KeyListener in Objective-c

I'm new objective-c. I want to change button image if the textfields are filled. How do we understand a textfield input from the keyboard? KeyListener is using in java, how do we do in objective-c? Than开发者_如何学运维ks

Learn about notifications in Objective-C.

http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/Reference/Reference.html

If programming for iOS, then learn about UIControlEvents.

What you are looking for is a UITextFieldDelegate protocol. A protocol is roughly the same as an interface in Java. The main difference is that methods in protocols can be optional, whereas all methods in a Java interface is always required.

You could implement one or more of these methods:

- (void)textFieldDidBeginEditing:(UITextField *)textField {
   // Do something when the user begins editing
}

- (void)textFieldDidEndEditing:(UITextField *)textField {
   // Do something when the user is done editing
}

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
  // Text field is about to change it's text.
  // Return YES to allow this change
  // Return NO to block this change
}

Many classes in iOS have a corresponding delegate class. For example:

• UITextField & UITextFieldDelegate
• NSXMLParser & NSXMLParserDelegate
• CLLocationManager & CLLocationManagerDelegate

So it is wise to look for the delegate counterpart in the documentation first when you want to listen to, or change the behavior of, an object instance.