cocoa:add-observer

(cocoa:add-observer target selector &key name object center)

Makes target (an object, or an objc:standard-objc-object) observe the notifications named name (a string) posted by object, nil matching any: selector, a method taking the NSNotification, is sent for each. center defaults to the default notification center. Answers nil. Part of the macOS-only cocoa package -- the interpreter (java -jar, or the rontolisp native binary), a compiled .class / .jar and a --native executable for macOS on Apple silicon, never a .wasm; on a machine without the runtime it signals an error. See the macOS GUI guide.

MY-APP> (define-objc-class watcher ()
          ((seen :initform nil :accessor seen))
          (:objc-class-name "Watcher"))
WATCHER
MY-APP> (define-objc-method ("noticed:" :void) ((self watcher) (note objc-object-pointer))
          (push (invoke-into 'string note "name") (seen self)))
"noticed:"
MY-APP> (defvar *w* (make-instance 'watcher))
*W*
MY-APP> (cocoa:add-observer *w* "noticed:" :name "Ping")
NIL
MY-APP> (invoke (invoke "NSNotificationCenter" "defaultCenter")
                "postNotificationName:object:" "Ping" nil)
NIL
MY-APP> (seen *w*)
("Ping")
MY-APP> (cocoa:remove-observer *w* :name "Ping")
NIL