Logout clear SharedPreferences

问题:

I have a login page that saves username and password to SharedPreferences. I have another Activity class that includes a logout button. I want to clear SharedPreferences when I click the logout button. The problem is that I don't get the SharedPreferences from this class. How can I get the SharedPreferences?

LoginPage

public class MainActivity extends Activity {
public SharedPreferences.Editor loginPrefsEditor;
    public  SharedPreferences loginPreferences;
    private Boolean saveLogin;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    name = (EditText) findViewById(R.id.et_Username);
        pass = (EditText) findViewById(R.id.et_Password);
        login = (Button) findViewById(R.id.bt_Login);

         loginPreferences = getSharedPreferences("loginPrefs", MODE_PRIVATE);
         loginPrefsEditor = loginPreferences.edit();

         saveLogin = loginPreferences.getBoolean("saveLogin", false);

         if (saveLogin == true) {
                name.setText(loginPreferences.getString("username", ""));
                pass.setText(loginPreferences.getString("password", ""));   
            }

        login.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View v) {
                 name1 = name.getText().toString();
                 pass1 = pass.getText().toString();
               //new Thread (new Task()).start();
                    loginPrefsEditor.putBoolean("saveLogin", true);
                    loginPrefsEditor.putString("username", name1);
                    loginPrefsEditor.putString("password", pass1);
                    loginPrefsEditor.commit();
                 new myAsyncTask().execute();
            }
        });
}

Logout Button in AnotherActivity

 logout.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                // Launching News Feed Screen

                Intent i = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(i);
            }
        });

回答1:

Try this !

logout.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            // Launching News Feed Screen

             SharedPreferences preferences =getSharedPreferences("loginPrefs",Context.MODE_PRIVATE);
             SharedPreferences.Editor editor = preferences.edit();
             editor.clear();
             editor.apply();
             finish();
 });

回答2:

I think you have a trouble in understanding Shared preferences in android .

According to official documentation

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.

You should have a Context for using both the above methods .

Also Shared preferences are stored asa key value pair , so clearing should mean that you set the values to some empty string.

For more details , and better explanation you can read here http://developer.android.com/guide/topics/data/data-storage.html#pref and http://www.vogella.com/tutorials/AndroidFileBasedPersistence/article.html

Hope this will help.

Cheers!

回答3:

It as Simple. Like you save your data in SharedPrefernce

SharedPreferences sp = getSharedPreferences("MYKEY",0);
SharedPreferences.Editor editor = sp.edit();
editor.putString("username" , username);
editor.putString("password" , password);

Now you can retrieve as in any class of your app like,

SharedPreferences sp = getSharedPreferences("MYKEY",0);
String uname = sp.getString("username");
String pwd = sp.getString("password");

And for clear your username and password

editor.clear();
editor.commit();

or

editor.remove("username");
editor.remove("password");
editor.commit();

回答4:

Why not write a SharedPreference utility class. This can be accessed from both the activities.

回答5:

SharedPreferences mPrefs = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = mPrefs.edit();
editor.clear();
editor.commit();