title: Android: How do I call a method of the main class from the preference activity class?
body: <p>I have the main activity class with a <code>TextView</code> and a settings activity (generated from the Android's Studio template).</p>
  
  <p>On the settings activity, I've declared many settings. The <code>TextView</code> on the main activity shows one of this settings, this is made by a function that loads the current state of all preferences and saves them on variables.</p>
  
  <p>If I change something on the settings activity the listener will execute, but the value won't be updated on the main activity.</p>
  
  <p>I can't use <code>onResume()</code> method because it's also executed the first time the app is launched.</p>
  
  <p>I've tried sending an Intent and starting the main class from the listener, but that creates a new instance of the main class, and only allows you to change just one preference because the listener triggers. </p>
  
  <p>My main activity looks like:</p>
  
  <pre><code>public class MainActivity extends ActionBarActivity {
  
  private SharedPreferences prefs;
  
  private double _lat;
  
  
  public void loadPrefs(){
  
      prefs = PreferenceManager.getDefaultSharedPreferences(this);
      _lat = Double.parseDouble(prefs.getString("lat", ""));
  
      //updates the iu
      TextView helloThere = (TextView) findViewById(R.id.TextView_hello_world);
      helloThere.setText(Double.toString(_lat));
  }
  
  @Override
  protected void onResume() {
      super.onResume();
      String changes = getIntent().getStringExtra("prefChanged");
      if(changes != null)
          Log.d("DEBUG!!!!", changes);
      else
          Log.d("DEBUG!!!!", "No changes!!!!");
  }
  
  
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
  
      loadPrefs();
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
  
      if (id == R.id.action_settings) {
          // Launch Settings activity
          Intent intent = new Intent(this, SettingsActivity.class);
          startActivity(intent);
          return true;
      }
      return super.onOptionsItemSelected(item);
  }
  </code></pre>
  
  <p>}</p>
  
  <p>And this is the settings activity (look the function called <code>onSharedPreferenceChanged</code>):</p>
  
  <pre><code>public class SettingsActivity extends PreferenceActivity implements SharedPreferences.OnSharedPreferenceChangeListener {
  SharedPreferences.OnSharedPreferenceChangeListener listener;
  /**
   * Determines whether to always show the simplified settings UI, where
   * settings are presented in a single list. When false, settings are shown
   * as a master/detail two-pane view on tablets. When true, a single pane is
   * shown on tablets.
   */
  private static final boolean ALWAYS_SIMPLE_PREFS = false;
  private SharedPreferences prefs;
  
  @Override
  public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
      Log.d("DEBUG!!","LISTENER!!");
      Intent i = new Intent(this, MainActivity.class);
      i.putExtra("prefChanged","Something changed...");
      startActivity(i);
  }
  
  @Override
  protected void onResume() {
      super.onResume();
      prefs.registerOnSharedPreferenceChangeListener(this);
  }
  
  @Override
  protected void onPause() {
      super.onPause();
      prefs.unregisterOnSharedPreferenceChangeListener(this);
  }
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      prefs = PreferenceManager.getDefaultSharedPreferences(this);
  }
  
  @Override
  protected void onPostCreate(Bundle savedInstanceState) {
      super.onPostCreate(savedInstanceState);
  
      setupSimplePreferencesScreen();
  }
  
  /**
   * Shows the simplified settings UI if the device configuration if the
   * device configuration dictates that a simplified, single-pane UI should be
   * shown.
   */
  private void setupSimplePreferencesScreen() {
      if (!isSimplePreferences(this)) {
          return;
      }
  
      // In the simplified UI, fragments are not used at all and we instead
      // use the older PreferenceActivity APIs.
  
      // Add 'general' preferences.
      addPreferencesFromResource(R.xml.pref_general);
  
      // Add 'notifications' preferences, and a corresponding header.
      PreferenceCategory fakeHeader = new PreferenceCategory(this);
      fakeHeader.setTitle(R.string.pref_header_notifications);
      getPreferenceScreen().addPreference(fakeHeader);
      addPreferencesFromResource(R.xml.pref_notification);
  
      // Add 'data and sync' preferences, and a corresponding header.
      //fakeHeader = new PreferenceCategory(this);
      //fakeHeader.setTitle(R.string.pref_header_data_sync);
      //getPreferenceScreen().addPreference(fakeHeader);
      //addPreferencesFromResource(R.xml.pref_data_sync);
  
      // Bind the summaries of EditText/List/Dialog/Ringtone preferences to
      // their values. When their values change, their summaries are updated
      // to reflect the new value, per the Android Design guidelines.
      //bindPreferenceSummaryToValue(findPreference("example_text"));
      //bindPreferenceSummaryToValue(findPreference("example_list"));
      bindPreferenceSummaryToValue(findPreference("notifications_ringtone"));
      //bindPreferenceSummaryToValue(findPreference("sync_frequency"));
  }
  
  /**
   * {@inheritDoc}
   */
  @Override
  public boolean onIsMultiPane() {
      return isXLargeTablet(this) &amp;&amp; !isSimplePreferences(this);
  }
  
  /**
   * Helper method to determine if the device has an extra-large screen. For
   * example, 10" tablets are extra-large.
   */
  private static boolean isXLargeTablet(Context context) {
      return (context.getResources().getConfiguration().screenLayout
              &amp; Configuration.SCREENLAYOUT_SIZE_MASK) &gt;= Configuration.SCREENLAYOUT_SIZE_XLARGE;
  }
  
  /**
   * Determines whether the simplified settings UI should be shown. This is
   * true if this is forced via {@link #ALWAYS_SIMPLE_PREFS}, or the device
   * doesn't have newer APIs like {@link PreferenceFragment}, or the device
   * doesn't have an extra-large screen. In these cases, a single-pane
   * "simplified" settings UI should be shown.
   */
  private static boolean isSimplePreferences(Context context) {
      return ALWAYS_SIMPLE_PREFS
              || Build.VERSION.SDK_INT &lt; Build.VERSION_CODES.HONEYCOMB
              || !isXLargeTablet(context);
  }
  
  /**
   * {@inheritDoc}
   */
  @Override
  @TargetApi(Build.VERSION_CODES.HONEYCOMB)
  public void onBuildHeaders(List&lt;Header&gt; target) {
      if (!isSimplePreferences(this)) {
          loadHeadersFromResource(R.xml.pref_headers, target);
      }
  }
  
  /**
   * A preference value change listener that updates the preference's summary
   * to reflect its new value.
   */
  private static Preference.OnPreferenceChangeListener sBindPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() {
      @Override
      public boolean onPreferenceChange(Preference preference, Object value) {
          String stringValue = value.toString();
  
          if (preference instanceof ListPreference) {
              // For list preferences, look up the correct display value in
              // the preference's 'entries' list.
              ListPreference listPreference = (ListPreference) preference;
              int index = listPreference.findIndexOfValue(stringValue);
  
              // Set the summary to reflect the new value.
              preference.setSummary(
                      index &gt;= 0
                              ? listPreference.getEntries()[index]
                              : null);
  
          } else if (preference instanceof RingtonePreference) {
              // For ringtone preferences, look up the correct display value
              // using RingtoneManager.
              if (TextUtils.isEmpty(stringValue)) {
                  // Empty values correspond to 'silent' (no ringtone).
                  preference.setSummary(R.string.pref_ringtone_silent);
  
              } else {
                  Ringtone ringtone = RingtoneManager.getRingtone(
                          preference.getContext(), Uri.parse(stringValue));
  
                  if (ringtone == null) {
                      // Clear the summary if there was a lookup error.
                      preference.setSummary(null);
                  } else {
                      // Set the summary to reflect the new ringtone display
                      // name.
                      String name = ringtone.getTitle(preference.getContext());
                      preference.setSummary(name);
                  }
              }
  
          } else {
              // For all other preferences, set the summary to the value's
              // simple string representation.
              preference.setSummary(stringValue);
          }
          return true;
      }
  };
  
  /**
   * Binds a preference's summary to its value. More specifically, when the
   * preference's value is changed, its summary (line of text below the
   * preference title) is updated to reflect the value. The summary is also
   * immediately updated upon calling this method. The exact display format is
   * dependent on the type of preference.
   *
   * @see #sBindPreferenceSummaryToValueListener
   */
  private static void bindPreferenceSummaryToValue(Preference preference) {
      // Set the listener to watch for value changes.
      preference.setOnPreferenceChangeListener(sBindPreferenceSummaryToValueListener);
  
      // Trigger the listener immediately with the preference's
      // current value.
      sBindPreferenceSummaryToValueListener.onPreferenceChange(preference,
              PreferenceManager
                      .getDefaultSharedPreferences(preference.getContext())
                      .getString(preference.getKey(), ""));
  }
  
  
  /**
   * This fragment shows general preferences only. It is used when the
   * activity is showing a two-pane settings UI.
   */
  @TargetApi(Build.VERSION_CODES.HONEYCOMB)
  public static class GeneralPreferenceFragment extends PreferenceFragment {
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          addPreferencesFromResource(R.xml.pref_general);
  
          // Bind the summaries of EditText/List/Dialog/Ringtone preferences
          // to their values. When their values change, their summaries are
          // updated to reflect the new value, per the Android Design
          // guidelines.
          //bindPreferenceSummaryToValue(findPreference("fixed_lat_long"));
          bindPreferenceSummaryToValue(findPreference("example_text"));
          bindPreferenceSummaryToValue(findPreference("example_list"));
      }
  }
  
  /**
   * This fragment shows notification preferences only. It is used when the
   * activity is showing a two-pane settings UI.
   */
  @TargetApi(Build.VERSION_CODES.HONEYCOMB)
  public static class NotificationPreferenceFragment extends PreferenceFragment {
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          addPreferencesFromResource(R.xml.pref_notification);
  
          // Bind the summaries of EditText/List/Dialog/Ringtone preferences
          // to their values. When their values change, their summaries are
          // updated to reflect the new value, per the Android Design
          // guidelines.
              bindPreferenceSummaryToValue(findPreference("notifications_ringtone"));
      }
  }
  </code></pre>
  
  <p>}</p>
  
  <p>Bonus question: I've generated the settings activity using the Android's Studio template, I've noticed that there's no <code>onCreate()</code> method, is this normal? What does executed when I call the <code>startactivity()</code> function from the main activity?</p>
  
  <p>Thank you.</p>
  
  <p>PS: Maybe I've posted too many code to solve the question, sorry I just started with Android and feel like a noob.</p>