Android: How do I call a method of the main class from the preference activity class?

Question

I have the main activity class with a TextView and a settings activity (generated from the Android's Studio template).

On the settings activity, I've declared many settings. The TextView 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.

If I change something on the settings activity the listener will execute, but the value won't be updated on the main activity.

I can't use onResume() method because it's also executed the first time the app is launched.

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.

My main activity looks like:

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);
}

}

And this is the settings activity (look the function called onSharedPreferenceChanged ):

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) && !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
            & Configuration.SCREENLAYOUT_SIZE_MASK) >= 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 < Build.VERSION_CODES.HONEYCOMB
            || !isXLargeTablet(context);
}

/**
 * {@inheritDoc}
 */
@Override
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public void onBuildHeaders(List<Header> 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 >= 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"));
    }
}

}

Bonus question: I've generated the settings activity using the Android's Studio template, I've noticed that there's no onCreate() method, is this normal? What does executed when I call the startactivity() function from the main activity?

Thank you.

PS: Maybe I've posted too many code to solve the question, sorry I just started with Android and feel like a noob.

Answer 1

You should not trying to change the UI of MainActivity from SettingsActivity ! The management of the MainActivity 's UI should only be done by itself.

Take a look at the Activity Lifecycle . You will see that the onResume() method of the MainActivity will be called when the Activity will come back on the foreground. So two solutions :

1. You call loadPrefs() in the onResume() . You tell you can't do it, but I don't understand why (maybe I miss some details)
2. In the onResume() method, call loadPrefs() only if changes are detected.

Again : do not try to call a method of MainActivity from another class : it's a non-sense in Android world.

Bonus anwser

The onCreate() method is declared in the Activity class and so has a default behavior. If you want to modify the default behavior (ie declaring your own UI components), you can override it (doing so when adding @Override annotation). So by default, there is no absolut need to override it. And if not override the default implementation will be called. It's an OOP basis ;)

Answer 2

1. No need to start main activity from settings activity
2. Call loadPrefs() from main activity's onResume() rather than from onCreate()
3. There is onCreate() method in settings activity.