- (void)viewDidLoad {
    [super viewDidLoad];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardDidShow:)
                                                 name:UIKeyboardDidShowNotification
                                               object:nil];
}

- (void)findCandidateBar:(NSArray *)subviews {
    for (UIView *view in subviews) {
        if ([[view description] hasPrefix:@"<UIKeyboardCandidateBar"]) {
            _candidateBarHeight = view.frame.size.height;
        } else {
            [self findCandidateBar:[view subviews]];
        }
    }
}

- (void)keyboardDidShow:(NSNotification *)notification {
    _candidateBarHeight = 0;
    [self findCandidateBar:[[UIApplication sharedApplication] windows]];

    // ...
}