can’t get correct value of keyboard height in iOS8

With the introduction of custom keyboards in iOS, this problem becomes a tad more complex.

In short, the UIKeyboardWillShowNotification can get called multiple times by custom keyboard implementations:

1. When the Apple system keyboard is opened (in portrait)
   • UIKeyboardWillShowNotification is sent with a keyboard height of 224
2. When the Swype keyboard is opened (in portrait):
   • UIKeyboardWillShowNotification is sent with a keyboard height of 0
   • UIKeyboardWillShowNotification is sent with a keyboard height of 216
   • UIKeyboardWillShowNotification is sent with a keyboard height of 256
3. When the SwiftKey keyboard is opened (in portrait):
   • UIKeyboardWillShowNotification is sent with a keyboard height of 0
   • UIKeyboardWillShowNotification is sent with a keyboard height of 216
   • UIKeyboardWillShowNotification is sent with a keyboard height of 259

In order to handle these scenarios properly in one code-line, you need to:

Register observers against the UIKeyboardWillShowNotification and UIKeyboardWillHideNotification notifications:

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

Create a global variable to track the current keyboard height:

CGFloat _currentKeyboardHeight = 0.0f;

Implement keyboardWillShow to react to the current change in keyboard height:

- (void)keyboardWillShow:(NSNotification*)notification {
   NSDictionary *info = [notification userInfo];
   CGSize kbSize = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
   CGFloat deltaHeight = kbSize.height - _currentKeyboardHeight; 
   // Write code to adjust views accordingly using deltaHeight
   _currentKeyboardHeight = kbSize.height;
}

NOTE: You may wish to animate the offsetting of views. The info dictionary contains a value keyed by UIKeyboardAnimationDurationUserInfoKey. This value can be used to animate your changes at the same speed as the keyboard being displayed.

Implement keyboardWillHide to the reset _currentKeyboardHeight and react to the keyboard being dismissed:

- (void)keyboardWillHide:(NSNotification*)notification {
   NSDictionary *info = [notification userInfo];
   CGSize kbSize = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
   // Write code to adjust views accordingly using kbSize.height
   _currentKeyboardHeight = 0.0f;
}