Android: Viewpager and FragmentStatePageAdapter

Question

I\'m designing an app that allows users to flip between multiple pages in a ViewPager. I\'ve been struggling trying to figure out how it is possible to remove a Fragment instan

Answer 1

Here's an example of how I implemented caching in PagerAdapter. After filling the cache all future view requests are served from cache, only data is replaced.

public class TestPageAdapter extends PagerAdapter{

private int MAX_SIZE = 3;
private ArrayList> pageCache = new ArrayList>(3);


public TestPageAdapter(Context context){
    // do some initialization
}

@Override
public int getCount() {
    // number of pages
}

private void addToCache(View view){
    if (pageCache.size() < MAX_SIZE){
        pageCache.add(new SoftReference(view));
    } else {
        for(int n = (pageCache.size()-1); n >= 0; n--) {
            SoftReference cachedView = pageCache.get(n);
            if (cachedView.get() == null){
                pageCache.set(n, new SoftReference(view));
                return;
            }
        }
    }
}

private View fetchFromCache(){
    for(int n = (pageCache.size()-1);  n>= 0; n--) {
        SoftReference reference = pageCache.remove(n);
        View view = reference.get();
        if (view != null) {
            return view;
        }
    }
    return null;
}

@Override
public Object instantiateItem(View collection, int position) {
    View view = fetchFromCache();
    if (view == null) {
        // not in cache, inflate manually
        LayoutInflater inflater = (LayoutInflater) collection.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        view = inflater.inflate(R.layout.page, null);
    } 
    setData(view, position);
    ((ViewPager) collection).addView(view, 0);
    return view;         
}

private void setData(View view, int position){
    // set page data (images, text ....)
}

public void setPrimaryItem(ViewGroup container, int position, Object object) {
    currentItem = (View)object;
}

public View getCurrentItem() {
    return currentItem;
}

@Override
public boolean isViewFromObject(View view, Object object) {
    return view == ((View) object);
}

@Override
public void destroyItem(View collection, int arg1, Object view) {
    ((ViewPager) collection).removeView((View) view);
    addToCache((View) view);
}

}