注销时如何破坏活动？

Question

I am developing apps in android. In that I have login and logout activity with session management using SharedPreferences. my apps logout , store data in sharedpreferences to maintain session successfully done. when I do logout from the apps(second activity) and get rendered to first activity(login activity ) but what happen is when i clicked back button on emulator after successfully logout still again rendered to second activity and some version like 2.3.3 etc encountered exception

java.lang.RuntimeException: Unable to destroy activity {com.oj.bs/com.oj.bs.LoginActivity}: java.lang.NullPointerException

can anybody fix the problem. please refer following code

following is the login activity code

sessionmngr = new SessionManager(getApplicationContext());

                    JSONObject json_user = jsonObj.getJSONObject("user");
                    sessionmngr.createLoginSession(id,json_user.getString(KEY_UNAME), 
                            json_user.getString(KEY_UEMAIL));
                     .
                     .

following is the Session Management

public class SessionManager {

SharedPreferences pref;
Editor editor;
Context contxt;
//shared pref mode
int PRIVATE_MODE = 0;
 // Sharedpref file name
private static final String PREF_NAME = "bookingScapePref";

// All Shared Preferences Keys
private static final String IS_LOGIN = "IsLoggedIn";
public static final String KEY_NAME = "name";
public static final String KEY_ID = "id";
public static final String KEY_EMAIL = "email";

public SessionManager(Context context) {
    super();
    this.contxt = context;
    pref = context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
    editor = pref.edit();
    editor.commit();
}
/**
 * Create login session
 * */
public void createLoginSession(int id,String name, String email) {

    editor.putBoolean(IS_LOGIN,true);
    editor.putString(KEY_NAME, name);
    editor.putString(KEY_EMAIL, email);
    editor.putInt(KEY_ID, id);
    editor.commit();
}
/**
 * Get stored session data
 * */
public HashMap<String, String> getUserDetails() {
    HashMap<String, String> userDetails = new HashMap<String, String>();
    userDetails.put(KEY_NAME, pref.getString(KEY_NAME, null));
    userDetails.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));
    return userDetails;
}
/**
 * Check login method will check user login status
 * */
public void checkLogin() {

    if (!this.isLoggedIn()) {
        Intent i = new Intent(contxt, LoginActivity.class);
        //closing all the activity
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        //Add new Flag to start new Activity
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

        contxt.startActivity(i);
    }
}

public void logoutUser() {
    //clearing all data from sharedPreferences
    editor.clear();
    editor.commit();
    Intent intnt = new Intent(contxt, LoginActivity.class);
    // Closing all the Activities
    intnt.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

    // Add new Flag to start new Activity
    intnt.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

    // Staring Login Activity
    contxt.startActivity(intnt);
}

/**
 * Quick check for login
 * **/
// Get Login State
public boolean isLoggedIn(){
    return pref.getBoolean(IS_LOGIN, false);
}

}

this is second activity here i'm checking session

public class ProjectFragActivity extends SherlockFragmentActivity {

SessionManager sessionMngr ;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    sessionMngr = new SessionManager(getApplicationContext());

    Toast.makeText(getApplicationContext(), "User Login Status: " + sessionMngr .isLoggedIn(), 
            Toast.LENGTH_LONG).show();
    sessionMngr.checkLogin();
            .
            .

Answer 1

@Override
public void onBackPressed() {
// TODO Auto-generated method stub
    Intent intent = new Intent(Intent.ACTION_MAIN);
    intent.addCategory(Intent.CATEGORY_HOME);
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivity(intent);
super.onBackPressed();
}

Hi, Use onBackpressed function in your login Screen and implement this Intent function. It will take you to the home screen of the phone.

Hope this will give you some solution.

Answer 2

A simpler solution should be to call finish(); in your second activity.

Answer 3

First don't call finish() in destroy() , the activity is already finishing and going away, plus that screws up with everything else. What you need to do is call finish() upon logging out, whatever function you have to log the person out, at the end of it, put finish() .