How you accept input from your users, and how you validate that input plays a crucial part in the overall experience your users will have with your application. Software should help the users along and tell them what it expects at each step. This not only makes an application easier to use, but also much faster to work with.
ListItemSelectionActivity, will often help your users trawl through large data sets, while protecting them from making a choice that they don't want to, or is invalid. It's a very commonly used type of widget and is seen in many different applications (in various forms). Android, at present, doesn't have a generic class to perform this job quite as easily.
In the next chapter, we'll start taking a look at a ...