Persisting Data to the Device

Overview

The Android framework offers several options and strategies for persistence:

• Shared Preferences - Easily save basic data as key-value pairs in a private persisted dictionary.
• Local Files - Save arbitrary files to internal or external device storage.
• SQLite Database - Persist data in tables within an application specific database.
• ORM - Describe and persist model objects using a higher level query/update syntax.

Shared Preferences

Settings can be persisted for your application by using SharedPreferences to persist key-value pairs:

SharedPreferences pref =   
    PreferenceManager.getDefaultSharedPreferences(this);
String username = pref.getString("username", "n/a"); 

SharedPreferences can be edited by getting access to the Editor instance:

SharedPreferences pref =   
    PreferenceManager.getDefaultSharedPreferences(this);
Editor edit = pref.edit();
edit.putString("username", "billy");
edit.putString("user_id", "65");
edit.commit(); 

Local Files

Android can read/write files to internal as well as external storage. Applications have access to an application-specific directory where preferences and sqlite databases are also stored. Every Activity has helpers to get the writeable directory. File I/O API is a subset of the normal Java File API.

Writing files is as simple as getting the stream using [openFileOutput method](http://developer.android.com/reference/android/content/Context.html#openFileOutput(java.lang.String, int) and writing to it using a BufferedWriter:

// Use Activity method to create a file in the writeable directory
FileOutputStream fos = openFileOutput("filename", MODE_WORLD_WRITEABLE);
// Create buffered writer
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fos));
writer.write("Hi, I'm writing stuff");
writer.close();

ActiveAndroid ORM

References

• http://developer.android.com/guide/topics/data/data-storage.html
• http://developer.android.com/training/basics/data-storage/index.html
• http://mobile.tutsplus.com/tutorials/android/data-management-options-for-android-applications/
• http://developer.android.com/reference/android/content/SharedPreferences.html