readable-text for each barcode into the DataWindow. On the plus side, this will show an alternative way to encode and display a 1D-barcode from the other barcode styles that have already been implemented.
I really appreciate you taking the time to share your suggestions... Thank you!
That is sounds like a very "Kool" project App! All the best of luck with it. We'll be interested to see it in action. ;-)
Regards ... Chris
One thing that I like with your posts - comments it's that it isn't just about programming. :-)
Andreas.