1. Basic properties of the container (the most basic class of the container, LayoutProtocol)
(1) doLayout(), which can typeset the child controls in the container;
(2) getLayoutContentSize(), which can get the size of the container;
(3) getLayoutElements(), which can get all the child controls in the container
(4) createLayoutManager(), create a typesetting LayoutManager derived class LinearVerticalLayoutManager (linear vertical), LinearHorizonTalLayoutManager (linear horizontal), RelativeLayoutManager (relational type), etc. (used to layout child controls).
2. The container doLayout process is as follows
(order knowledge https://blog.csdn.net/qq_28290581/article/details/52165343)
