Removing an entry from an Bundle (i.e. extras) doesn't seem to work in combination with the back button

Question

I have a BroadcastReceiver that listen to incoming SMS'. If the message is from a certain sender, the BroadcastReceiver starts my app with the following code:

final Intent activityIntent = new Intent(context, MainActivity.class);
activityIntent.putExtra("smsChallenge", smsText);
activityIntent.putExtra("smsSenderNumber", senderMobilNumber);
activityIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
activityIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
context.startActivity(activityIntent);

In the MainActivity of my app (i.e. in onCreate()), I extract the value smsChallenge out of the intent and DELETE IT AFTER THE EXTRACTION with the following code:

Bundle extras = getIntent().getExtras();
if (extras != null) {
    smsChallenge = extras.getString("smsChallenge");
    extras.remove("smsChallenge");
}

So my app gets started from the SMS and runs fine... But if I choose to press the BACK button and restart the application (i.e. through the Taskmanager), the value smsChallenge is still in the bundle extras. This means, my restarted app thinks that it is re-started because of a new SMS which is not true...

Any ideas why removing the key-value from the bundle doesn't seem to work when using the BACK button and restarting the app again?

Answer 1

Because getExtras() creates a copy of intent extras.

You have to do like this

getIntent().removeExtra("smsChallenge");

Docs : http://developer.android.com/reference/android/content/Intent.html#removeExtra(java.lang.String)

Answer 2

I think that you can not fix this behavior because by the time you get access to the intent, the os would have already saved the intent for later launch via recent apps.

1. You can either add a flag to remove from recent apps, but in that way the app will not appear in the recent apps.
2. Add in persistent storage the last sms that was handled in your MainActivity and do this check in your onCreate, discarding an intent for an sms that was already handled.
3. A final solution would be not to send the data in the intent at all. For example, save them in a "pending" persistent storage. When your MainActivity starts, let it check for pending stuff, and clear this pending item.

Persistent storage could be SharedPreferences for example.

I would advise you to use 2 but you should count the sms received and use that counter as an id for the sms. Do not rely on the sms content and sender as an identifier for the sms.

Answer 3

"The Intent is always the original intent used to launch the activity, nothing more. This is immutable." Dianne Hackborn

To work around the problem, first make sure you declare your activity launchMode as singleTop in the manifest.

Then from the following talk, try to use onSaveInstanceState to record the fact that you have 'nulled' out some of the extras. Then in onCreate, examine its 'Bundle savedInstanceState' parameter. If it is not null, it is the Bundle you returned in the onSaveInstanceState earlier. From this Bundle, you can decide to ignore these extras or not.

Edit: In your case using shared preferences will allow you to persist state even if the activity is destroyed.

public YourActivity extends Activity {

 private boolean extrasClearedOut;
 private SharedPreferences mPrefs;
 private static String EXTRA_CLEAR_OUT = "extras_cleared_out";

 public void onCreate(Bundle savedInstanceState) {
     mPrefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext());

     extrasClearedOut = mPrefs.getBoolean(EXTRA_CLEAR_OUT, false);

     if (savedInstanceState != null && savedInstanceState.getBoolean(EXTRA_CLEAR_OUT, false))  {
         extrasClearedOut = true;
     }

     Intent intent = getIntent();
     if (extrasClearedOut) {
       // ignore the extras in the intent.

     }

     else {
       // Read and use the extras in the intent.
     }
 }

 protected void onNewIntent (Intent intent)  {
    super.onNewIntent(intent);
    setIntent(intent);

    if (extrasClearedOut) {
       // ignore the extras in the intent.
    }
    else {
       // Read and use the extras in the intent.
    }
 }

 public void someMethod(...) {
    extrasClearedOut = true;
 }

 protected void onSaveInstanceState (Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putBoolean(EXTRA_CLEAR_OUT, extrasClearedOut);
 }

 public void onDestroy()
 {
    final Editor edit = mPrefs.edit();
    edit.putBoolean(EXTRA_CLEAR_OUT, extrasClearedOut);
    edit.commit();
 }

}

Here is another working solution to your question

Answer 4

I think you need to explicitly set the intent of the activity for the behavior you want. I'm not sure why getIntent() appears to be returning a copy.

From the docs for Activity.setIntent()

Change the intent returned by getIntent(). This holds a reference to the given intent; it does not copy it. Often used in conjunction with onNewIntent(Intent).

http://developer.android.com/reference/android/app/Activity.html#setIntent(android.content.Intent)

Answer 5

private void removeExtraFromBundle(String key){
    Bundle bundle = getArguments();
    if(bundle != null){
        String value = null;
        value = bundle.getString(key);
        if(value != null){
            bundle.remove(key);
        }
    }
}

The above code will help you to remove a specific key from a bundle object.

Answer 6

My advice is adding a third extra to the intent with some nonce, e.g. just a random String:

final Intent activityIntent = new Intent(context, MainActivity.class);
activityIntent.putExtra("smsChallenge", smsText);
activityIntent.putExtra("smsSenderNumber", senderMobilNumber);
activityIntent.putExtra("nonce", UUID.randomUUID().toString);
activityIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
activityIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
context.startActivity(activityIntent);

Then check if you got this nonce before in onCreate():

public void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Intent = getIntent();
    smsChallenge = intent.getStringExtra("smsChallenge", null);
    String nonce = intent.getStringExtra("nonce", null);
    if (nonce == null) {
      // should not happen, but do something sane here
    }
    SharedPreferences sp = PreferenceManager.getDefaultPreferences(this);
    if (nonce.equals(sp.getString("nonce", null)) {
      // app was restarted
    } else {
      // app was started from a shiny fresh intent
      sp.edit().putString("nonce", nonce).commit();
    }
}

But keep in mind, that orientation changes etc. are calling onCreate() too. But you can come around that quite easily by checking if savedInstanceState is null.

Answer 7

Removing the extra is not the correct way to solve this problem. This problem is occurring due to the context that is being used to launch the said activity. Change this

final Intent activityIntent = new Intent(context, MainActivity.class);

to this

final Intent activityIntent = new Intent(context.getApplicationContext(), MainActivity.class);

the activity will now be finished when the you press the back button(provided you have not overloaded the function and changed its behavior). If you will select the application from the list of apps it will not contain any extras.

Edit:

Avoid launching activities from receiver. Consider this: You are on MainActivity. You receive sms. Now instead of the ui being updated to reflect new message you will see a new activity being launched which will not be a good user interface design.

Alternative approach: Update your database or do whatever relevant actions need to be done. Then locally broadcast the information. In your activity register a receiver for this broadcast and refresh the UI or do whatever is needed. If you want to notify the user instead of launching activity create a notification.