iPad ModalView表示の時、キーボードが隠れない

@try
{
    Class UIKeyboardImpl = NSClassFromString(@"UIKeyboardImpl");
    id activeInstance = [UIKeyboardImpl performSelector:@selector(activeInstance)];
    [activeInstance performSelector:@selector(dismissKeyboard)];
}
@catch (NSException *exception)
{
    NSLog(@"%@", exception);
}