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SharedPreferences in Android

2024-07-07 03:41:35   219人阅读

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.

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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>

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.

 


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