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:
- Call
edit()to get aSharedPreferences.Editor. - Add values with methods such as
putBoolean()andputString(). - Commit the new values with
commit()
Read the values
To read values, use SharedPreferences methods
such as getBoolean() and getString().
_______________________________________________________________________________________________________________________
Now let‘s get into example time:
First, take a look at AndroidManifest.xml file to get to know it.
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<!-- 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>
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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:
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<span style="color: rgb(153, 204, 0);"><strong>//MainActivity.java</strong></span><br>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);
}
});
}
} |
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<span style="color: rgb(153, 204, 0);"><strong>//Display.java</strong></span>
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.