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How do I programmatically "restart" an Android app?

Posted by: admin March 10, 2020 Leave a comment

Questions:

Firstly, I know that one should not really kill/restart an application on Android. In my use case I want to factory-reset my application in a specific case where a server sends a specific information to the client.

The user can only be logged in on the server with ONE instance of the application (i.e. multiple devices are not allowed). If another instance gets that “logged-in”-lock then all other instances of that user have to delete their data (factory-reset), to maintain consistency.

It is possible to forcibly get the lock, because the user might delete the app and reinstall it which would result in a different instance-id and the user would not be able to free the lock any more. Therefore it is possible to forcibly get the lock.

Because of that force-possibility we need to always check in an concrete instance that it has the lock. That is done on (almost) each request to the server. The server might send a “wrong-lock-id”. If that is detected, the client application must delete everything.


That was the use-case.

I have an Activity A that starts the Login Activity L or the app’s main Activity B depending on a sharedPrefs value. After starting L or B it closes itself so that only L or B is running. So in the case that the user is logged in already B is running now.

B starts C. C calls startService for the IntentService D. That results in this stack:

(A) > B > C > D

From the onHandleIntent method of D an event is send to a ResultReceiver R.

R now handles that event by providing the user a dialog where he can choose to factory-reset the application (delete the database, sharedPrefs, etc.)

After the factory-reset I want to restart the application (to close all activities) and only start A again which then launches the login Activity L and finishes itself:

(A) > L

The Dialog’s onClick-method looks like this:

@Override
public void onClick(DialogInterface dialog, int which) {

    // Will call onCancelListener
    MyApplication.factoryReset(); // (Deletes the database, clears sharedPrefs, etc.)
    Intent i = new Intent(MyApp.getContext(), A.class);
    i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    MyApp.getContext().startActivity(i);
}

And that’s the MyApp class:

public class MyApp extends Application {
    private static Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        context = getApplicationContext();
    }

    public static Context getContext() {
        return context;
    }

    public static void factoryReset() {
        // ...
    }
}

The problem is if I use the FLAG_ACTIVITY_NEW_TASK the Activities B and C are still running. If I hit the back button on the login Activity I see C, but I want to go back to the home screen.

If I do not set the FLAG_ACTIVITY_NEW_TASK I get the error:

07-07 12:27:12.272: ERROR/AndroidRuntime(9512): android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?

I cannot use the Activities’ Context, because the ServiceIntent D might also be called from an background task which is started by the AlarmManager.

So how could I solve this to the activity stack becoming (A) > L?

How to&Answers:

You can use PendingIntent to setup launching your start activity in the future and then close your application

Intent mStartActivity = new Intent(context, StartActivity.class);
int mPendingIntentId = 123456;
PendingIntent mPendingIntent = PendingIntent.getActivity(context, mPendingIntentId,    mStartActivity, PendingIntent.FLAG_CANCEL_CURRENT);
AlarmManager mgr = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 100, mPendingIntent);
System.exit(0);

Answer:

You can simply call:

public static void triggerRebirth(Context context, Intent nextIntent) {
    Intent intent = new Intent(context, YourClass.class);
    intent.addFlags(FLAG_ACTIVITY_NEW_TASK);
    intent.putExtra(KEY_RESTART_INTENT, nextIntent);
    context.startActivity(intent);
    if (context instanceof Activity) {
      ((Activity) context).finish();
    }

    Runtime.getRuntime().exit(0);
}

Which is used in the ProcessPhoenix library


As an alternative:

Here’s a bit improved version of @Oleg Koshkin answer.

If you really want to restart your activity including a kill of the current process, try following code. Place it in a HelperClass or where you need it.

public static void doRestart(Context c) {
        try {
            //check if the context is given
            if (c != null) {
                //fetch the packagemanager so we can get the default launch activity 
                // (you can replace this intent with any other activity if you want
                PackageManager pm = c.getPackageManager();
                //check if we got the PackageManager
                if (pm != null) {
                    //create the intent with the default start activity for your application
                    Intent mStartActivity = pm.getLaunchIntentForPackage(
                            c.getPackageName()
                    );
                    if (mStartActivity != null) {
                        mStartActivity.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                        //create a pending intent so the application is restarted after System.exit(0) was called. 
                        // We use an AlarmManager to call this intent in 100ms
                        int mPendingIntentId = 223344;
                        PendingIntent mPendingIntent = PendingIntent
                                .getActivity(c, mPendingIntentId, mStartActivity,
                                        PendingIntent.FLAG_CANCEL_CURRENT);
                        AlarmManager mgr = (AlarmManager) c.getSystemService(Context.ALARM_SERVICE);
                        mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 100, mPendingIntent);
                        //kill the application
                        System.exit(0);
                    } else {
                        Log.e(TAG, "Was not able to restart application, mStartActivity null");
                    }
                } else {
                    Log.e(TAG, "Was not able to restart application, PM null");
                }
            } else {
                Log.e(TAG, "Was not able to restart application, Context null");
            }
        } catch (Exception ex) {
            Log.e(TAG, "Was not able to restart application");
        }
    }

This will also reinitialize jni classes and all static instances.

Answer:

Jake Wharton recently published his ProcessPhoenix library, which does this in a reliable way. You basically only have to call:

ProcessPhoenix.triggerRebirth(context);

The library will automatically finish the calling activity, kill the application process and restart the default application activity afterwards.

Answer:

I have slightly modified Ilya_Gazman answer to use new APIs (IntentCompat is deprecated starting API 26). Runtime.getRuntime().exit(0) seems to be better than System.exit(0).

 public static void triggerRebirth(Context context) {
    PackageManager packageManager = context.getPackageManager();
    Intent intent = packageManager.getLaunchIntentForPackage(context.getPackageName());
    ComponentName componentName = intent.getComponent();
    Intent mainIntent = Intent.makeRestartActivityTask(componentName);
    context.startActivity(mainIntent);
    Runtime.getRuntime().exit(0);
}

Answer:

IntentCompat.makeRestartActivityTask

The new way of doing it, is by using IntentCompat.makeRestartActivityTask

Make an Intent that can be used to re-launch an application’s task in
its base state. This is like makeMainActivity(ComponentName), but also
sets the flags Intent.FLAG_ACTIVITY_NEW_TASK and
FLAG_ACTIVITY_CLEAR_TASK.

PackageManager packageManager = context.getPackageManager();
Intent intent = packageManager.getLaunchIntentForPackage(context.getPackageName());
ComponentName componentName = intent.getComponent();
Intent mainIntent = IntentCompat.makeRestartActivityTask(componentName);
context.startActivity(mainIntent);
System.exit(0);

Answer:

There is a really nice trick. My problem was that some really old C++ jni library leaked resources. At some point, it stopped functioning. The user tried to exit the app and launch it again — with no result, because finishing an activity is not the same as finishing (or killing) the process. (By the way, the user could go to the list of the running applications and stop it from there — this would work, but the users just do not know how to terminate applications.)

If you want to observe the effect of this feature, add a static variable to your activity and increment it each, say, button press. If you exit the application activity and then invoke the application again, this static variable will keep its value. (If the application really was exited, the variable would be assigned the initial value.)

(And I have to comment on why I did not want to fix the bug instead. The library was written decades ago and leaked resources ever since. The management believes it always worked. The cost of providing a fix instead of a workaround… I think, you get the idea.)

Now, how could I reset a jni shared (a.k.a. dynamic, .so) library to the initial state?
I chose to restart application as a new process.

The trick is that System.exit() closes the current activity and Android recreates the application with one activity less.

So the code is:

/** This activity shows nothing; instead, it restarts the android process */
public class MagicAppRestart extends Activity {
    // Do not forget to add it to AndroidManifest.xml
    // <activity android:name="your.package.name.MagicAppRestart"/>
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        System.exit(0);
    }
    public static void doRestart(Activity anyActivity) {
        anyActivity.startActivity(new Intent(anyActivity.getApplicationContext(), MagicAppRestart.class));
    }
}

The calling activity just executes the code MagicAppRestart.doRestart(this);, the calling activity’s onPause() is executed, and then the process is re-created. And do not forget to mention this activity in AndroidManifest.xml

The advantage of this method is that there is no delays.

UPD: it worked in Android 2.x, but in Android 4 something has changed.

Answer:

My solution doesn’t restart the process/application. It only lets the app “restart” the home activity (and dismiss all other activities). It looks like a restart to users, but the process is the same. I think in some cases people want to achieve this effect, so I just leave it here FYI.

public void restart(){
    Intent intent = new Intent(this, YourHomeActivity.class);
    this.startActivity(intent);
    this.finishAffinity();
}

Answer:

Ok, I refactored my app and I will not finish A automatically. I let this run always and finish it through the onActivityResult event.
In this way I can use the FLAG_ACTIVITY_CLEAR_TOP + FLAG_ACTIVITY_NEW_TASK flags to get what I want:

public class A extends Activity {

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        finish();
    }

    protected void onResume() {
        super.onResume();
        // ...
        if (loggedIn) {
            startActivityForResult(new Intent(this, MainActivity.class), 0);
        } else {
            startActivityForResult(new Intent(this, LoginActivity.class), 0);
        }
    }
}

and in the ResultReceiver

@Override
public void onClick(DialogInterface dialog, int which) {
    MyApp.factoryReset();
    Intent i = new Intent(MyApp.getContext(), A.class);
    i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    MyApp.getContext().startActivity(i);
}

Thanks anyway!

Answer:

Intent i = getBaseContext().getPackageManager().getLaunchIntentForPackage( getBaseContext().getPackageName() );
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);

Answer:

The only code that did not trigger “Your app has closed unexpectedly” is as follows. It’s also non-deprecated code that doesn’t require an external library. It also doesn’t require a timer.

public static void triggerRebirth(Context context, Class myClass) {
    Intent intent = new Intent(context, myClass);
    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
    context.startActivity(intent);
    Runtime.getRuntime().exit(0);
}

Answer:

The best way to fully restart an app is to relaunch it, not just to jump to an activity with FLAG_ACTIVITY_CLEAR_TOP and FLAG_ACTIVITY_NEW_TASK. So my solution is to do it from your app or even from another app, the only condition is to know the app package name (example: ‘com.example.myProject‘)

 public static void forceRunApp(Context context, String packageApp){
    Intent launchIntent = context.getPackageManager().getLaunchIntentForPackage(packageApp);
    launchIntent.setFlags(Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS | Intent.FLAG_ACTIVITY_NEW_TASK);
    context.startActivity(launchIntent);
}

Example of usage restart or launch appA from appB:

forceRunApp(mContext, "com.example.myProject.appA");

You can check if the app is running:

 public static boolean isAppRunning(Context context, String packageApp){
    ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
    List<ActivityManager.RunningAppProcessInfo> procInfos = activityManager.getRunningAppProcesses();
    for (int i = 0; i < procInfos.size(); i++) {
        if (procInfos.get(i).processName.equals(packageApp)) {
           return true;
        }
    }
    return false;
}

Note: I know this answer is a bit out of topic, but it can be really helpful for somebody.

Answer:

My best way to restart application is to use finishAffinity();
Since, finishAffinity(); can be used on JELLY BEAN versions only, so we can use ActivityCompat.finishAffinity(YourCurrentActivity.this); for lower versions.

Then use Intent to launch first activity, so the code will look like this:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
    finishAffinity();
    Intent intent = new Intent(getApplicationContext(), YourFirstActivity.class);
    startActivity(intent);
} else {
    ActivityCompat.finishAffinity(YourCurrentActivity.this);
    Intent intent = new Intent(getApplicationContext(), YourFirstActivity.class);
    startActivity(intent);
}

Hope it helps.

Answer:

I’ve found that this works on API 29 and later – for the purpose of killing and restarting the app as if the user had launched it when it wasn’t running.

public void restartApplication(final @NonNull Activity activity) {
   // Systems at 29/Q and later don't allow relaunch, but System.exit(0) on
   // all supported systems will relaunch ... but by killing the process, then
   // restarting the process with the back stack intact. We must make sure that
   // the launch activity is the only thing in the back stack before exiting.
   final PackageManager pm = activity.getPackageManager();
   final Intent intent = pm.getLaunchIntentForPackage(activity.getPackageName());
   activity.finishAffinity(); // Finishes all activities.
   activity.startActivity(intent);    // Start the launch activity
   System.exit(0);    // System finishes and automatically relaunches us.
}

That was done when the launcher activity in the app has this:

<intent-filter>
    <action android:name="android.intent.action.VIEW"/>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
</intent-filter>

I’ve seen comments claiming that a category of DEFAULT is needed, but I haven’t found that to be the case. I have confirmed that the Application object in my app is re-created, so I believe that the process really has been killed and restarted.

The only purpose for which I use this is to restart the app after the user has enabled or disabled crash reporting for Firebase Crashlytics. According to their docs, the app has to be restarted (process killed and re-created) for that change to take effect.

Answer:

Try using FLAG_ACTIVITY_CLEAR_TASK

Answer:

Here is an example to restart your app in a generic way by using the PackageManager:

Intent i = getBaseContext().getPackageManager()
             .getLaunchIntentForPackage( getBaseContext().getPackageName() );
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);

Answer:

try this:

Intent intent = getPackageManager().getLaunchIntentForPackage(getPackageName());
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);

Answer:

Directly start the Initial Screen with FLAG_ACTIVITY_CLEAR_TASK and FLAG_ACTIVITY_NEW_TASK.

Answer:

I had to add a Handler to delay the exit:

 mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 200, mPendingIntent);
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                Runtime.getRuntime().exit(0);
            }
        }, 100);

Answer:

Use:

navigateUpTo(new Intent(this, MainActivity.class));

It works starting from API level 16 (4.1), I believe.

Answer:

You can use startInstrumentation method of Activity. You need implement empty Instrumentation and pointed in manifest. After that you can call this method for restart your app. Like this:

try {           
    InstrumentationInfo info = getPackageManager().queryInstrumentation(getPackageName(), 0).get(0);
    ComponentName component = new ComponentName(this, Class.forName(info.name));
    startInstrumentation(component, null, null);
} catch (Throwable e) {             
    new RuntimeException("Failed restart with Instrumentation", e);
}

I get Instrumentation class name dynamically but you can hardcode it. Some like this:

try {           
    startInstrumentation(new ComponentName(this, RebootInstrumentation.class), null, null); 
} catch (Throwable e) {             
    new RuntimeException("Failed restart with Instrumentation", e);
}

Call startInstrumentation make reload of your app. Read description of this method. But it can be not safe if acting like kill app.

Answer:

The application I’m working on has to give the user the possibility to choose which fragments to display (fragments are dynamically changed at run-time). The best solution for me was to restart completely the application.

So I tried plenty of solutions and none of them has worked for me, but this:

final Intent mStartActivity = new Intent(SettingsActivity.this, Splash.class);
final int mPendingIntentId = 123456;
final PendingIntent mPendingIntent = PendingIntent.getActivity(SettingsActivity.this, mPendingIntentId, mStartActivity,
                    PendingIntent.FLAG_CANCEL_CURRENT);
final AlarmManager mgr = (AlarmManager) SettingsActivity.this.getSystemService(Context.ALARM_SERVICE);
mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 100, mPendingIntent);
this.finishAffinity(); //notice here
Runtime.getRuntime().exit(0); //notice here

Hoping that is going to help someone else!

Answer:

try this:

private void restartApp() {
    Intent intent = new Intent(getApplicationContext(), YourStarterActivity.class);
    int mPendingIntentId = MAGICAL_NUMBER;
    PendingIntent mPendingIntent = PendingIntent.getActivity(getApplicationContext(), mPendingIntentId, intent, PendingIntent.FLAG_CANCEL_CURRENT);
    AlarmManager mgr = (AlarmManager) getApplicationContext().getSystemService(Context.ALARM_SERVICE);
    mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 100, mPendingIntent);
    System.exit(0);
}

Answer:

With the Process Phoenix library. The Activity you want to relaunch is named “A”.

Java flavor

// Java
public void restart(){
    Intent nextIntent = new Intent(this, A.class);
    ProcessPhoenix.triggerRebirth(this, nextIntent);
}

Kotlin flavor

// kotlin
fun restart() {
    val nextIntent = Intent(this, A::class.java)
    ProcessPhoenix.triggerRebirth(this, nextIntent)
}

Answer:

You can restart your current activity like this:

Fragment :

activity?.recreate()

Activity :

recreate()