Application class lifecycle while service is running

Question

I am developing an application with custom Application class which initializes a couple of singletons so they live during all application working time. I also have a couple of services in my application which work with these singletons. Is it possible situation that Application class will be destroyed by android with singletons' instances before services so services will not be able to use them? Or application lives always even for services of it's context? What is the best way to find a way out of this situation?

Thanks.

score 9 · Accepted Answer · answered Apr 22 '13 at 11:12

Regarding the application object:

The application object is the main absolute starting point on any Android app. It will always exist before any of the Manifest declared items such as Activity, Service and BroadcastReceiver. So relax that the singletons will be there for you.

Regarding the singleton paradigma:

That's a big discussion topic, you can google more about it so what follows is my personal opinion on it. Whatever is the reason for your singletons (a database, an bitmap caching, a FileUtils) I think it's ok and correct to initialise them on the very first point of entry of your app, which is the Application. But the application itself is not an object meant to carry or hold those objects, that way my suggested design approach is to:

=> on your singleton object/class you'll have to:

private static MySingletonClass instance; // reference to the single object
private MySingletonClass(Context c){ // private constructor to avoid construction from anywhere else
    // let's say it needs the context for construction because it's a database singleton
}
public static MySingletonClass get(){ // 
    if(instance == null) throw new RuntimeException("This singleton must be initialised before anything else");
    return instance;
}
public static void init(Context c){ // call the initialisation from the Application
   instance = new MySingletonClass(c);
}

=> and then on your Application object you simply init the singleton

onCreate(){
   MySingletonClass.init(getApplicationContext());
}

with that way you'll keep the necessary initialisation, enforce the singleton pattern but to access the object you call to that object class not to the application. I know it's just a organisational difference, but I believe that that's what separate good and bad code.

So for example on your service the call is: MySingletonClass.get() and should never be MyApplication.mySingle.

hope it helps.

Yes, I have code like this now. But sometimes I don't know why my service throws NullPointerException when I trying to use singleton's field in here for example.. — pavelkorolevxyz, Apr 22 '13 at 14:00
that's why I include the `throw new RuntimeException` line. That way you can be sure that it's failing because of that or something else. Other way is to absolutely be sure, even if the GC kills it, because service does have Context, you could on the `init()` put a code `if(instance==null)` to only initialise if necessary and call init from the service too. — Budius, Apr 22 '13 at 14:05

score 4 · Answer 2 · answered Apr 22 '13 at 11:02

From my understanding service can't live without application context, service is bound to the application with the Context reference so I think if the application is killed also the Context is killed and that lead that all components are been killed,

you can read here for more info

http://developer.android.com/guide/components/fundamentals.html#proclife

Application class lifecycle while service is running

2 Answers2