cocoa - Text change notification for an NSTextField

Question

I would like to use the code from the answer to this question: How to observe the value of an NSTextField on an NSTextField in order to observe changes on the string stored in the NSTextField.

[[NSNotificationCenter defaultCenter]
    addObserverForName:NSTextViewDidChangeSelectionNotification
    object:self.textView 
    queue:[NSOperationQueue mainQueue] 
    usingBlock:^(NSNotification *note){
    NSLog(@"Text: %@", self.textView.textStorage.string);
}];

The class used here is an NSTextView. I can't find a notification in NSTextField to use instead of NSTextViewDidChangeSelectionNotification.

Is there a notification available in NSTextField that can be used in this case ?

Answer 1

If you just want to detect when the value of a text field has changed, you can use the controlTextDidChange: delegate method that NSTextField inherits from NSControl.

Just connect the delegate outlet of the NSTextField in the nib file to your controller class, and implement something like this:

- (void)controlTextDidChange:(NSNotification *)notification {
    NSTextField *textField = [notification object];
    NSLog(@"controlTextDidChange: stringValue == %@", [textField stringValue]);
}

If you're creating the NSTextField programmatically, you can use NSTextField's setDelegate: method after creation to specify the delegate:

NSTextField *textField = [[[NSTextField alloc] initWithFrame:someRect] autorelease];
[textField setDelegate:self]; // or whatever object you want

Delegation is one of the fundamental design patterns used throughout Cocoa. Briefly, it allows you to easily customize the behavior of standard objects (in this case, user interface objects) without the complexity involved in having to subclass the object to add that additional behavior. For example, another lower-level way to detect when the text in a textfield has changed might be to create your own custom NSTextField subclass in which you override the keyDown: method that NSTextField inherits from NSResponder. However, subclassing like that is difficult because it can require that you have an intimate knowledge of the object's inheritance hierarchy. For more info, definitely check out the following:

Cocoa Fundamentals Guide: Delegates and Data Sources

Regarding what id <NSTextFieldDelegate> means: it means a generic object (id) that declares itself as conforming to the <NSTextFieldDelegate> protocol. For more info on protocols, see The Objective-C Programming Language: Protocols.

Sample GitHub project at: https://github.com/NSGod/MDControlTextDidChange