+=(_:_:)
public func +=<T>(event: Event<T>, handler: @escaping (AnyObject, T) -> Void) -> Int
Attaches and detaches event handlers.
Parameter
Parameter event: An event that uses event arguments of type T.Parameter
Parameter handler: The handler for this event, which can be sent by any object and uses event arguments of type T.
Returns
An integer, which represents a unique id number for this event.