android - sharedpreferences return null value

Question

I'm trying to use sharedpreferences to check whether the user logged in before they start using the app. I save the username in shredpreferences when user log in.

Login.java

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);     
        Button btnLogin = (Button) findViewById(R.id.buttonlogin);      
        btnLogin.setOnClickListener(new View.OnClickListener() {
            public void onClick(View adapt) {
                EditText usernameEditText = (EditText) findViewById(R.id.EditUserName);
                userName = usernameEditText.getText().toString();
                EditText passwordEditText = (EditText) findViewById(R.id.EditPassword);
                userPassword = passwordEditText.getText().toString();               
                if (userName.matches("") && userPassword.matches("")) {
                    toast("Please enter Username and Password");
                    return;
                } else if (userName.matches("") || userName.equals("")) {
                    toast("Please enter Username");
                    return;
                } else if (userPassword.matches("") || userPassword.equals("")) {
                    toast("Please enter Password");
                    return;
                } else {
                    SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
                    SharedPreferences.Editor editor = sharedPreferences.edit();
                    editor.putString("MEM1", userName);
                    editor.commit();
                    new DownloadFilesTask().execute();
                }           
            }
        });
    }

    private void toast(String text) {
        Toast.makeText(this, text, Toast.LENGTH_SHORT).show();
    }

    private class DownloadFilesTask extends AsyncTask<Void, Void, Void> {
        protected void onPreExecute() {
        }

        protected void onPostExecute(Void result) {
            toast("user logged in");
            startActivity(new Intent(Login.this, MainActivity.class));
            finish();
        }

        @Override
        protected Void doInBackground(Void... params) {         
            return null;
        }
    }

}

and I tried to check the username value before I start my mainactivity.

SharedPreferences sharedPreferences = getPreferences(MODE_PRIVATE);
    String username =sharedPreferences.getString("MEM1", "");
    if(username.equalsIgnoreCase("")||username.length()==0)
    {
        toast("username is null");
        startActivity(new Intent(MainActivity.this, Login.class));
        finish();
    }

but the username is always null. Please help. Thanks

Answer 1

Calling getPreferences means that you have to be in the same activity. Using getSharedPreferences allows you to share the preferences between activities. You just have to define a name for the preferences when calling getSharedPreferences("Pref name here", MODE_PRIVATE);