Working with files and streams

Almost every app needs to persist data. Imagine that you have just downloaded an app and worked with it for a while. The next time you open it, you would like to see that it has remembered what you have done so far. An app can store its data in the cloud, in an embedded database, or in a file. This last option is the easiest to use, and so it’s the one we want to start from.

A local file can store information in different formats. It could be a binary file, which is just an array of bytes that is left to an app to make sense of, or it could be a text file. Your app can store information in plain text or it can use file formats such as JSON or XML to make it easier to process structured information, even if saved as text.

Imagine that you would like to write a small mobile app to keep track of your favorite locations on the internet. To keep it simple, it could be just a list of favorite items made up of two strings: a URL and a caption. Let...