Check if the event is registered or not

[NhuTruong_BeyCons]

Hi all, how to check if a registered event will not register or delete the previous registration event to register a new event, if there is no event in the document, register new. Thank you.

[jeremytammik]

I am not aware of any method to check whether the event has already been registered or not.

You can register it using the `+-` operator and unregister again using `-=`.

I normally keep track of the registration state using a a Boolean variable or by switching some variable between a non-null initialised state and `null`.