Activity at the correct granularity is an important part of your user interface design process. Although it's not a graphical part directly, it defines how the system will interact with your application, and thus how the user will interact with it.
It's a good idea to keep implicit intents in mind when structuring how your
Activity will be started. Creating a generic
Activity allows for other applications to integrate seamlessly with your own, effectively turning your new application into a platform for other developers to work with. An implicitly started
Activity can be replaced or extended by another application, or it can be re-used in other application. In both cases, the user becomes free to customize your application ...