getApplication vs getApplicationContext

Question

I couldn t find a satisfying answer to this  so here we go  what s the deal with Activity Service getApplication   and Context getApplicationContext     In our application  both return the same object  In an ActivityTestCase however  mocking the application will make getApplication   come back with the mock  but getApplicationContext will still return a different context instance  one injected by Android   Is that a bug  Is it on purpose   I don t even understand the difference in the first place  Are there cases outside a test suite where both calls may come back with different objects  When and why  Moreover  why is getApplication defined on Activity and Service  but not on Context  Shouldn t there always be a valid application instance available from anywhere

User · Answer

To answer the question  getApplication   returns an Application object and getApplicationContext   returns a Context object   Based on your own observations  I would assume that the Context of both are identical  i e  behind the scenes the Application class calls the latter function to populate the Context portion of the base class or some equivalent action takes place    It shouldn t really matter which function you call if you just need a Context

User · Answer

Compare getApplication   and getApplicationContext     getApplication returns an Application object which will allow you to manage your global application state and respond to some device situations such as onLowMemory   and onConfigurationChanged     getApplicationContext returns the global application context - the difference from other contexts is that for example  an activity context may be destroyed  or otherwise made unavailable  by Android when your activity ends  The Application context remains available all the while your Application object exists  which is not tied to a specific Activity  so you can use this for things like Notifications that require a context that will be available for longer periods and independent of transient UI objects   I guess it depends on what your code is doing whether these may or may not be the same - though in normal use  I d expect them to be different

User · Answer

It seems to have to do with context wrapping  Most classes derived from Context are actually a ContextWrapper  which essentially delegates to another context  possibly with changes by the wrapper    The context is a general abstraction that supports mocking and proxying  Since many contexts are bound to a limited-lifetime object such as an Activity  there needs to be a way to get a longer-lived context  for purposes such as registering for future notifications  That is achieved by Context getApplicationContext    A logical implementation is to return the global Application object  but nothing prevents a context implementation from returning a wrapper or proxy with a suitable lifetime instead   Activities and services are more specifically associated with an Application object  The usefulness of this  I believe  is that you can create and register in the manifest a custom class derived from Application and be certain that Activity getApplication   or Service getApplication   will return that specific object of that specific type  which you can cast to your derived Application class and use for whatever custom purpose    In other words  getApplication   is guaranteed to return an Application object  while getApplicationContext   is free to return a proxy instead

User · Answer

Very interesting question  I think it s mainly a semantic meaning  and may also be due to historical reasons   Although in current Android Activity and Service implementations  getApplication   and getApplicationContext   return the same object  there is no guarantee that this will always be the case  for example  in a specific vendor implementation    So if you want the Application class you registered in the Manifest  you should never call getApplicationContext   and cast it to your application  because it may not be the application instance  which you obviously experienced with the test framework    Why does getApplicationContext   exist in the first place    getApplication   is only available in the Activity class and the Service class  whereas getApplicationContext   is declared in the Context class   That actually means one thing   when writing code in a broadcast receiver  which is not a context but is given a context in its onReceive method  you can only call getApplicationContext    Which also means that you are not guaranteed to have access to your application in a BroadcastReceiver   When looking at the Android code  you see that when attached  an activity receives a base context and an application  and those are different parameters  getApplicationContext   delegates it s call to baseContext getApplicationContext     One more thing   the documentation says that it most cases  you shouldn t need to subclass Application       There is normally no need to subclass Application  In most situation    static singletons can provide the same functionality in a more modular   way  If your singleton needs a global context  for example to register   broadcast receivers   the function to retrieve it can be given a   Context which internally uses Context getApplicationContext   when   first constructing the singleton    I know this is not an exact and precise answer  but still  does that answer your question

[android] getApplication() vs. getApplicationContext()

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