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Text Editing Programming Guide 
Delegate Messages and Notifications

Although you could alter the text view’s behavior by subclassing the text view and overriding insertText:replacementRange: and doCommandBySelector:, a better solution is to handle the event in the text view’s delegate. The delegate can take control over user changes to text by implementing the textView:shouldChangeTextInRange:replacementString: method.

To handle keystrokes that don’t insert text, the delegate can implement the textView:doCommandBySelector: method.



Note:  To modify editing behavior, your first resort should be to notification or delegation, rather than subclassing. It may be tempting to start by subclassing NSTextView and overriding keyDown:, but that’s usually not appropriate, unless you really need to deal with raw key events before input management or key binding. In most cases it’s more appropriate to work with one of the text view delegate methods or with text view notifications.




NSTextInputContext


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