//監聽點擊鍵盤彈出
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(keyboardWithShow:) name:UIKeyboardDidShowNotification object:nil];
    //監聽鍵盤隱藏
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(keyboardWithHidden:) name:UIKeyboardWillHideNotification object:nil];
    
}
#pragma mark - 鍵盤處理
-(void)keyboardWithHidden:(NSNotification *)note
{
    //鍵盤回到屏幕下方時修改約束
    self.bottomSpacing.constant = 0;
    //彈出鍵盤用的時間
    double duration =[note.userInfo [UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    //添加動畫效果
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}
-(void)keyboardWithShow:(NSNotification *)note
{
    //取出鍵盤最終的frame
   CGRect rect = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    self.bottomSpacing.constant = rect.size.height;
  double duration =[note.userInfo [UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];

-(void)dealloc
{
    //刪除所有通知，在頁面銷毀的時候需要移除通知
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}
}