Fix etsy's staggered grid view when one column is higher than the other by more than grid view height. https://github.com/etsy/AndroidStaggeredGrid/issues/66

fragment_grid_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_height="wrap_content"
    android:layout_width="match_parent">

    <LinearLayout
        android:id="@+id/content"
        style="@style/GridItem">

        <com.etsy.android.grid.util.DynamicHeightImageView
            android:id="@+id/image"
            style="@style/Image.FullWidth" />

        <TextView
            android:id="@+id/title"
            style="@style/GridItem.PrimaryHeader" />

        <TextView
            android:id="@+id/description"
            style="@style/GridItem.Text" />
    </LinearLayout>
</LinearLayout>

GridHeightPlaceholder.java

package no.bstcm.loyaltyapp.core.util;

import android.view.View;
import android.widget.AbsListView;

import com.etsy.android.grid.StaggeredGridView;

import no.bstcm.loyaltyapp.core.R;

/**
 * Grid library has a very interesting bug related to how views are recycled.
 * If last item is higher than grid view, then other column disappears
 * or is weirdly moved.
 *
 * To fix that let's display a placeholder that ensures that columns have the same height
 * in case the difference between them is greater than grid view height.
 *
 * Issues:
 * @see https://github.com/etsy/AndroidStaggeredGrid/issues/21
 * @see https://github.com/etsy/AndroidStaggeredGrid/issues/66
 *
 * Example:
 * How to alter adapter to use it?
 *
 * public class GridAdapter extends ArrayAdapter<...>
 *       implements GridHeightPlaceholder.AdapterCallbacks {
 *
 *    private StaggeredGridView lookupView;
 *    private final GridHeightPlaceholder placeholder;
 *
 *    public GridAdapter(Context context, List<...> list) {
 *       super(context, R.layout.fragment_grid_item, list);
 *       placeholder = new GridHeightPlaceholder(this);
 *    }
 *
 *    public void setLookupView(StaggeredGridView lookupView) {
 *       this.lookupView = lookupView;
 *       if (lookupView != null) {
 *          placeholder.listenToScroll();
 *       } else {
 *          placeholder.stopListeningToScroll();
 *          placeholder.onDetach();
 *       }
 *    }
 *
 *    @Override
 *    public StaggeredGridView getLookupView() {
 *       return lookupView;
 *    }
 *
 *    @Override
 *    public int getCount() {
 *       int count = super.getCount();
 *       if (placeholder.isDisplayed()) {
 *          count++;
 *       }
 *       return count;
 *    }
 *
 *    @Override
 *    public View getView(int position, View convertView, ViewGroup parent) {
 *       if (convertView == null) {
 *          LayoutInflater inflater = (LayoutInflater) getContext()
 *              .getSystemService(android.app.Activity.LAYOUT_INFLATER_SERVICE);
 *          convertView = inflater.inflate(R.layout.fragment_grid_item, null);
 *       }
 *
 *       if (position >= super.getCount()) {
 *          placeholder.bindView(convertView);
 *       } else {
 *          // regular view binding for model getItem(position)
 *       }
 *
 *       return convertView;
 *    }
 *
 *    // ...
 *
 * }
 * 
 * Later in activity or fragment:
 * StaggeredGridView sectionView = (StaggeredGridView) findViewById(R.id.grid);
 * GridAdapter adapter = new GridAdapter(this, getList());
 * adapter.setLookupView(sectionView);
 * sectionView.setAdapter(adapter);
 * 
 * NOTE!
 *
 * It is also a good idea to cleanup when i.e. activity is destroyed.
 * All you need to do is to call GridAdapter.setLookupView(null).
 */
public class GridHeightPlaceholder implements AbsListView.OnScrollListener {
    private AdapterCallbacks adapter;
    private int height = 0, screenWidth = 0;
    private StaggeredGridViewProxy gridView;
    private WeakReference<View> viewRef;

    public GridHeightPlaceholder(AdapterCallbacks adapter) {
        this.adapter = adapter;
    }

    public void listenToScroll() {
        getGridView().setOnScrollListener(this);
    }

    public void stopListeningToScroll() {
        if (gridView != null) {
            gridView.setOnScrollListener(null);
        }
    }

    public void onDetach() {
        if (gridView != null) {
            stopListeningToScroll();
            gridView.onDetach();
            gridView = null;
        }
        if (viewRef != null) {
            viewRef.clear();
        }
    }

    public boolean isDisplayed() {
        return height > 0;
    }

    public void bindView(View view) {
        View content = view.findViewById(R.id.content);
        viewRef = new WeakReference<>(content);
        content.getLayoutParams().height = Math.round(height / 2);
        content.requestLayout();
        content.setAlpha(0);
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {}

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (firstVisibleItem + visibleItemCount >= totalItemCount) {
            StaggeredGridViewProxy gridView = getGridView();
            int[] columnHeights = new int[]{gridView.getColumnBottom(0), gridView.getColumnBottom(1)};
            int columnHeightDiff, newHeight;

            View itemView = getPlaceholderView();
            if (itemView != null) {
                int column = getColumn(itemView);
                columnHeights[column] -= itemView.getHeight();
            }

            columnHeightDiff = Math.abs(columnHeights[0] - columnHeights[1]);

            if (height > columnHeightDiff || columnHeightDiff > gridView.getMeasuredHeight()) {
                newHeight = columnHeightDiff - getGridView().getItemMargin();
                if (newHeight != height) {
                    height = newHeight;
                    adapter.notifyDataSetChanged();
                }
            }
        }
    }

    public int getColumn(View view) {
        int[] coords = new int[2];
        view.getLocationInWindow(coords);
        if (coords[0] >= Math.floor(getScreenWidth(view.getContext()) / 2)) {
            return 1;
        } else {
            return 0;
        }
    }

    private int getScreenWidth(Context context) {
        if (screenWidth <= 0) {
            DisplayMetrics metrics = new DisplayMetrics();
            WindowManager window = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
            window.getDefaultDisplay().getMetrics(metrics);
            screenWidth = metrics.widthPixels;
        }
        return screenWidth;
    }

    private View getPlaceholderView() {
        if (viewRef != null) {
            return viewRef.get();
        } else {
            return null;
        }
    }

    private StaggeredGridViewProxy getGridView() {
        if (gridView == null) {
            gridView = new StaggeredGridViewProxy(adapter.getLookupView());
        }
        return gridView;
    }

    public static interface AdapterCallbacks {
        public void notifyDataSetChanged();
        public StaggeredGridView getLookupView();
    }
}

StaggeredGridViewProxy.java

package no.bstcm.loyaltyapp.core.util;

import android.view.View;
import android.widget.AbsListView;

import com.etsy.android.grid.StaggeredGridView;

import java.lang.ref.WeakReference;
import java.lang.reflect.Array;
import java.lang.reflect.Field;

import no.bstcm.loyaltyapp.core.R;

public class StaggeredGridViewProxy {
    private final WeakReference<StaggeredGridView> targetView;
    private Field columnBottomsField = null;

    public StaggeredGridViewProxy(StaggeredGridView view) {
        this.targetView = new WeakReference<StaggeredGridView>(view);
    }

    public void onDetach() {
        StaggeredGridView view = targetView.get();
        if (view != null) {
            view.setOnScrollListener(null);
            targetView.clear();
        }
    }

    public int getColumnBottom(int column) {
        if (columnBottomsField == null) {
            try {
                columnBottomsField = StaggeredGridView.class.getDeclaredField("mColumnBottoms");
                columnBottomsField.setAccessible(true);
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
                return 0;
            }
        }

        try {
            if (columnBottomsField.getType().isArray()) {
                Object array = columnBottomsField.get(targetView.get());
                return (int) Array.get(array, column);
            }
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        return 0;
    }

    public int getItemMargin() {
        return (int) targetView.get().getResources().getDimension(R.dimen.grid_item_margin);
    }

    public View findViewWithTag(Object tag) {
        return targetView.get().findViewWithTag(tag);
    }

    public void setOnScrollListener(AbsListView.OnScrollListener listener) {
        targetView.get().setOnScrollListener(listener);
    }

    public int getMeasuredHeight() {
        return targetView.get().getMeasuredHeight();
    }
}