SharedPreferences in Android

As far as I know, SharedPreferences allow us to store some simple data in a named area in our phone. Introduction to the uses of SharedPreferences is very clear at Android SDK website. I just copied here(I divided the contents into four parts):

Introduction

The SharedPreferences class provides a general framework that allows you to save and retrieve persistent key-value pairs of primitive data types. 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).

Get SharedPreferences object

To get a SharedPreferences object for your application, use one of two methods:

• getSharedPreferences() - Use this if you need multiple preferences files identified by name, which you specify with the first parameter.
• getPreferences() - Use this if you need only one preferences file for your Activity. Because this will be the only preferences file for your Activity, you don't supply a name.

Write the values

To write values:

1. Call edit() to get a SharedPreferences.Editor.
2. Add values with methods such as putBoolean() and putString().
3. Commit the new values with commit()

Read the values

To read values, use SharedPreferences methods such as getBoolean() and getString().

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Now let's get into example time: 

First, take a look at AndroidManifest.xml file to get to know it.

<!--  part of AndroidManifest.xml  -->
<application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.sharedpreferences.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.example.sharedpreferences.Display"
            android:label="Display" >
        </activity>
    </application>

Two Activities exist in this example,

MainActivity.java which uses activity_main.xml as the content view; 

Display.java which uses main.xml as the content view:

//MainActivity.java
public class MainActivity extends Activity {
	private static final String MY_PREF="firstpreferencefile";
	private Button change;
	private EditText ed1;
	private EditText ed2;
	private SharedPreferences sp;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		change=(Button)findViewById(R.id.change);
		ed1=(EditText)findViewById(R.id.editText1);
		ed2=(EditText)findViewById(R.id.editText2);
		sp=getSharedPreferences(MY_PREF, 0);
		System.out.println("hello"+sp.getString("name", "null"));
				
		change.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				
				Editor editor=sp.edit();
				editor.putString("name", ed1.getText().toString());
				editor.putString("email", ed2.getText().toString());
				editor.commit();
				Intent intent=new Intent(getApplicationContext(),Display.class);
				startActivity(intent);
			}
		});
		
	}
}

//Display.java
public class Display extends Activity {
	private static final String MY_PREF="firstpreferencefile";
	private TextView tv1;
	private TextView tv2;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		SharedPreferences sp=getSharedPreferences(MY_PREF, 0);
		tv1=(TextView)findViewById(R.id.textView1);
		tv2=(TextView)findViewById(R.id.textView2);
		tv1.setText(sp.getString("name", "song"));
		tv2.setText(sp.getString("email", "jies.2408@gmail.com"));
	}
}

　　We set up two values and store them in SharedPreferences object. These two values can be changed in MainActivity.java, and would be displayed in main.java.