Listen to a value change of my text field

You can set a delegate for your NSTextField instance and have the delegate implement the following method:

- (void)controlTextDidChange:(NSNotification *)notification {
    // there was a text change in some control
}

Your delegate object can be the application delegate, a window controller, a view controller, or some other object in your application. The delegate can be programatically set via

[myTextField setDelegate:delegateObject];

or, in Interface Builder, via the delegate outlet available in the NSTextField control.

Note that if there are multiple controls hooked to the same delegate then -controlTextDidChange: will be sent for each control, i.e., the same method is called for different controls. If you want different behaviour according to the control where the text has changed, you can use -[NSNotification object] to identify the control that has sent the notification.

For instance, if you have two text fields with corresponding outlets nameField and addressField, and you’ve set the same delegate for both fields, then:

- (void)controlTextDidChange:(NSNotification *)notification {
    // there was a text change in some control
    // [notification object] points to the control that has sent
    // the notification

    if ([notification object] == nameField) {
        // nameField has changed
    }
    else if ([notification object] == addressField) {
        // addressField has changed
    }
}

Alternatively, you could have one delegate for each text field. In this case, there’d be no need to test [notification object].