CursorRecyclerViewAdapter.java

/*
 * Copyright (C) 2016 Evan Halley
 *
 * 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.
 *
 */
package com.emuneee.adapter;

import android.database.Cursor;
import android.database.DataSetObserver;
import android.support.v7.widget.RecyclerView;
import android.text.TextUtils;
import android.util.SparseIntArray;

/**
 * Provides ability to bind a recycler view to a Android database cursor
 * Created by skyfishjy on 10/31/14.
 * Modified by emuneee on 1/5/16.
 */
public abstract class CursorRecyclerViewAdapter<VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<VH> {

    private static final int INSERTED = 1;
    private static final int REMOVED = 2;
    private static final int CHANGED = 3;
    private static final int ALL = -1;

    private final String mComparisonColumn;
    private final DataSetObserver mDataSetObserver;
    private int mRowIdColumn;
    private Cursor mCursor;
    private boolean mDataValid;

    public CursorRecyclerViewAdapter(Cursor cursor) {
        this(cursor, null);
    }

    public CursorRecyclerViewAdapter(Cursor cursor, String comparisonColumn) {
        mCursor = cursor;
        mComparisonColumn = comparisonColumn;
        mDataValid = cursor != null;
        mRowIdColumn = mDataValid ? mCursor.getColumnIndex("_id") : -1;
        mDataSetObserver = new NotifyingDataSetObserver();

        if (mCursor != null) {
            mCursor.registerDataSetObserver(mDataSetObserver);
        }
    }

    public Cursor getCursor() {
        return mCursor;
    }

    @Override
    public int getItemCount() {

        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        }
        return 0;
    }

    @Override
    public long getItemId(int position) {

        if (mDataValid && mCursor != null && mCursor.moveToPosition(position)) {
            return mCursor.getLong(mRowIdColumn);
        }
        return 0;
    }

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

    public abstract void onBindViewHolder(VH viewHolder, Cursor cursor, int position);

    @Override
    public void onBindViewHolder(VH viewHolder, int position) {

        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }

        if (!mCursor.moveToPosition(position)) {
            throw new IllegalStateException("couldn't move cursor to position " + position);
        }
        onBindViewHolder(viewHolder, mCursor, position);
    }

    /**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     */
    public void changeCursor(Cursor cursor) {

        if (mCursor == null) {
            swapCursor(cursor, null);
        } else {
            SparseIntArray changes = null;

            if (cursor != null && cursor != mCursor && !TextUtils.isEmpty(mComparisonColumn)) {
                changes = diffCursors(mCursor, cursor);
            }
            Cursor old = swapCursor(cursor, changes);

            if (old != null) {
                old.close();
            }
        }
    }

    /**
     * Processes two cursors, old/existing cursor and a new cursor, returning a list of indexes who's
     * records were inserted, deleted, or changed
     * @param oldCursor
     * @param newCursor
     * @return
     */
    private SparseIntArray diffCursors(Cursor oldCursor, Cursor newCursor) {

        SparseIntArray changedOrInserted = getChangeOrInsertRecords(oldCursor, newCursor);

        // all records were inserted in new cursor
        if (changedOrInserted.get(ALL) == INSERTED) {
            return changedOrInserted;
        }

        SparseIntArray deleted = getDeletedRecords(oldCursor, newCursor);

        if (deleted.get(ALL) == INSERTED) {
            return deleted;
        }
        SparseIntArray changes = new SparseIntArray(changedOrInserted.size() + deleted.size());

        for (int i = 0; i < changedOrInserted.size(); i++) {
            changes.put(changedOrInserted.keyAt(i), changedOrInserted.valueAt(i));
        }

        for (int i = 0; i < deleted.size(); i++) {
            changes.put(deleted.keyAt(i), deleted.valueAt(i));
        }
        return changes;
    }

    /**
     * Returns a list of indexes of records that were deleted
     * May also return whether or not ALL records were inserted
     * @param oldCursor
     * @param newCursor
     * @return
     */
    private SparseIntArray getDeletedRecords(Cursor oldCursor, Cursor newCursor) {
        SparseIntArray changes = new SparseIntArray();
        int newCursorPosition = newCursor.getPosition();

        if (oldCursor.moveToFirst()) {
            int cursorIndex = 0;

            // loop old cursor
            do {

                if (newCursor.moveToFirst()) {
                    boolean oldRecordFound = false;

                    // loop new cursor
                    do {

                        // we found a record match
                        if (oldCursor.getInt(mRowIdColumn) == newCursor.getInt(mRowIdColumn)) {
                            oldRecordFound = true;
                            break;
                        }
                    } while(newCursor.moveToNext());

                    if (!oldRecordFound) {
                        changes.put(cursorIndex, REMOVED);
                    }
                    cursorIndex++;
                }

            } while (oldCursor.moveToNext());
        }

        // unable to move the old cursor to the first record, all records in new were adde
        else {
            changes.put(ALL, INSERTED);
        }
        newCursor.moveToPosition(newCursorPosition);
        return changes;
    }

    /**
     * Returns an array of indexes who's records were newly inserted or changed
     * Will also return whether or not all the records were inserted or removed
     * @param oldCursor
     * @param newCursor
     * @return
     */
    private SparseIntArray getChangeOrInsertRecords(Cursor oldCursor, Cursor newCursor) {
        SparseIntArray changes = new SparseIntArray();
        int newCursorPosition = newCursor.getPosition();

        if (newCursor.moveToFirst()) {
            int columnIndex = oldCursor.getColumnIndex(mComparisonColumn);
            int cursorIndex = 0;

            // loop
            do {

                if (oldCursor.moveToFirst()) {
                    boolean newRecordFound = false;

                    // loop
                    do {

                        // we found a record match
                        if (oldCursor.getInt(mRowIdColumn) == newCursor.getInt(mRowIdColumn)) {
                            newRecordFound = true;

                            // values are different, this record has changed
                            if (!oldCursor.getString(columnIndex).contentEquals(newCursor.getString(columnIndex))) {
                                changes.put(cursorIndex, CHANGED);
                            }
                            break;
                        }
                    } while (oldCursor.moveToNext());

                    // new record not found in old cursor, it was newly inserted
                    if (!newRecordFound) {
                        changes.put(cursorIndex, INSERTED);
                    }
                    cursorIndex++;
                }

                // unable to move the new cursor, all records in new are inserted
                else {
                    changes.put(ALL, INSERTED);
                    break;
                }
            } while (newCursor.moveToNext());
        }

        // unable to move new cursor to first
        else {
            changes.put(ALL, REMOVED);
        }
        newCursor.moveToPosition(newCursorPosition);
        return changes;
    }

    /**
     *
     * @param newCursor
     * @param changes
     * @return
     */
    private Cursor swapCursor(Cursor newCursor, SparseIntArray changes) {

        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;
        } else {
            mRowIdColumn = -1;
            mDataValid = false;
        }

        if (changes != null) {
            // process changes
            if (changes.get(ALL) == INSERTED) {
                notifyItemRangeInserted(0, newCursor.getCount());
            } else if (changes.get(ALL) == REMOVED) {
                notifyItemRangeRemoved(0, newCursor.getCount());
            } else {

                for (int i = 0; i < changes.size(); i++) {

                    switch (changes.valueAt(i)) {
                        case CHANGED:
                            notifyItemChanged(changes.keyAt(i));
                            break;
                        case INSERTED:
                            notifyItemInserted(changes.keyAt(i));
                            break;
                        case REMOVED:
                            notifyItemRemoved(changes.keyAt(i));
                            break;
                    }
                }
            }
        } else if (mCursor != null) {
            notifyItemRangeInserted(0, mCursor.getCount());
        }
        return oldCursor;
    }

    private class NotifyingDataSetObserver extends DataSetObserver {

        @Override
        public void onChanged() {
            super.onChanged();
            mDataValid = true;
        }

        @Override
        public void onInvalidated() {
            super.onInvalidated();
            mDataValid = false;
        }
    }
}

There seem to be an issue at

else if (changes.get(ALL) == REMOVED) { notifyItemRangeRemoved(0, newCursor.getCount()); }

It crashes with Inconsistency detected. Invalid view holder adapter positionViewHolder when there is only 1 record

I have manged to avoid it by using oldCursor.getCount() instead of newCursor.getCount()
But, it does not sound allright to me.

I use Swipe delete from https://github.com/HoneyNeutrons/RecyclerViewUndoSwipe/blob/master/app/src/main/java/com/honeyneutrons/undoswipe/helper/SimpleItemTouchHelperCallback.java and there is always a red row flashing at the bottom

Any thoughts?

Seems good solution to me....will try it tonight. Was looking for something like this only else have to implement myself. Good source to start with. Will be looking to optimize it.
And that date advice was really helpful. Thanks winks