Improve independence of controller from the service?

[defagos]

Currently, the Letterbox service is referenced from the controller implementation. This instantiates the service lazily, performing a system-wide setup (e.g. remote controls) which could interfere with another setup made elsewhere by another component (or a client app itself using the controller only).

We could think about a way to use the Letterbox controller only, avoiding such potential conflicts.

This requirement was made by the Couleur3 team.