Android provides many ways of storing data of an application. One of this way is called Shared Preferences. Shared Preferences allow you to save and retrieve data in the form of key,value pair.

In order to use shared preferences, you have to call a method getSharedPreferences() that returns a SharedPreference instance pointing to the file that contains the values of preferences.

Initialization
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 = context.getSharedPreferences("MyPref", 0); // 0 - for private mode
  Editor editor = pref.edit();

Storing Data
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

Retrieving Data
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

Clearing / Deleting Data
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 changes

Ex1 Create a new project.
In the activity_main xml, add an edit text, and 2 buttons and a textView like in the picture.

Ex2 Create a class named MySharedPreference and add the code below:

 public class MySharedPreference {
    SharedPreferences settings;
    SharedPreferences.Editor editor;
    
    public MySharedPreference (Context context) {
      //TODO
    }
    
    public void save(String text){
       //TODO
    }
    
    public String getValue(){
       //TODO
    }
    
    public void clearSharedPreferences(){
       //TODO
    }
 }

TODO:
- In the constructor, Initialize SharedPreferences.
- In the same function, put the given String in the editor. Do not forget to commit
- In the getValue function take the string from the Shared Preferences and return it
- In the clearSharedPreferences function delete all values from preferences

Ex3 Create another activity named SecondActivity and in the XML file, add a text view:

Ex4 In the MainActivity java file create a new MySharedPreference.
- When the add button is clicked, take the text from the editText and save it in the SharedPreference using the save method.
- When the Go To Second Activity Button is clicked, make an intent and start the next activity(second activity)

Ex5 In the SecondActivity java class, Initialize the MySharedPreference and set the value of the textView with the String from the sharedPreference.
RUN THE APP
Ex6 Change the default colours of the application. Add Background to the items from the XML file.
Ex7 Send a primitive with the intent and show it in the second Activity (putExtra)