My Android alert appears twice after logging in

Question

I'm testing out a notification that tells the user of an Android app whether or not there is an internet connection. I have inserted the code that does this into the onResume function, as seen below:

@Override
protected void onResume(){
    super.onResume();
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setPositiveButton(R.string.OK, new DialogInterface.OnClickListener() {
           public void onClick(DialogInterface dialog, int id) {
               dialog.dismiss();
           }
       });
    if(isNetworkConnected()){
        builder.setMessage(R.string.yes_internet)
           .setTitle(R.string.title);
    }
    else{
        builder.setMessage(R.string.no_internet)
           .setTitle(R.string.title);
    }
    AlertDialog dialog = builder.create();
    dialog.show();
}

private boolean isNetworkConnected() {
      ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
      NetworkInfo ni = cm.getActiveNetworkInfo();
      if (ni == null) {
          // There are no active networks.
          return false;
      }
      else{
          return true;
      }
}

Which works just fine. Except for the part where after you log in, see the alert, and dismiss it, another identical alert appears. This only happens after logging in, it does not happen if you leave the app and then come back to it. My login activity (which is the one automatically generated by Eclipse) is called from onCreate, so that it will only run when the app is launched. So, it would appear that something about the login activity is causing onResume to be called twice. But I have no idea what that could be.

Here is the code for the login activity:

/**
 * Activity which displays a login screen to the user, offering registration as
 * well.
 */
public class LoginActivity extends Activity {
/**
 * 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[] {
        "foo@example.com:hello", "bar@example.com:world" };

/**
 * The default email to populate the email field with.
 */
public static final String EXTRA_EMAIL = "com.example.android.authenticatordemo.extra.EMAIL";

/**
 * Keep track of the login task to ensure we can cancel it if requested.
 */
private UserLoginTask mAuthTask = null;

// Values for email and password at the time of the login attempt.
private String mEmail;
private String mPassword;

// UI references.
private EditText mEmailView;
private EditText mPasswordView;
private View mLoginFormView;
private View mLoginStatusView;
private TextView mLoginStatusMessageView;

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

    setContentView(R.layout.activity_login);

    // Set up the login form.
    mEmail = getIntent().getStringExtra(EXTRA_EMAIL);
    mEmailView = (EditText) findViewById(R.id.email);
    mEmailView.setText(mEmail);

    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;
                }
            });

    mLoginFormView = findViewById(R.id.login_form);
    mLoginStatusView = findViewById(R.id.login_status);
    mLoginStatusMessageView = (TextView) findViewById(R.id.login_status_message);

    findViewById(R.id.sign_in_button).setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    attemptLogin();
                }
            });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);
    getMenuInflater().inflate(R.menu.login, menu);
    return true;
}

/**
 * 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.
 */
public void attemptLogin() {
    if (mAuthTask != null) {
        return;
    }

    // Reset errors.
    mEmailView.setError(null);
    mPasswordView.setError(null);

    // Store values at the time of the login attempt.
    mEmail = mEmailView.getText().toString();
    mPassword = mPasswordView.getText().toString();

    boolean cancel = false;
    View focusView = null;

    // Check for a valid password.
    if (TextUtils.isEmpty(mPassword)) {
        mPasswordView.setError(getString(R.string.error_field_required));
        focusView = mPasswordView;
        cancel = true;
    } else if (mPassword.length() < 4) {
        mPasswordView.setError(getString(R.string.error_invalid_password));
        focusView = mPasswordView;
        cancel = true;
    }

    // Check for a valid email address.
    if (TextUtils.isEmpty(mEmail)) {
        mEmailView.setError(getString(R.string.error_field_required));
        focusView = mEmailView;
        cancel = true;
    } else if (!mEmail.contains("@")) {
        mEmailView.setError(getString(R.string.error_invalid_email));
        focusView = mEmailView;
        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.
        mLoginStatusMessageView.setText(R.string.login_progress_signing_in);
        showProgress(true);
        mAuthTask = new UserLoginTask();
        mAuthTask.execute((Void) null);
    }
}

/**
 * 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);

        mLoginStatusView.setVisibility(View.VISIBLE);
        mLoginStatusView.animate().setDuration(shortAnimTime)
                .alpha(show ? 1 : 0)
                .setListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        mLoginStatusView.setVisibility(show ? View.VISIBLE
                                : View.GONE);
                    }
                });

        mLoginFormView.setVisibility(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);
                    }
                });
    } else {
        // The ViewPropertyAnimator APIs are not available, so simply show
        // and hide the relevant UI components.
        mLoginStatusView.setVisibility(show ? View.VISIBLE : View.GONE);
        mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
    }
}

/**
 * Represents an asynchronous login/registration task used to authenticate
 * the user.
 */
public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
    @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;
        }

        for (String credential : DUMMY_CREDENTIALS) {
            String[] pieces = credential.split(":");
            if (pieces[0].equals(mEmail)) {
                // Account exists, return true if the password matches.
                return pieces[1].equals(mPassword);
            }
        }

        // TODO: register the new account here.
        return true;
    }

    @Override
    protected void onPostExecute(final Boolean success) {
        mAuthTask = null;
        showProgress(false);

        if (success) {
            finish();
        } else {
            mPasswordView
                    .setError(getString(R.string.error_incorrect_password));
            mPasswordView.requestFocus();
        }
    }

    @Override
    protected void onCancelled() {
        mAuthTask = null;
        showProgress(false);
    }
}

Answer 1

I think this is possible scenario where your MainActivity's onResume is called twice, I assume that you start LoginActivity in MainActivity's onCreate:

1. MainActivity is created and LoginActivity is launched. MainActivity still continues its lifecycle - onResume is called (and onPause right after etc..)...
2. When you finish your LoginActivity, then MainActivity is resumed again - onResume is called for the second time.

You can consider saving some boolean value (or the whole dialog) to preserve showing the dialog for the second time, or you can change your workflow so that MainActivity is started AFTER successful login.

Answer 2

It's not possible to detect the error from the code that you posted so far. You should make sure you study the following picture a little bit and refactor your code with it in mind.

Make sure that calls to other activities/methods do not pause/resume your main activity multiple times! That would only cause onResume() to be called several times.

From http://developer.android.com/training/basics/activity-lifecycle/starting.html