how to use shared preferences in multiple fragment files

Question

I need to use shared preferences in multiple fragment files (cant use activity files) I have to store several string lines.

How do I initialize shared preferences in my fragments? How do I write / read to it?

Do I need to initialize it in my main activity or do I have to initialize it in my fragment activity files?

Tricks like:

Context context = getActivity();
SharedPreferences sharedPref = context.getSharedPreferences(getString(R.string.preference_file_key), Context.MODE_PRIVATE); 

... doesn't work.

Answer 1

Try to encapsulate your SharedPreferences in some preferences class, similar to this:

class MyPrefs {

    private static final String FILENAME = "prefs_filename";
    private static final String KEY_SOMETHING = "something";

    private SharedPreferences mPreferences;

    public MyPrefs(Context context) {
        mPreferences = new SharedPreferences(FILENAME, Context.MODE_PRIVATE);
    }

    public void setSomething(Something value) {
       mPreferences.edit().put...(KEY_SOMETHING, value).commit();
    }

    public Something getSomething() {
       return mPreferences.getSomething(key, defaultValue);
    }
}

This way we provide clean API for our non-volatile data storage. SharedPreferences is too low-level, exposing too many details, such as storage file name and it forces us to remember all keys and value types to extract any data. It may work in simple cases, but as soon as your stored data becomes complex, it creates tons of problems. Try storing something like a user profile with few fields or a simple complex number and you'll get the idea. Using raw SharedPreferences will make your refactoring royal pain. Even simple data format upgrade (like schema update) will quickly become impossible with naked SharedPreferences.

Answer 2

Using profiles should be stored in an SQL database, not shared preferences. Hence the name. A database stores data, preferences store preference values. You can't complain about an API when you are misusing it.

Start with SQLite documentation