How to detect Keyboard key pressed in iphone?

Assuming the keyboard is showing as a result of the user tapping on a UITextfield, you can make yourself the delegate and implement this method:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

It will be called every time a user presses a key.

You can directly handle keyboard events every-time a user presses a key:

Swift

For Textfield use following delegate method -

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

}

For TextView use following delegate method -

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

}

Objective C

In case of UITextField

- (BOOL)textField:(UITextField *)textField
          shouldChangeCharactersInRange:(NSRange)range
          replacementString:(NSString *)string {

    // Do something here...
}

In Case of UITextView :

- (BOOL)textView:(UITextView *)textView
      shouldChangeTextInRange:(NSRange)range 
      replacementText:(NSString *)text {

    // Do something here...
}

So every-time one of these method is called for each key you press using keyboard.

You can use NSNotificationCenter also. You only need do add any of these in ViewDidLoad method.

NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];

UITextField :

[notificationCenter addObserver:self
                       selector:@selector(textFieldText:)
                           name:UITextFieldTextDidChangeNotification
                         object:yourtextfield];

Then you can put your code in method textFieldText::

- (void)textFieldText:(id)notification {

    // Do something here...
}

UITextView

[notificationCenter addObserver:self
                       selector:@selector(textViewText:)
                           name:UITextViewTextDidChangeNotification
                         object:yourtextView];

Then you can put your code in method textViewText::

- (void)textViewText:(id)notification {

    // Do something here...
}

Hope it helps .