[Baertram]

Originally Posted by Havin First, thank you, for the quick answer So, im gonna "sniff" it then. Thats not a perfect solution, but it may do the job also. Besides that, does a value exist to find out which of the bars is currently active? That would help to save the Ultimate Costs and to position that information in the screen.

You can use the event if a weapon pair changes:

--Register callback function if the weapon bars change
    EVENT_MANAGER:RegisterForEvent(myAddon.Name .. "_WeaponPairChanged", EVENT_ACTIVE_WEAPON_PAIR_CHANGED, ActiveWeaponPairChanged)

In the callback function "ActiveWeaponPairChanged" you can save the active weapon pair to a variable in your addon:

--Fires each time you change your weapon bars
local function ActiveWeaponPairChanged(eventCode, activeWeaponPair, locked)
    myAddon.activeWeaponBar = activeWeaponPair
end

This event will trigger multiple times if the weapon pair changes!
If I remember right it was something like
-One time for the "form-bar" with locked = true
-One time for the "to-bar" with locked = false
-One time for the "form-bar" with locked = false

Locked is the state as the abilities on the bar get locked. They get grayed out and you're not able to use them during the switch happens.