Hey, use /eventtrace to track events in the game. Can't check right now, but using that tool you should be able to find which event fires when you join a group.
Here's a list of events:
http://wowprogramming.com/docs/events
Using something like this to catch it:
Lua Code:
local function EventHandler (self, event, ...)
if self[event] then
self[event](self, ...)
end
end
local f = CreateFrame("FRAME", "MyAddon", UIParent)
function f:ADDON_LOADED(...)
-- do stuff when loaded
end
function f:PLAYER_LOGOUT(...)
-- do stuff when you log out
end
function f:PLAYER_STARTED_MOVING(...)
-- do stuff when you start moving
end
f:RegisterEvent("ADDON_LOADED")
f:RegisterEvent("PLAYER_LOGOUT")
f:RegisterEvent("PLAYER_STARTED_MOVING")
f:SetScript("OnEvent", EventHandler)