ios - 我向哪个 super View 添加约束重要吗？

Question

假设我有 3 次观看

 A|----------|
  | B|-----| |
  |  | C ▢ | |
  |  |_____| |
  |__________|    

如果我有涉及 View B 和 View C 的约束。

documentation建议添加到 View C 是非法的:

The constraint must involve only views that are within scope of the receiving view. Specifically, any views involved must be either the receiving view itself, or a subview of the receiving view. Constraints that are added to a view are said to be held by that view. The coordinate system used when evaluating the constraint is the coordinate system of the view that holds the constraint.

• 将其添加到 View A 还是 View B 有关系吗？
• 添加到一个 super View 而不是另一个 super View 有什么影响吗？
• 是否有任何便利性影响？ (例如，如果所有约束都集中在一个地方，管理起来会更容易吗？)

Answer 1

• 将其添加到 View A 还是 View B 并不重要，只要它们满足您在文档中引用的要求即可。
• 据我所知，没有任何影响，无论哪种方式布局都是相同的。 根据中的注释，约束不一定会添加到您显式添加它们的 View 中UIView 头文件(参见下面的摘录)它们通常安装在约束中涉及的 View 最近的祖先处(并且 View 被认为是它自己的祖先)。
• 这两种方式本质上都不比另一种更方便(除非您没有对 A 的引用，在这种情况下，将其添加到 B 显然更方便)。这取决于您的应用程序的设置(您有哪些导出/引用等)。 鉴于约束没有安装在您显式添加它们的地方，这两种方法都不会更方便。不过，我认为将它们添加到系统最终安装它们的位置会稍微更有效。

编辑:

此注释来自 UIView.h，位于用于安装约束的方法之上:

/* A constraint is typically installed on the closest common ancestor of the views involved in the constraint. 
 It is required that a constraint be installed on _a_ common ancestor of every view involved.  The numbers in a constraint are interpreted in the coordinate system of the view it is installed on.  A view is considered to be an ancestor of itself.
 */