Caching Solutions

Preferences #

One of the most common ways to persist data on the Android phone is to use SharedPreferences.

The shared preference is basically a key-value store solution for a small amount of data with a built-in memory cache. We already used shared preferences to persist the login state.

Files #

When the data is too big for the shared preference, we can always use plain old files.

String filename = "myfile";
String fileContents = "Hello world!";
try (FileOutputStream fos = context.openFileOutput(filename, Context.MODE_PRIVATE)) {
    fos.write(fileContents.toByteArray());
}

The problem with files is that we need to convert our data to a format that can be stored and reconstructed later, such as a JSON string, which is not efficient in some cases.

SQLite #

Fortunately, in Android we can create a local database - SQLite.

The android.database.sqlite package contains all sorts of API to work with databases - from simple queries to complicated joins. While the Android SQLite package contains everything we need, the API is pretty basic and requires us to write a lot of boilerplate code. For these reasons, Google decided to write an abstraction on top of android.database.sqlite package to make it easier to work with a database.

This layer is available as a separate library called Room. In this chapter we are going to learn how to use the Room database to store and access blog articles.