Android - Preventing common memory leaks
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The document discusses common causes of and solutions to memory leaks in Android applications. It covers issues related to using the correct Context, holding references to activities from outside their scope, non-static inner classes holding implicit references to their outer class, threads not being garbage collected, and forgetting to recycle bitmaps. The key recommendations are to always use Application Context when possible, avoid leaking references between scopes, make handlers and inner classes static when possible, implement cancellation for threads, and properly recycle bitmaps.
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Android - Preventing common memory leaks
- 1. Preventing memory leaks Ali Muzaffar
- 2. Common causes of memory leaks Which Context to use? Application Context Activity Context Problem with references outside of context Why should Handlers be static? Should inner classes be static? Recycle bitmaps
- 3. Common causes of memory leaks Which Context to use? Application Context Activity Context Problem with references outside of context Why should Handlers be static? Should inner classes be static? Leaking Threads Also, Recycling Bitmaps (not covered here).
- 4. Which Context? Which is better? 1. new ArrayAdapter(this, android.R.layout.simple_list_item_1, list); 2. new ArrayAdapter(getApplicationContext(), android.R.layout.simple_list_item_1, list); 3. new ArrayAdapter(getBaseContext(), android.R.layout.simple_list_item_1, list); 1. new TextView(this); 2. new TextView(getApplicationContext()); 3. new TextView(getBaseContext());
- 5. Which is better? 1. new ArrayAdapter(this, android.R.layout.simple_list_item_1, list); 2. new ArrayAdapter(getApplicationContext(), android.R.layout.simple_list_item_1, list); 3. new ArrayAdapter(getBaseContext(), android.R.layout.simple_list_item_1, list); 1. new TextView(this); 2. new TextView(getApplicationContext()); 3. new TextView(getBaseContext());
- 6. Good rule of thumb Always use Application Context. Use Activity where necessary. Meaning the object will be collected with the Activity or method specifically requests it. Never use getBaseContext().
- 7. Problem with references outside context Why using the right context is important? Threads & Garbage Collection How do we fix this?
- 8. Usually not a problem @Override protected void onCreate(Bundle state) { super.onCreate(state); TextView label = new TextView(this); label.setText("Leaks are bad"); setContentView(label); } //Code by Romain Guy
- 9. Now it’s a problem private static Drawable sBackground; @Override protected void onCreate(Bundle state) { super.onCreate(state); TextView label = new TextView(this); label.setText("Leaks are bad"); if (sBackground == null) { sBackground = getDrawable(R.drawable.large_bitmap); } label.setBackgroundDrawable(sBackground); setContentView(label); } //Code by Romain Guy Drawables hold references to the Activity. TextView holds a strong reference to the Activity. The Drawable is not garbage collected, as a result, neither is the TextView or the Activity.
- 10. The problem with non-static inner classes Why do I get this error?
- 11. Consider this piece of code
- 12. So whats the issue with non-static inner classes When an Android application first starts, the framework creates a Looper object for the application's main thread. A Looper implements a simple message queue, processing Message objects in a loop one after another. All major application framework events (such as Activity lifecycle method calls, button clicks, etc.) are contained inside Message objects, which are added to the Looper's message queue and are processed one-by-one. The main thread's Looper exists throughout the application's lifecycle. When a Handler is instantiated on the main thread, it is associated with the Looper's message queue. Messages posted to the message queue will hold a reference to the Handler so that the framework can call Handler#handleMessage(Message) when the Looper eventually processes the message. In Java, non-static inner and anonymous classes hold an implicit reference to their outer class. Static inner classes, on the other hand, do not.
- 13. So what’s the issue with Threads? Threads can be leaked along with/without memory. Why? Threads in Java are GC roots; that is, the Dalvik Virtual Machine (DVM) keeps hard references to all active threads in the runtime system, and as a result, threads that are left running will never be eligible for garbage collection.
- 14. Crouton Why do we have to call Crouton.cancelAllCroutons() ?
- 15. Crouton Why do we have to call Crouton.cancelAllCroutons() ?
- 16. What can we do? Do not reference anything outside of it’s scope. Try to not have long living objects. Don’t assume java will clean up your threads. Implement cancellation policies for background threads. WeakReference
- 17. Egg-xample!