构造事件函数注意点

• (UIViewController *)equalLevelObject {
  //同级别类
  return [UIViewController new];
  }

• (UIViewController *)lowerLevelObject {
  //子级别类
  return [ViewController new];
  }

• (UIViewController *)higherLevelObject {
  //父级别类
  return (UIViewController *)[UIResponder new];
  }

事件函数构建声明实例
事件构建方式***(推荐)***

• (<#基础类/公共父类#> *)<#事件名称#> {
  return <#同级别/子级别类对象值#>;
  }