recyling bitmaps in OnDestroy - 'trying to use a recycled bitmap' when relaunching activity

Question

I have two simple activities A and B. The user starts B from A by pressing a button, and the user then returns to A by pressing the back button.

In the onDestroy() method of activity B I recycle some background images used in activity B. What I am trying to understand is why, when activity B is started again, I am getting 'trying to use a recycled bitmap'. Surely the bitmaps will be loaded again in the onCreate() method? like they must have been on the first time the activity was launched.

Here is my example code:

public class ActivityB extends Activity {

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);    
         setContentView(R.layout.selectionpage);    
     }  

     @Override
     public void onDestroy() {      
        ImageView iv = (ImageView) findViewById(R.id.imageView1);
        ((BitmapDrawable)iv.getDrawable()).getBitmap().recycle();
        LinearLayout ll = (LinearLayout) findViewById(R.id.linearLayout1);
        ((BitmapDrawable)ll.getBackground()).getBitmap().recycle();
        super.onDestroy();
     }
 }

The code I use to launch activity B from A

     Intent intent = new Intent(ActivityA.this, ActivityB.class);
     startActivity(intent);

selectionpage.XML :

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/linearLayout1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="@drawable/backgroundimage">

        <ImageView
            android:id="@+id/imageView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/selectionimage"/>
        </LinearLayout>                

This part may be relevant. I'm not sure. I've noticed that after launching activity B, even after it has been destroyed, I can still see an instance of my activity when analyzing the memory heap using MAT. The path to GC roots seems to go through Java.lang.Thread and ContextImpl.

Answer 1

You get that error because ImageView iv & LinearLayout ll are still pointing to recycled bitmaps. You don't need to do recycling yourself inside onDestroy(). Bitmaps will be freed when they are not needed by the system.

Answer 2

You may have a memory leak if you have a reference to the activity in a separate thread which is retaining the activity for longer than it should.

This could cause iv and ll from the old activity to still be using the bitmaps after they're recycled. You could do iv.setImageDrawable(null) and ll.setBackgroundDrawable(null), but these bitmaps are created by the system and you shouldn't need to recycle them.

I am guessing that you're trying to recycle them because you ran into memory issues? which would be better explained by the possible above mentioned leak.