Android: Data --- SharedPreferences

• This is a way to save small ammounts of data.

• Often associated with the concept of User Preferences --i.e. saved login, or specified text color, etc.

• Usefull when you want to save only a little information and don't want overhead of File I/O.

• Saves as name=value pairs in an xml file associated with the specified application package. (default is application_packagename_preferences.xml )

• Uses android.content.SharedPreferences

• Limitation --- only shares data (name/value pairs) across classes in the same Package!!!

What to do

Step 1: somehow get the data in name/value pairs you want to store

Step 2: Inside Activity class use it's getSharedPreferences("<packageName>_preferences", Mode) to get instance of SharedPreferences class, lets call it appPrefs

//inside your ACTIVITY class

SharedPreferences appPrefs = getSharedPreferences("apps_packagename.whatever_preferences", MODE_PRIVATE);


// the above call will create the xml file apps_packagename.whatever_preferences.xml if it does not exist to store data

NOTE: getSharedPreferences(String name, int mode)

Retrieve and hold the contents of the preferences file 'name', returning a SharedPreferences through which you can retrieve and modify its values.

NOTE: MODE_PRIVATE means the xml prefrence file that will get created by this method to store the name/value pairs can only be edited by this application.

 

Step 3: Use aSharedPreferences to grab any already stored value for a particular name

• COMMAND TO GET DATA:           appPrefs.getString("name", "");
  
  • or getInt, getLong ,etc. See API
    
    
    
    
    

Step 4: If you want to store new name/value pairs or modify the values of an already stored pair -----
Get instace of android.content.SharedPreferences.Editor by calling appPrefs.edit();

android.content.SharedPreferences.Editor   prefsEditor = appPrefs.edit();   

Step 5: Use android.content.SharedPreferences.Editor to modify the current Preferences, using Editor.put*("name","value")

• COMMAND TO PUT DATA:           prefsEditor.putString("name","value");
  • or putInt, putLong ,etc. See API
    
    
• COMMAND TO COMMIT TO FILE and puts,etc:        prefEditor.commit(); //until do this file not altered. 
  
• COMMAND TO CLEAR DATA:          prefsEditor.clear(); //clears all stored data

 

Example using Android PreferenceActivity with SharedPreferences for storage

NOTE: this example does not use the default filename package_preferences.xml and instead gives its own name for the xml file