Android application with the icon as the only user interface

Question

I am currently working on an app which is just a event trigger. I want it to be as simple as possible so I was wondering if it was possible to create an app which works as follows:

When you click on the launcher icon, instead of going into an application, the app's icon merely changes color (e.g. the icon flips from red to green). This would indicate the status of the app. Perhaps if you want to get fancy display a Toast pop-up briefly when it is triggered but nothing more than that. At all times you wold still be in the applications menu.

Answer 1

Add a widget with an icon, then change that icon depending on the tapping of the icon.

Answer 2

I believe that you will find the answer by using ancient wisdom…