my question is not about the design/coding practices used to write a new alternative keyboard for Android. I'd like only to focus on "attaching it to the system".
In other words:
We know alternative soft keyboards like "BetterKeyboard", "ShapeWriter" etc. They are installed on the phone and the user can (via Settings -> Locale & Text) enable it or not.
How is this behavior obtained?
How to install an application in order to be a substitute of the default keyboard?
Imagine we could write a good activity with a nice GUI and user experience for a keyboard. Now, how can I install it in a way that a user could use it as an alternative keyboard, as BetterKeyboard does?
I hope my question is clear...! Bye