Only member functions and variables that are used in the HTML template need to be made public. The rest can remain private. You also must make any variables declared via @Input or @Output or @ViewChild public. The good news is that if you forget to make any of these public, when you run npm run build in the home directory of a project based on a stock project started with ionic start --v2 then you will get a compiler complaint about the variable being private and you can change those one by one until all your complaints go away.
5 Likes