Shared Preferences Basics

Introduction
        Android Storage can be done in many ways and one of the way is shared preferences.Shared Preferences allows us to manage session.Since Session are useful when you want to store user data globally through out the application. This can be done in two ways. One is storing them in a global variables and second is storing the data in shared preferences. 

Shared Preferences..What it is? 
    Shared Preferences is an API from Android SDK to store and retrieve application preferences. Shared Preferences are simply sets of data values that stored persistently. Persistently which mean data you stored in the Shared Preferences are still exist even if you stop the application or turn off the device. SharedPreferences available at the Activity level or shared across all Activity in application package.

Shared Preferences are used in android to store some data presistently(i.e. after closing of application, it will persist).If you want to store few amount of data then you can go for Shared Preferences rather than going for Sqlite and all.In that case Shared Preferences are useful.

When to use Shared Preferences ?
1.You can use SharedPreferences to save any primitive data: booleans, floats, ints, longs, and strings. This data will persist across user sessions (even if your application is killed).

2.Think of a situation where you wanna save a small value (a flag probably) that you wanna refer later sometime when user launches the application. Then shared preference comes into action.
You may ask, why we can do it using sqlite too right? But the problem of sqlite is that it’ll want you to write lengthy codes and supporting classes. Shared Preference let you read and write values in couple of lines easily. But always remember, shared preference is not a solution for you to keep complex relational data.

(check also basic SqlLite Database )
How to Intialize?  

     Application shared preferences can be fetched using getSharedPreferences() method.You also need an editor to edit and save the changes in shared preferences. The following code can be used to get application shared preferences.

SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", 0);
 // 0 - for private mode

Editor editor = pref.edit();

How to Store Data In Shared Preference? 

You can save data into shared preferences using editor. All the primitive data types like booleans, floats, ints, longs, and strings are supported. Call editor.commit() in order to save changes to shared preferences. 

editor.putBoolean("key_name", true); // Storing boolean-true/false

editor.putString("key_name", "string value"); // Storing string

editor.putInt("key_name", "int value"); // Storing integer

editor.putFloat("key_name", "float value"); // Storing float

editor.putLong("key_name", "long value"); // Storing long
editor.commit(); // commit changes

How to retrieve Data From Shared Preferences ?
    Data can be retrived from saved preferences by calling getString() (For string) method. Remember this method should be called on Shared Preferences not on Editor.

// returns stored preference value

// If value is not present return second param value - In this case null




pref.getString("key_name", null); // getting String

pref.getInt("key_name", null); // getting Integer

pref.getFloat("key_name", null); // getting Float

pref.getLong("key_name", null); // getting Long

pref.getBoolean("key_name", null); // getting Boolean

And finally how to Clear / Delete Data from shared Preference?

       If you want to delete from shared preferences you can call remove(“key_name”) to delete that particular value. If you want to delete all the data, call clear()

editor.remove("name"); // will delete key name

editor.remove("email"); // will delete key email

editor.commit(); // commit changes

Following will clear all the data from shared preferences

editor.clear();

editor.commit(); // commit change

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