How to dynamically create fb instances during runtime on a plc?

Question

I'm new to PLC programming and we need to create a library for a project. We need dynamically created function block instances during the runtime. There is a concept described on the codesys homepage: https://help.codesys.com/webapp/fb_factory;product=LibDevSummary;version=3.5.15.0

We tried to implement the example but without success. Unfortunately, there is no further information about the concept on the codesys homepage. Has anybody some advice how to dynamically create fb instances during the runtime on a plc?

Answer 1

I made a simple classic OOP Person, Teacher, Student example, here's a project file, or PLCOpenXML file. Basically, changing the value of numberOfTeachers inside PLC_PRG will cause the reinitializarion of the array people with the first numberOfTeachers entries being Teachers, and the rest being Students. You can look at the Device Logs where I write messages for creation/destruction of Teacher/Studemt.

PS. I am myself still exploring the possibilities of the Factory Design in CODESYS, so excuse me if I made any mistakes!

Update 23-03-16: Incorporated the suggested changes by ohraaa

Answer 2

When you want to create an instance of an FB dynamically you need first to put the following attribute above the FB-Declaration:

{attribute 'enable_dynamic_creation'}

Then you must make sure you are not calling __NEW(FB_NAME) cyclically.

Then you assign the result of __NEW(FB_NAME) to a pointer:

//Put this is the declaration section   
pfbName : POINTER TO FB_NAME;
//Your call to create a dynamic instance
pfbName := __NEW(FB_NAME);

If your pointer = 0 after __NEW returns, it means __NEW failed to allocate memory.