Experimental approach to implement expandable RecycleView that works with cursors.

CursorExpandableRecyclerViewAdapter.java

package com.exsoft.musarium.adapter;

/*
 * Copyright (C) 2015 [email protected]
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

import android.database.Cursor;
import android.database.DataSetObserver;

import com.h6ah4i.android.widget.advrecyclerview.utils.AbstractExpandableItemAdapter;
import com.h6ah4i.android.widget.advrecyclerview.utils.AbstractExpandableItemViewHolder;

/**
 * Abstract realization of expandable adapter for RecycleView that works with cursor.
 * Expansion feature itself is base on:
 * https://github.com/h6ah4i/android-advancedrecyclerview
 *
 * The main drawback: in case of changes in list collection itself (ex. implementing some
 * sorting) or background changes in database, code will work unexpectedly. Because it relays on
 * stable data.
 *
 * Created by Dmitriy Gorodnytskiy on 12/19/15.
 */

public abstract class CursorExpandableRecyclerViewAdapter<GVH extends AbstractExpandableItemViewHolder,
        CVH extends AbstractExpandableItemViewHolder> extends AbstractExpandableItemAdapter<GVH, CVH> {

    private Cursor mCursor;

    private boolean mDataValid;

    private int mRowIdColumn;

    private DataSetObserver mDataSetObserver;

    public CursorExpandableRecyclerViewAdapter(Cursor cursor) {
        mCursor = cursor;
        mDataValid = cursor != null;
        mRowIdColumn = mDataValid ? mCursor.getColumnIndex("_id") : -1;
        mDataSetObserver = new NotifyingDataSetObserver();
        if (mCursor != null) {
            mCursor.registerDataSetObserver(mDataSetObserver);
        }
    }

    public Cursor getCursor() {
        return mCursor;
    }

    public abstract Cursor getChildrenCursor(Cursor groupCursor);

    public abstract boolean onCheckGroupExpandable(GVH groupViewHolder, Cursor groupCursor);

    public abstract void onBindGroupViewHolder(GVH groupViewHolder, Cursor groupCursor);

    public abstract void onBindChildViewHolder(CVH childViewHolder, Cursor childCursor);

    @Override
    public final void onBindGroupViewHolder(GVH holder, int groupPosition, int viewType) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(groupPosition)) {
            throw new IllegalStateException("couldn't move cursor to position " + groupPosition);
        }
        onBindGroupViewHolder(holder, mCursor);
    }

    @Override
    public final void onBindChildViewHolder(CVH holder, int groupPosition, int childPosition, int viewType) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(groupPosition)) {
            throw new IllegalStateException("couldn't move cursor to position " + groupPosition);
        }

        Cursor childrenCursor = getChildrenCursor(mCursor);

        if (!childrenCursor.moveToPosition(childPosition)) {
            throw new IllegalStateException("couldn't move children cursor to position " + childPosition);
        }
        onBindChildViewHolder(holder, childrenCursor);
    }

    @Override
    public int getGroupCount() {
        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        }
        return 0;
    }

    @Override
    public int getChildCount(int groupPosition) {
        int count = 0;
        if (mDataValid && mCursor != null && mCursor.moveToPosition(groupPosition)) {
            Cursor c = getChildrenCursor(mCursor);
            count = c.getCount();
            c.close();
        }
        return count;
    }

    @Override
    public long getGroupId(int groupPosition) {
        if (mDataValid && mCursor != null && mCursor.moveToPosition(groupPosition)) {
            return mCursor.getLong(mRowIdColumn);
        }
        return 0;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        long id = 0L;
        if (mDataValid && mCursor != null && mCursor.moveToPosition(groupPosition)) {
            Cursor childrenCursor = getChildrenCursor(mCursor);

            if(childrenCursor.moveToPosition(childPosition)) {
                id = childrenCursor.getLong(mRowIdColumn);
            }
            childrenCursor.close();
        }
        return id;
    }

    @Override
    public final boolean onCheckCanExpandOrCollapseGroup(GVH holder, int groupPosition, int x, int y, boolean expand) {
        return mDataValid && mCursor != null && mCursor.moveToPosition(groupPosition) &&
                onCheckGroupExpandable(holder, mCursor);
    }

    @Override
    public void setHasStableIds(boolean hasStableIds) {
        super.setHasStableIds(true);
    }

    /**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     */
    public void changeCursor(Cursor cursor) {
        Cursor old = swapCursor(cursor);
        if (old != null) {
            old.close();
        }
    }

    /**
     * Swap in a new Cursor, returning the old Cursor.  Unlike
     * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
     * closed.
     */
    public Cursor swapCursor(Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        final Cursor oldCursor = mCursor;
        if (oldCursor != null && mDataSetObserver != null) {
            oldCursor.unregisterDataSetObserver(mDataSetObserver);
        }
        mCursor = newCursor;
        if (mCursor != null) {
            if (mDataSetObserver != null) {
                mCursor.registerDataSetObserver(mDataSetObserver);
            }
            mRowIdColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            notifyDataSetChanged();
        } else {
            mRowIdColumn = -1;
            mDataValid = false;
            notifyDataSetChanged();
            //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
        }
        return oldCursor;
    }

    private class NotifyingDataSetObserver extends DataSetObserver {
        @Override
        public void onChanged() {
            super.onChanged();
            mDataValid = true;
            notifyDataSetChanged();
        }

        @Override
        public void onInvalidated() {
            super.onInvalidated();
            mDataValid = false;
            notifyDataSetChanged();
            //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter
        }
    }
}