Question

Several classes in Android API require a Context parameter in their constructor, for example ArrayAdapter, SQLiteOpenHelper or Intent. When creating such an object from inside an Activity, what context instance is more appropriate to pass to them: this (the activity instance itself) or the object returned by the activity’s getApplicationContext() method and why?

Up to now, I have used both and didn’t see any difference in the resulting functionality. Is there any rule of thumb?

Answer 1

From the docs of getApplicationContext() method:

Return the context of the single, global Application object of the
current process. This generally should only be used if you need a
Context whose lifecycle is separate from the current context, that is
tied to the lifetime of the process rather than the current component.

Consider for example how this interacts with {@ #registerReceiver(BroadcastReceiver, IntentFilter)}:

• If used from an Activity context, the receiver is being registered
  within that activity. This means that you are expected to unregister
  before the activity is done being destroyed; in fact if you do not do
  so, the framework will clean up your leaked registration as it removes
  the activity and log an error. Thus, if you use the Activity context
  to register a receiver that is static (global to the process, not
  associated with an Activity instance) then that registration will be
  removed on you at whatever point the activity you used is destroyed.

• If used from the Context returned here, the receiver is being
  registered with the global state associated with your application.
  Thus it will never be unregistered for you. This is necessary if the
  receiver is associated with static data, not a particular component.
  However using the ApplicationContext elsewhere can easily lead to
  serious leaks if you forget to unregister, unbind, etc.