Question

Listening to the “Google I/O 2012 – Doing More With Less: Being a Good Android Citizen” talk, which you can see here http://www.youtube.com/watch?v=gbQb1PVjfqM&list=PL4C6BCDE45E05F49E&index=10&feature=plpp_video i found out that since api level 14 you can override onTrimMemory if you like to do some things like reducing the memory usage. But I want to implement the ComponentCallbacks2 interface outside my Activity, in my CursorAdapter for instance. In this talk it says: use Context.registerComponentCallbacks(), but when I try to use this it requires an input parameter, like this mContext.registerComponentCallbacks(ComponentCallbacks callbacks);

How can I use this?

Now I am using this

    public class ContactItemAdapter extends ResourceCursorAdapter implements ComponentCallbacks2{ 
... ...
    @Override
    public void onTrimMemory(int level) {
        Log.v(TAG, "onTrimMemory() with level=" + level);

        // Memory we can release here will help overall system performance, and
        // make us a smaller target as the system looks for memory

        if (level >= TRIM_MEMORY_MODERATE) { // 60
            // Nearing middle of list of cached background apps; evict our
            // entire thumbnail cache
            Log.v(TAG, "evicting entire thumbnail cache");
            mCache.evictAll();

        } else if (level >= TRIM_MEMORY_BACKGROUND) { // 40
            // Entering list of cached background apps; evict oldest half of our
            // thumbnail cache
            Log.v(TAG, "evicting oldest half of thumbnail cache");
            mCache.trimToSize(mCache.size() / 2);
        }
    }
}

but onTrimMemory never gets called.

Answer 1

Since your Adapter class implements ComponentCallbacks2 already, you should be able to pass the Adapter instance as the argument to registerComponentCallbacks().

From your activity, something like this should work:

registerComponentCallbacks( mAdapter );

After that, you should receive onTrimMemory() callbacks.