Question

I have an IntentService which updates a preference like this:

SharedPreferences.Editor editor = userPrefs.edit();
editor.putInt("COUNT", intCount);
editor.commit();

In my main activity I am listening for preference changes and update a TextView

userPrefsListener = new SharedPreferences.OnSharedPreferenceChangeListener() {

@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {

  if(key.equals("COUNT")) {

    final TextView txvCounter = (TextView) findViewById(R.id.TXV_COUNTER);

    if(txvCounter != null) {

    SharedPreferences userPrefs = getSharedPreferences("USER_SCORE", 0);
    int intCount = userPrefs.getInt("COUNT", 0);
    txvFishcounter.setText(String.format("%03d",intCount));
    }
  }
}
};

userPrefs.registerOnSharedPreferenceChangeListener(userPrefsListener);

For Android 2.3 everything works fine, but for 2.2 I’m getting CalledFromWrongThreadException everytime the OnSharedListener is triggered.

Thanks for your Help!

Answer 1

The reason why the CalledFromWrongThreadException is raised, is because the OnChangeListener is not supposed to be called from the IntentService.

What you could do though, is sending a Broadcast (where you can actually include the value as well).

In case you are only using the SharedPreference for communication, you can replace it entirely (and I would recommend this, as SharedPreferences are wasting Write Cycles).

You could use a code like this for sending a Broadcast:

/**
 * Send an Intent with the Broadcast, a permission and a Bundle
 * 
 * @param context
 *            A context to use
 * @param broadcast
 *            String to use, eg. "de.bulling.smstalk.ENABLE"
 * @param permission
 *            Permission needed for receiving
 * @param bundle
 *            Extras to attach
 */
public static void send_broadcast(Context context, String broadcast, String permission, Bundle bundle) {
    //SettingsClass.log_me(tag, "Sending broadcast " + broadcast);
    Intent i = new Intent();
    i.setAction(broadcast);
    if (bundle != null) {
        i.putExtras(bundle);
    }
    if (permission != null) {
        context.sendBroadcast(i, permission);
    } else {
        context.sendBroadcast(i);
    }
}

You should include a custom permission as well, so other apps don’t get the Broadcast, but it is not necessarily needed.

To receive the Broadcast, register a Receiver in your Activity, eg

private final BroadcastReceiver receiver = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        Bundle b = intent.getExtras();
        doSomething();
    }
};



@Override
public void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    IntentFilter filter = new IntentFilter();
    filter.addAction(YOURBROADCAST);
    registerReceiver(receiver, filter);
    [...]
}

@Override
public void onDestroy() {
    unregisterReceiver(receiver);
    super.onDestroy();
}

Also you should consider using Handlers, so your methods in the OnChangeListener call are run by the MainUI thread.

Example:

Handler mHandler = new Handler();
Runnable myCode = new Runnable(){
     @Override
     protected void onRun() {
          yourCode();
          }
     };
mHandler.run(myCode);

This has also the advantage of running the code delayed with runDelayed(), so you don’t have to use sleep, and you UI will be still responding.