keyboardWillShow not respond

here is problem, when i debug my program, i found keyboardWillShow function not responds every time. just first time, it will be called by program. here is my code, i dont know whats wrong in my code, but, when the keyboard first appeared, the function run well.

- (void)keyboardWillShow:(NSNotification *)notification {

    /*
     Reduce the size of the text view so that it's not obscured by the keyboard.
     Animate the resize so that it's in sync with the appearance of the keyboard.
     */


    NSDictionary *userInfo = [notification userInfo];

    // Get the origin of the keyboard when it's displayed.
    NSValue* aValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];

    // Get the top of the keyboard as the y coordinate of its origin in self's view's coordinate system. The bottom of the text view's frame should align with the top of the keyboard's final position.
    CGRect keyboardRect = [aValue CGRectValue];
    keyboardRect = [self.view convertRect:keyboardRect fromView:nil];

    CGFloat keyboardTop = keyboardRect.origin.y;
    CGRect newTextViewFrame = self.textview.frame;

    newTextViewFrame.size.height = keyboardTop - self.view.bounds.origin.y;

    // Get the duration of the animation.
    NSValue *animationDurationValue = [userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval animationDuration;
    [animationDurationValue getValue:&animationDuration];

    // Animate the resize of the text view's frame in sync with the keyboard's appearance.
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:animationDuration];

    textview.frame = newTextViewFrame;

    [UIView commitAnimations];
 }
- (void)keyboardWillHide:(NSNotification *)notification {

    NSDictionary* userInfo = [notification userInfo];

    /*
     Restore the size of the text view (fill self's view).
     Animate the resize so that it's in sync with the disappearance of the keyboard.
     */
    NSValue *animationDurationValue = [userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval animationDuration;
    [animationDurationValue getValue:&animationDuration];

    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:animationDuration];

//    textview.frame = self.view.bounds;
    [self save];

    [UIView commitAnimations];
}

and i regist notification

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    [[NSNotificationCenter defaultCenter]
     addObserver:self
     selector:@selector(keyboardWillShow:)
     name:UIKeyboardWillShowNotification
     object:nil];
    [[NSNotificationCenter defaultCenter]
     addObserver:self
     selector:@selector(keyboardWillHide:)
     name:UIKeyboardWillHideNotification
     object:nil];

}

and remove it in here

- (void)viewDidUnload
{
    [super viewDidUnload];
    [self save];
    self.textview = nil;
    self.title = nil;
    self.tags = nil;
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];


}

i resign firstresponder, here is my code

- (IBAction)save:(id)sender {
    self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self act开发者_高级运维ion:@selector(addNote)] autorelease];

    [textview resignFirstResponder];


}

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField{
    self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(save:)] autorelease];
    [self setUpUndoManager];

    return YES;


}

- (BOOL)textFieldShouldEndEditing:(UITextField *)textField{
    [self save];
    return YES;

}

Make sure that you are not writing any code to remove observer..... Please provide keyboardWillHide method also....