平时使用 [self.view addSubview:<#(nonnull UIView *)#>]过多 今天首次尝试 addChildViewController 即直接添加子视图控制器
涉及三个VC ParentViewController、OrangeViewController、PurpleViewController
话不多说 直接上代码
主要是 ParentViewController代码

• (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  self.view.backgroundColor=[UIColor grayColor];
  // 初始化控制器
  [self controllersInit];

  // 初始化要展示的区域
  [self showViewInit];

  // 初始化按钮
  [self buttonConfig];
  }

pragma mark - 初始化控制器

• (void)controllersInit
  {
  // 初始化两个控制器并作为root控制器的subController
  _orangeVC = [OrangeViewController new];
  [self addChildViewController:_orangeVC];
  [_orangeVC didMoveToParentViewController:self];

_purpleVC  = [PurpleViewController new];
[self addChildViewController:_purpleVC];
[_purpleVC didMoveToParentViewController:self];
[_purpleVC.view setFrame:self.view.bounds];

}

pragma mark - 初始化要展示的区域

• (void)showViewInit
  {
  // 初始化要展示的区域
  self.showView = [UIView new];
  self.showView.frame = CGRectMake(0, 0, SCR_WIDTH, SCR_HEIGHT - downHeight - 10);
  self.showView.layer.masksToBounds = YES;
  [self.view addSubview:_showView];

  // 将第一个控制器的view添加进来展示
  [self.showView addSubview:_orangeVC.view];

  showVC = _orangeVC;
  }

pragma mark - 初始化按钮以及按钮事件

• (void)buttonConfig
  {
  UIButton *firstVCButton = [UIButton new];
  [self.view addSubview:firstVCButton];
  firstVCButton.backgroundColor = [UIColor purpleColor];
  firstVCButton.tag = 1000;
  firstVCButton.frame = CGRectMake(0, SCR_HEIGHT - downHeight, SCR_WIDTH / 2, downHeight);
  [firstVCButton addTarget:self
  action:@selector(buttonsEvent:)
  forControlEvents:UIControlEventTouchUpInside];

  UIButton *secondVCButton = [UIButton new];
  [self.view addSubview:secondVCButton];
  secondVCButton.backgroundColor = [UIColor orangeColor];
  secondVCButton.tag = 2000;
  secondVCButton.frame = CGRectMake(SCR_WIDTH / 2, SCR_HEIGHT - downHeight, SCR_WIDTH / 2, downHeight);
  [secondVCButton addTarget:self
  action:@selector(buttonsEvent:)
  forControlEvents:UIControlEventTouchUpInside];
  }

• (void)buttonsEvent:(UIButton *)button
  {
  if (button.tag == 1000)
  {
  if (showVC == _orangeVC)
  {
  return;
  }

    [self transitionFromViewController:showVC
                      toViewController:_orangeVC
                              duration:0.5
                               options:UIViewAnimationOptionTransitionNone
                            animations:^{
  
  
  
                            }
                            completion:^(BOOL finished) {
                                showVC = _orangeVC;
                            }];
  

  }

  if (button.tag == 2000)
  {
  if (showVC == _purpleVC)
  {
  return;
  }

    [self transitionFromViewController:showVC
                      toViewController:_purpleVC
                              duration:0.5
                               options:UIViewAnimationOptionTransitionNone
                            animations:^{
  
  
                            }
                            completion:^(BOOL finished) {
                                showVC = _purpleVC;
                            }];
  

  }

}

OrangeViewController、PurpleViewController 仅仅设置了背景色 多多担待