gt:         protected void onPostExecute(final Boolean success) {
context: package edu.upc.eetac.dsa.kujosa;
  
  import android.animation.Animator;
  import android.animation.AnimatorListenerAdapter;
  import android.annotation.TargetApi;
  import android.app.LoaderManager.LoaderCallbacks;
  import android.content.CursorLoader;
  import android.content.Intent;
  import android.content.Loader;
  import android.content.pm.PackageManager;
  import android.database.Cursor;
  import android.net.Uri;
  import android.os.AsyncTask;
  import android.os.Build;
  import android.os.Bundle;
  import android.provider.ContactsContract;
  import android.support.annotation.NonNull;
  import android.support.design.widget.Snackbar;
  import android.support.v7.app.AppCompatActivity;
  import android.text.TextUtils;
  import android.view.KeyEvent;
  import android.view.View;
  import android.view.View.OnClickListener;
  import android.view.inputmethod.EditorInfo;
  import android.widget.ArrayAdapter;
  import android.widget.AutoCompleteTextView;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.TextView;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import edu.upc.eetac.dsa.kujosa.client.KujosaClient;
  
  import static android.Manifest.permission.READ_CONTACTS;
  
  /**
   * A login screen that offers login via email/password.
   */
  public class LoginActivity extends AppCompatActivity implements LoaderCallbacks<Cursor> {
  
      /**
       * Id to identity READ_CONTACTS permission request.
       */
      private static final int REQUEST_READ_CONTACTS = 0;
  
      /**
       * A dummy authentication store containing known user names and passwords.
       * TODO: remove after connecting to a real authentication system.
       */
      private static final String[] DUMMY_CREDENTIALS = new String[]{
              "alicia:alicia", "blas:blas"
      };
      /**
       * Keep track of the login task to ensure we can cancel it if requested.
       */
      private UserLoginTask mAuthTask = null;
  
      // UI references.
      private AutoCompleteTextView mLoginidView;
      private EditText mPasswordView;
      private View mProgressView;
      private View mLoginFormView;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_login);
          Intent intent = getIntent();
          // Set up the login form.
          mLoginidView = (AutoCompleteTextView) findViewById(R.id.username);
          populateAutoComplete();
  
          mPasswordView = (EditText) findViewById(R.id.password);
          mPasswordView.setOnEditorActionListener(new TextView.OnEditorActionListener() {
              @Override
              public boolean onEditorAction(TextView textView, int id, KeyEvent keyEvent) {
                  if (id == R.id.login || id == EditorInfo.IME_NULL) {
                      attemptLogin();
                      return true;
                  }
                  return false;
              }
          });
  
          Button mEmailSignInButton = (Button) findViewById(R.id.email_sign_in_button);
          mEmailSignInButton.setOnClickListener(new OnClickListener() {
              @Override
              public void onClick(View view) {
                  attemptLogin();
              }
          });
  
          mLoginFormView = findViewById(R.id.login_form);
          mProgressView = findViewById(R.id.login_progress);
      }
  
      private void populateAutoComplete() {
          if (!mayRequestContacts()) {
              return;
          }
  
          getLoaderManager().initLoader(0, null, this);
      }
  
      private boolean mayRequestContacts() {
          if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
              return true;
          }
          if (checkSelfPermission(READ_CONTACTS) == PackageManager.PERMISSION_GRANTED) {
              return true;
          }
          if (shouldShowRequestPermissionRationale(READ_CONTACTS)) {
              Snackbar.make(mLoginidView, R.string.permission_rationale, Snackbar.LENGTH_INDEFINITE)
                      .setAction(android.R.string.ok, new OnClickListener() {
                          @Override
                          @TargetApi(Build.VERSION_CODES.M)
                          public void onClick(View v) {
                              requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS);
                          }
                      });
          } else {
              requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS);
          }
          return false;
      }
  
      /**
       * Callback received when a permissions request has been completed.
       */
      @Override
      public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
                                             @NonNull int[] grantResults) {
          if (requestCode == REQUEST_READ_CONTACTS) {
              if (grantResults.length == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                  populateAutoComplete();
              }
          }
      }
  
  
      /**
       * Attempts to sign in or register the account specified by the login form.
       * If there are form errors (invalid email, missing fields, etc.), the
       * errors are presented and no actual login attempt is made.
       */
      private void attemptLogin() {
          if (mAuthTask != null) {
              return;
          }
  
          // Reset errors.
          mLoginidView.setError(null);
          mPasswordView.setError(null);
  
          // Store values at the time of the login attempt.
          String email = mLoginidView.getText().toString();
          String password = mPasswordView.getText().toString();
  
          boolean cancel = false;
          View focusView = null;
  
          // Check for a valid password, if the user entered one.
          if (!TextUtils.isEmpty(password) && !isPasswordValid(password)) {
              mPasswordView.setError(getString(R.string.error_invalid_password));
              focusView = mPasswordView;
              cancel = true;
          }
  
          // Check for a valid email address.
          if (TextUtils.isEmpty(email)) {
              mLoginidView.setError(getString(R.string.error_field_required));
              focusView = mLoginidView;
              cancel = true;
          } else if (!isEmailValid(email)) {
              mLoginidView.setError(getString(R.string.error_invalid_email));
              focusView = mLoginidView;
              cancel = true;
          }
  
          if (cancel) {
              // There was an error; don't attempt login and focus the first
              // form field with an error.
              focusView.requestFocus();
          } else {
              // Show a progress spinner, and kick off a background task to
              // perform the user login attempt.
              showProgress(true);
              mAuthTask = new UserLoginTask(email, password);
              mAuthTask.execute((Void) null);
          }
      }
      private boolean isEmailValid(String email) {
          //TODO: Replace this with your own logic
          //return email.contains("@");
          return true;
      }
  
      private boolean isPasswordValid(String password) {
          //TODO: Replace this with your own logic
          return password.length() > 4;
      }
  
      /**
       * Shows the progress UI and hides the login form.
       */
      @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
      private void showProgress(final boolean show) {
          // On Honeycomb MR2 we have the ViewPropertyAnimator APIs, which allow
          // for very easy animations. If available, use these APIs to fade-in
          // the progress spinner.
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
              int shortAnimTime = getResources().getInteger(android.R.integer.config_shortAnimTime);
  
              mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
              mLoginFormView.animate().setDuration(shortAnimTime).alpha(
                      show ? 0 : 1).setListener(new AnimatorListenerAdapter() {
                  @Override
                  public void onAnimationEnd(Animator animation) {
                      mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
                  }
              });
  
              mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
              mProgressView.animate().setDuration(shortAnimTime).alpha(
                      show ? 1 : 0).setListener(new AnimatorListenerAdapter() {
                  @Override
                  public void onAnimationEnd(Animator animation) {
                      mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
                  }
              });
          } else {
              // The ViewPropertyAnimator APIs are not available, so simply show
              // and hide the relevant UI components.
              mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
              mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
          }
      }
  
  
      @Override
      public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
          return new CursorLoader(this,
                  // Retrieve data rows for the device user's 'profile' contact.
                  Uri.withAppendedPath(ContactsContract.Profile.CONTENT_URI,
                          ContactsContract.Contacts.Data.CONTENT_DIRECTORY), ProfileQuery.PROJECTION,
  
                  // Select only email addresses.
                  ContactsContract.Contacts.Data.MIMETYPE +
                          " = ?", new String[]{ContactsContract.CommonDataKinds.Email
                                                                       .CONTENT_ITEM_TYPE},
  
                  // Show primary email addresses first. Note that there won't be
                  // a primary email address if the user hasn't specified one.
                  ContactsContract.Contacts.Data.IS_PRIMARY + " DESC");
      }
  
      @Override
      public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
          List<String> emails = new ArrayList<>();
          cursor.moveToFirst();
          while (!cursor.isAfterLast()) {
              emails.add(cursor.getString(ProfileQuery.ADDRESS));
              cursor.moveToNext();
          }
  
          addEmailsToAutoComplete(emails);
      }
  
      @Override
      public void onLoaderReset(Loader<Cursor> cursorLoader) {
  
      }
  
      private interface ProfileQuery {
          String[] PROJECTION = {
                  ContactsContract.CommonDataKinds.Email.ADDRESS,
                  ContactsContract.CommonDataKinds.Email.IS_PRIMARY,
          };
  
          int ADDRESS = 0;
          int IS_PRIMARY = 1;
      }
  
  
      private void addEmailsToAutoComplete(List<String> emailAddressCollection) {
          //Create adapter to tell the AutoCompleteTextView what to show in its dropdown list.
          ArrayAdapter<String> adapter =
                  new ArrayAdapter<>(LoginActivity.this,
                          android.R.layout.simple_dropdown_item_1line, emailAddressCollection);
  
          mLoginidView.setAdapter(adapter);
      }
  
      /**
       * Represents an asynchronous login/registration task used to authenticate
       * the user.
       */
      public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
  
          private final String mLoginid;
          private final String mPassword;
  
          UserLoginTask(String loginid, String password) {
              mLoginid = loginid;
              mPassword = password;
          }
  
          @Override
          protected Boolean doInBackground(Void... params) {
              // TODO: attempt authentication against a network service.
  
              try {
                  // Simulate network access.
                  Thread.sleep(2000);
              } catch (InterruptedException e) {
                  return false;
              }
  
              String[] pieces = new String[0];
              for (String credential : DUMMY_CREDENTIALS) {
                  pieces = credential.split(":");
                  if (pieces[0].equals(mLoginid)) {
                      // Account exists, return true if the password matches.
                      return pieces[1].equals(mPassword);
                  }
              }
              KujosaClient client = KujosaClient.getInstance();
              boolean result = client.login(pieces[0], pieces[1]);
  
              // TODO: register the new account here.
              return result;
          }
  
          @Override
  