How to: CoC extension classes

Goal: add behavior to a stock method without touching Microsoft’s class — a chain-of-command wrapper that compiles clean on the first build.

Time: ~10 minutes · Requires: a D365 VM for the build step.

Prerequisites

• A custom model referencing the model that owns the target class (ApplicationSuite for most stock classes — see create & manage a model).
• The target class and method identified (find-references first if you’re unsure who else wraps it).

Steps

1. Find the target class in the AOT explorer; right-click it → New X++ Object → class extension.

2. Review the scaffold — the Studio generates:

   [ExtensionOf(classStr(YourTargetClass))]
   final class YourTargetClass_Extension
   {
       public int totalQty()
       {
           int ret = next totalQty();
           // your behavior here
           return ret;
       }
   }

   The [ExtensionOf(classStr(...))] attribute, the _Extension naming law, and the next-calling stub are all generated — you fill in behavior.

3. Save (Ctrl+S) — the file lands in <root>/<Model>/<Module>/AxClass/ and re-indexes immediately.

4. Build the model (Ctrl+B).

EDITOR · GENERATED COC WRAPPERReal UI capture pendingxpp-coc-scaffold

Verify it worked

• First build: 0 errors / 0 warnings with no hand-fix — the wrapper’s shape is compiler-proven.
• At runtime, your code runs around the stock method (next chains to the rest of the pipeline — Microsoft’s and any other extensions’).

If it goes wrong

• “Class extension … must be final” — you removed final; the attribute pair is load-bearing, restore the scaffold’s declaration exactly.
• Your method never fires — signature drift: the wrapper’s signature must match the target method exactly. Re-generate from the scaffold instead of hand-typing.

Next: table extensions · event handlers.