Implementing ViewHolder pattern on a ListView that includes ViewPager

Question

I have a layout which includes a ViewPager among other, simpler Views. I am using this layout as a list item for a ListView and it works fine. But when I try to implement a ViewHolder pattern, the application crashes when I scroll down. The error occurs when I set the adapter to the view pager.

The adapter without the ViewHolder implementation:

public class FaceInSandAdapter extends ArrayAdapter<Gem> {
private Context mContext;

    public FaceInSandAdapter(Context c, ArrayList<Gem> gems) {
    super(c, 0, gems);
    mContext = c;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
    final Gem gem = getItem(position);

    convertView = ((Activity) mContext).getLayoutInflater().inflate(
            R.layout.list_item_gem, null);
    final ViewPager pager = (ViewPager) convertView
            .findViewById(R.id.list_item_gem_photosViewPager);
    pager.setId(gem.getId());

    pager.setAdapter(new PhotoSliderPagerAdapter(((FragmentActivity) parent
        .getContext()).getSupportFragmentManager(), gem.getImageUrls()));

    TextView address = (TextView) convertView
        .findViewById(R.id.list_item_gem_addressTextView);

    address.setText(gem.getAddress());
    return convertView;

    }
}

How do I correctly implement a ViewHolder pattern for the adapter that inflates a layout which contains a ViewPager? The following is my attempt at implementing such adapter, which gives the above mentioned error:

public class FaceInSandAdapter extends ArrayAdapter<Gem> {
private Context mContext;

public FaceInSandAdapter(Context c, ArrayList<Gem> gems) {
    super(c, 0, ads);
    mContext = c;
}

static class ViewHolder {
    ViewPager pager;
    TextView address;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    final ViewHolder holder;

    final Gem gem = getItem(position);

    if (convertView == null) {
        convertView = ((Activity) mContext).getLayoutInflater().inflate(
                R.layout.list_item_gem, null);

        holder = new ViewHolder();
        holder.pager = (ViewPager) convertView
                .findViewById(R.id.list_item_gem_photosViewPager);


        holder.address = (TextView) convertView
                .findViewById(R.id.list_item_gem_addressTextView);

        convertView.setTag(holder);

    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    FragmentManager fm = ((FragmentActivity) convertView.getContext())
            .getSupportFragmentManager();
    holder.pager.setId(gem.getId());
    holder.pager.setAdapter(new PhotoSliderPagerAdapter(fm, gem
            .getImageUrls()));

    holder.address.setText(gem.getAddress());

    return convertView;

    }
}

EDIT

Stacktrace for the error I get with my implementation of ViewHolder pattern:

FATAL EXCEPTION: main
Process: xx.yyy.zzzzzz, PID: 5010
android.content.res.Resources$NotFoundException: Unable to find resource ID #0x3fe1
at android.content.res.Resources.getResourceName(Resources.java:1776)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:919)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
 at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
at android.support.v4.view.ViewPager.setAdapter(ViewPager.java:442)
at xxx.xxx.xxx.FaceInSandAdapter.getView(FaceInSandAdapter.java:89)
at android.widget.AbsListView.obtainView(AbsListView.java:2240)
at android.widget.ListView.makeAndAddView(ListView.java:1790)
at android.widget.ListView.fillDown(ListView.java:691)
at android.widget.ListView.fillGap(ListView.java:655)
at android.widget.AbsListView.trackMotionScroll(AbsListView.java:5136)
at android.widget.AbsListView$FlingRunnable.run(AbsListView.java:4247)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
at android.view.Choreographer.doCallbacks(Choreographer.java:574)
at android.view.Choreographer.doFrame(Choreographer.java:543)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5102)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)

**EDIT 2 **

Now, as the viepager is working as a listview item, the problem that remains is that I am instantiating ImageViews, having a bare bones implementation of the PagerAdapter (no saving state, no limiting offscreen views), so the list ends up using big amount of memory.

Answer 1

After trying a few alternatives, like a HorizontalScrollView or some external libraries, I still came back to how I was implementing this from the beginning. I solved this problem by extending the PagerAdapter directly instead of FragmentStatePagerAdapter, and overriding instantiateItem. The problem was with using the fragments, and it seems obvious now: Using FragmentStatePagerAdapter was really unneeded, as I was just trying to make a photo slider, so using fragments was unnecessary.

Here is my code for the new PhotoPagerAdapter:

public class PhotoPagerAdapter extends PagerAdapter {
private Context mContext;
private List<String> mUrls;

public PhotoPagerAdapter(Context context, List<String> urls) {
    mContext = context;
    mUrls = urls;
}

@Override
public int getCount() {
    return mUrls.size();
}

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

@Override
public Object instantiateItem(ViewGroup container, int position) {
    ImageView imgDisplay;

    LayoutInflater inflater = (LayoutInflater) mContext
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View v = inflater.inflate(R.layout.fragment_gem_photo, container, false);

    imgDisplay = (ImageView) v
            .findViewById(R.id.fragment_gem_photo_imageView);
    Picasso.with(mContext).load(mUrls.get(position))
            .placeholder(R.drawable.wait_image).into(imgDisplay);
    ((ViewPager) container).addView(v);

    return v;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    ((ViewPager) container).removeView((RelativeLayout) object);

}
}

EDIT

I figured out the problem isn't with the incorrect implementation of the ViewHolder pattern at all. Instead, it is with reusing the already inflated convertView when it contains a viewpager with the FragmentStatePagerAdapter.

Answer 2

Read the stacktrace you posted:

android.content.res.Resources$NotFoundException: Unable to find resource ID #0x3fe1

There seems to be an id you are referencing that does not exist. This is causing you app to crash, not the holder pattern.