In B4XPages, 'Main' is where almost all platform differences are magically compensated for. Therefore there are 3 completely different 'Main' s.
When you open the project and go to each platform, the 'Main' part is different.
That means that all the common work must be done in instances of B4XPages classes.
The first and only instance of B4XMainPage (instance is 'B4Xpages.MainPage') is the common entry point to the project.
Here you can set constants in 'Sub Class_Globals' or read parameter files. If you declare a variable XXX as Public in the Class_Globals of
B4XMainPage., you can access it any with B4Xpages.MainPage.XXX from anywhere in your project.
[Warning: obfuscation (your own or the built-in method of the IDE) does not protect against persistent hackers]