Hi there! I wanna swap button in the tool bar of my iOS chat app.Is there api for that from sdk, or I should do it on my own using custom ui and delegate methods from sdk? 

I need to make an Event field mandatory for all users who DO NOT have the Partner Community User.

I came up with this formula

AND(ISPICKVAL(ISNULL(Event__c ), 
$Profile.Name <> "Partner Community User"))

I get an error the following error.

Error: Field Event__c is a picklist field. Picklist fields are only supported in certain functions. Tell me more

Anuy ideas?