android - How do I implement view recycling mechanism for PagerAdapter?

Question

I have a pager adapter that suppose to inflate a complex view representing a calendar.

It takes around ~350 ms to inflate each year of the calendar.

To improve performance I would like to implement the same mechanism that exists in the ListView array adapter of recycling views (convertView parameter in getView()).

Here is my current getView() from the adapter.

@Override
protected View getView(VerticalViewPager pager, final DateTileGrid currentDataItem, int position)
{
    mInflater = LayoutInflater.from(pager.getContext());

        // This is were i would like to understand weather is should use a recycled view or create a new one.
    View datesGridView = mInflater.inflate(R.layout.fragment_dates_grid_page, pager, false);


    DateTileGridView datesGrid = (DateTileGridView) datesGridView.findViewById(R.id.datesGridMainGrid);
    TextView yearTitle = (TextView) datesGridView.findViewById(R.id.datesGridYearTextView);
    yearTitle.setText(currentDataItem.getCurrentYear() + "");
    DateTileView[] tiles = datesGrid.getTiles();

    for (int i = 0; i < 12; i++)
    {
        String pictureCount = currentDataItem.getTile(i).getPictureCount().toString();
        tiles[i].setCenterLabel(pictureCount);
        final int finalI = i;
        tiles[i].setOnCheckedChangeListener(new DateTileView.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(DateTileView tileChecked, boolean isChecked)
            {
                DateTile tile = currentDataItem.getTile(finalI);
                tile.isSelected(isChecked);
            }
        });
    }

    return datesGridView;
}

Any pointers or direction for implementing such a behavior? In particular how can I know in the adapter that one of the DateTileGridViews is being swiped of the screen so I could save it in memory to reuse it next time.

Answer 1

So I have figured it out.

1. overwrite destroyItem(ViewGroup container, int position, Object view) ans save you cached view
2. create a separate method to see if there is any chance to use a recycled view or should you inflate a new one.
3. remember to remove the recycled view from cache once its been used to avoid having same view attaching same view to the pager.

here is the code.. I used a Stack of view to cache all removed views from my pager

private View inflateOrRecycleView(Context context)
{

    View viewToReturn;
    mInflater = LayoutInflater.from(context);
    if (mRecycledViewsList.isEmpty())
    {
        viewToReturn = mInflater.inflate(R.layout.fragment_dates_grid_page, null, false);
    }
    else
    {
        viewToReturn = mRecycledViewsList.pop();
        Log.i(TAG,"Restored recycled view from cache "+ viewToReturn.hashCode());
    }


    return viewToReturn;
}

@Override
public void destroyItem(ViewGroup container, int position, Object view)
{
    VerticalViewPager pager = (VerticalViewPager) container;
    View recycledView = (View) view;
    pager.removeView(recycledView);
    mRecycledViewsList.push(recycledView);
    Log.i(TAG,"Stored view in cache "+ recycledView.hashCode());
}

do not forget to instantiate the stack in the adapter constructor.