NSTextView is the front-end component of the Application Kit's text system. It displays and manipulates text laid out in an area defined by an NSTextContainer and adds many features to those defined by its superclass, NSText. Many of the methods that you'll use most frequently are declared by the superclass; see the NSText class specification for details.
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How to detect focus changes in NSTextView objects: http://alienryderflex.com/hasFocus.html
Followup to hasFocus: In the NSTextField page, a couple posters said that my technique is bad because it will waste CPU, and suggested that developers use controlTextDidBeginEditing or becomeFirstResponder instead. I replied as follows: "controlTextDidBeginEditing doesn't fire until the user changes the text. If you want to react to a focus change, it won't work. Also, if you read my article carefully, you'll notice that the polling is based on a timer that fires only 100 times per second. In my tests, this does not significantly tax the processor. I am researching becomeFirstResponder and will followup here. ... Update: I just checked out becomeFirstResponder, and it looks like it might work, but would involve subclassing NSTextField and NSTextView. No big deal, I guess, but neither is comparing a couple of values only 100 times per second. Neither technique would be necessary if the notification system told you when the user clicked in an NSTextField or NSTextView, but for some reason it won't."
See the NSTextField page for more on this topic -- some lively debate and interesting suggestions there. --Darel Rex Finley
Even if you do need to subclass NSTextField/NSTextView you can do it in a generic manner and you'll be able to reuse that code for years to come!
A somewhat hacky but extremely generic technique would be to simply subclass NSResponder, override the method to send a notification, and then use
poseAsClass: so that all responders send that notification.
I am (at long last) learning subclassing and getting rid of my timer. My app will soon use truly zero processor when idle. Hooray! --DarelRex@gmail.com