Executing Callbacks (Menu Event Handlers)

Callbacks tie into menu buttons via the same ACTIONS command used for journals and programs, but differ in two key ways:

1. The menu file does not reference the callback name directly — it references a string that must be registered to the callback via AddMenuAction (C++, VB, C#), addMenuAction (Java), or UF_MB_add_actions (Open C).
2. Callbacks return a value that can terminate the remaining action list for that button.

Callback Return Values

Return Value	Meaning
Continue	Continue performing the menu item's remaining actions
Cancel	User interaction requested inhibiting the menu item's actions
Override Standard	Inhibit further actions because a pre-action replaced the standard action for a standard NX menu item
Warning	Inhibit further actions due to a warning condition
Error	Inhibit further actions due to an error condition

Programmatically, Cancel, Override Standard, Warning, and Error all behave identically — any value other than Continue stops the rest of the action list from executing. The only practical difference is which value gets logged in the syslog.

Example

A sample registers multiple callbacks on a single menu button, where the first callback's returned status controls whether subsequent actions execute. To test: compile the supplied cb_status_test program, place its library in the startup folder with the sample menu file, launch NX, and go to File tab → Open. A dialog prompts "Select a return status" — choosing values other than Continue prevents the STANDARD Open dialog (and any later actions) from running.

Further language-specific implementation details are in the Open C Reference Guide's relevant chapter.

Related Topics

• Programs, Journals, or Callbacks from Existing Menu Items
• Example Menu File with Actions
• Executing Programs
• Executing Journals