Absent from the above is all the OTHER things that must happen to get a trigger callback.
Start with the requirements as outlined in the docs for the flavor(s) of OnTrigger you want.
ALSO, for future reference:
If you post a code snippet, ALWAYS USE CODE TAGS:
How to use code tags: Using code tags properly
- Do not TALK about code without posting it.
- Do NOT post unformatted code.
- Do NOT retype code. Use copy/paste properly using code tags.
- Do NOT post screenshots of code.
- Do NOT post photographs of code.
- ONLY post the relevant code, and then refer to it in your discussion.