The premise of making functions is to design first and then realize
mind Mapping
analyze
This function is relatively simple, and there is nothing complicated in the design. The main point is that data is transferred between menus at all levels . It is easy to understand this point and make it.
Implementation process
from big to small
main menu
A menu
Secondary menu
The first time I wrote it was relatively simple, and there were many bad places
A simple video version tutorial will be released later. Fix some problems