Unfortunately, the validation and handling of input in an application is often an afterthought in the design process. These should be at the forefront of your thoughts during the second round of drafts for the user interface. A touchscreen device offers many more opportunities to streamline the capturing of data from the user, in many cases removing the need for sanitation or validation, while at the same time massively improving the user's experience with the application.
Android provides an excellent toolset to capture many different types of data from the user, while also providing loose coupling between your application components in the form of
Intent structures. By using several smaller