CursorRecyclerAdapter.java

package jeevuz.recyclerview;

import android.database.ContentObserver;
import android.database.Cursor;
import android.database.DataSetObserver;
import android.os.Handler;
import android.support.v7.widget.RecyclerView;
import android.widget.Filter;
import android.widget.FilterQueryProvider;
import android.widget.Filterable;

/**
 * Provide a {@link android.support.v7.widget.RecyclerView.Adapter} implementation with cursor
 * support.
 * <p/>
 * Child classes only need to implement {@link #onCreateViewHolder(android.view.ViewGroup, int)} and
 * {@link #onBindViewHolderCursor(android.support.v7.widget.RecyclerView.ViewHolder, android.database.Cursor)}.
 * <p/>
 * This class does not implement deprecated fields and methods from CursorAdapter! Incidentally,
 * only {@link android.widget.CursorAdapter#FLAG_REGISTER_CONTENT_OBSERVER} is available, so the
 * flag is implied, and only the Adapter behavior using this flag has been ported.
 *
 * @author Shywim, edited by Jeevuz (vasili.chyrvon@gmail.com)
 * @see <a href=https://gist.github.com/Shywim/127f207e7248fe48400b>Shyvim's gist</a>
 * @see android.widget.CursorAdapter
 * @see android.support.v7.widget.RecyclerView.Adapter
 * @see android.widget.Filterable
 */
public abstract class CursorRecyclerAdapter<VH extends android.support.v7.widget.RecyclerView.ViewHolder>
        extends RecyclerView.Adapter<VH> implements Filterable, CursorFilter.CursorFilterClient {
    private boolean mDataValid;
    private int mRowIDColumn;
    private Cursor mCursor;
    private ChangeObserver mChangeObserver;
    private DataSetObserver mDataSetObserver;
    private CursorFilter mCursorFilter;
    private FilterQueryProvider mFilterQueryProvider;

    public CursorRecyclerAdapter(Cursor cursor) {
        init(cursor);
    }

    void init(Cursor c) {
        boolean cursorPresent = c != null;
        mCursor = c;
        mDataValid = cursorPresent;
        mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1;

        mChangeObserver = new ChangeObserver();
        mDataSetObserver = new MyDataSetObserver();

        if (cursorPresent) {
            if (mChangeObserver != null) c.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver);
        }
    }

    /**
     * This method will move the Cursor to the correct position and call
     * {@link #onBindViewHolderCursor(android.support.v7.widget.RecyclerView.ViewHolder,
     * android.database.Cursor)}.
     *
     * @param holder {@inheritDoc}
     * @param i      {@inheritDoc}
     */
    @Override
    public void onBindViewHolder(VH holder, int i) {
        if (!mDataValid) {
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(i)) {
            throw new IllegalStateException("couldn't move cursor to position " + i);
        }
        onBindViewHolderCursor(holder, mCursor);
    }

    /**
     * See {@link android.widget.CursorAdapter#bindView(android.view.View, android.content.Context,
     * android.database.Cursor)},
     * {@link #onBindViewHolder(android.support.v7.widget.RecyclerView.ViewHolder, int)}
     *
     * @param holder View holder.
     * @param cursor The cursor from which to get the data. The cursor is already
     *               moved to the correct position.
     */
    public abstract void onBindViewHolderCursor(VH holder, Cursor cursor);

    @Override
    public int getItemCount() {
        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        } else {
            return 0;
        }
    }
    
    /**
     * This is not required by RecyclerView.Adaper, but is useful sometime
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        if (mDataValid && mCursor != null) {
            mCursor.moveToPosition(position);
            return mCursor;
        } else {
            return null;
        }
    }

    /**
     * Get the row id associated with the specified position in the list. If {@link #hasStableIds()}
     * would return false, Cursor is null or empty, or data is not valid, this method would return
     * {@link android.support.v7.widget.RecyclerView#NO_ID}
     *
     * @param position The position of the item within the adapter's data set whose row id we want.
     * @return id The id of the item at the specified position or {@link android.support.v7.widget.RecyclerView#NO_ID}
     * @see android.widget.ListAdapter#getItemId(int)
     * @see android.support.v7.widget.RecyclerView.Adapter#getItemId(int)
     */
    @Override
    public long getItemId(int position) {
        if (hasStableIds() && mDataValid && mCursor != null && mCursor.moveToPosition(position)) {
            return mCursor.getLong(mRowIDColumn);
        } else {
            return RecyclerView.NO_ID;
        }
    }

    public Cursor getCursor() {
        return mCursor;
    }

    /**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     *
     * @param cursor The new cursor to be used
     */
    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.
     *
     * @param newCursor The new cursor to be used.
     * @return Returns the previously set Cursor, or null if there wasa not one.
     * If the given new Cursor is the same instance is the previously set
     * Cursor, null is also returned.
     */
    public Cursor swapCursor(Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        Cursor oldCursor = mCursor;
        int oldItemCount = getItemCount();
        if (oldCursor != null) {
            if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver);
            if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver);
        }
        mCursor = newCursor;
        if (newCursor != null) {
            if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver);
            if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver);
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            // notify the observers about the new cursor
            notifyDataSetChanged();
        } else {
            mRowIDColumn = -1;
            mDataValid = false;
            // notify the observers about the lack of a data set
            notifyItemRangeRemoved(0, oldItemCount);
        }
        return oldCursor;
    }

    /**
     * <p>Converts the cursor into a CharSequence. Subclasses should override this
     * method to convert their results. The default implementation returns an
     * empty String for null values or the default String representation of
     * the value.</p>
     *
     * @param cursor the cursor to convert to a CharSequence
     * @return a CharSequence representing the value
     */
    public CharSequence convertToString(Cursor cursor) {
        return cursor == null ? "" : cursor.toString();
    }

    /**
     * Runs a query with the specified constraint. This query is requested
     * by the filter attached to this adapter.
     * <p/>
     * The query is provided by a
     * {@link android.widget.FilterQueryProvider}.
     * If no provider is specified, the current cursor is not filtered and returned.
     * <p/>
     * After this method returns the resulting cursor is passed to {@link #changeCursor(Cursor)}
     * and the previous cursor is closed.
     * <p/>
     * This method is always executed on a background thread, not on the
     * application's main thread (or UI thread.)
     * <p/>
     * Contract: when constraint is null or empty, the original results,
     * prior to any filtering, must be returned.
     *
     * @param constraint the constraint with which the query must be filtered
     * @return a Cursor representing the results of the new query
     * @see #getFilter()
     * @see #getFilterQueryProvider()
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     */
    public Cursor runQueryOnBackgroundThread(CharSequence constraint) {
        if (mFilterQueryProvider != null) {
            return mFilterQueryProvider.runQuery(constraint);
        }

        return mCursor;
    }

    public Filter getFilter() {
        if (mCursorFilter == null) {
            mCursorFilter = new CursorFilter(this);
        }
        return mCursorFilter;
    }

    /**
     * Returns the query filter provider used for filtering. When the
     * provider is null, no filtering occurs.
     *
     * @return the current filter query provider or null if it does not exist
     * @see #setFilterQueryProvider(android.widget.FilterQueryProvider)
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public FilterQueryProvider getFilterQueryProvider() {
        return mFilterQueryProvider;
    }

    /**
     * Sets the query filter provider used to filter the current Cursor.
     * The provider's
     * {@link android.widget.FilterQueryProvider#runQuery(CharSequence)}
     * method is invoked when filtering is requested by a client of
     * this adapter.
     *
     * @param filterQueryProvider the filter query provider or null to remove it
     * @see #getFilterQueryProvider()
     * @see #runQueryOnBackgroundThread(CharSequence)
     */
    public void setFilterQueryProvider(FilterQueryProvider filterQueryProvider) {
        mFilterQueryProvider = filterQueryProvider;
    }

    /**
     * Called when the {@link ContentObserver} on the cursor receives a change notification.
     * Can be implemented by sub-class.
     *
     * @see ContentObserver#onChange(boolean)
     */
    protected void onContentChanged() {

    }

    private class ChangeObserver extends ContentObserver {
        public ChangeObserver() {
            super(new Handler());
        }

        @Override
        public boolean deliverSelfNotifications() {
            return true;
        }

        @Override
        public void onChange(boolean selfChange) {
            onContentChanged();
        }
    }

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

        @Override
        public void onInvalidated() {
            int itemCount = getItemCount();
            mDataValid = false;
            // data vas invalidated and no longer available
            notifyItemRangeRemoved(0, itemCount);
        }
    }

    /**
     * <p>The CursorFilter delegates most of the work to the CursorAdapter.
     * Subclasses should override these delegate methods to run the queries
     * and convert the results into String that can be used by auto-completion
     * widgets.</p>
     */

}

class CursorFilter extends Filter {

    CursorFilterClient mClient;

    interface CursorFilterClient {
        CharSequence convertToString(Cursor cursor);

        Cursor runQueryOnBackgroundThread(CharSequence constraint);

        Cursor getCursor();

        void changeCursor(Cursor cursor);
    }

    CursorFilter(CursorFilterClient client) {
        mClient = client;
    }

    @Override
    public CharSequence convertResultToString(Object resultValue) {
        return mClient.convertToString((Cursor) resultValue);
    }

    @Override
    protected FilterResults performFiltering(CharSequence constraint) {
        Cursor cursor = mClient.runQueryOnBackgroundThread(constraint);

        FilterResults results = new FilterResults();
        if (cursor != null) {
            results.count = cursor.getCount();
            results.values = cursor;
        } else {
            results.count = 0;
            results.values = null;
        }
        return results;
    }

    @Override
    protected void publishResults(CharSequence constraint, FilterResults results) {
        Cursor oldCursor = mClient.getCursor();

        if (results.values != null && results.values != oldCursor) {
            mClient.changeCursor((Cursor) results.values);
        }
    }
}

I've modified a few places in code:

• getItemId() method to return NO_ID as in description of this method from RecyclerView.Adapter.
• I got the itemCount before changing the mCursor to null or sed mDataValid to false. This is to make call for notifyItemRangeRemoved(0, itemCount) with meaningful results.

Added getItem() method as in CursorAdapter