A memory leak happens when memory is allocated but never freed. This means the garbage collector is not able to take out the trash once we are done with the takeout. So the memory of our app will constantly increase until no more memory can be allocated to our app, leading to OutOfMemoryError which ultimately crashes the app
Without calling the unregister method, the instance will probably keep a reference around long after the referenced object has been terminated and will thus start leaking memory. But it depends on what those listeners are registered upon.
Eg: a simple well-written OnClickListener for a button should not result in a memory leak. However, a LocationListener, registered with the LocationManager - which is a system service & keep living until device shutdown - is held by the process. Hence, even if the activity is destroyed, the listener will remain registered. If that listener is an inner class, it will continue to hold an implicit reference to the activity, and you will have a memory leak.
Inner class hold a strong implicit reference to outer enclosing class. So Activity and entire view hierachy that use inner AsyncTask (most famous, well-known case) will be leaked if it get destroyed before the AsyncTask work completed.
-> Use static nested class, send objects that needed from instance of outer class through constructor and hold inside <WeakReference>.
Also an inner class. It usually cause memory leaks by an object have reference to this anonymous class without any information about it's outer container object, when the outer container object not use anymore, but the anonymous class still alive (because of still have a reference from outside) then this anonymous class and entire outer container object leaks and cannot be GC.
-> Remember to setBackgroundResource(null) and recycle() bitmaps after use.
Can leak entire Activity + view tree when device roration.
-> Avoid static context, use getApplicationContext() for long-live object.