TileContentProvider.java

/*
 * Needs a tile layer, something like (for Leaflet) ..
 * 
 * var tl = L.tileLayer("content://com.pahasapatrails.m.tiles/{style}/{z}/{x}/{y}.png",
 *     { style: "XXX", minZoom: 9, maxZoom: 13, tms: true });
 * map.addLayer(tl);
 *
 * 
 * Also needs a provider entry under the application tag in the Android
 * Manifest, something like the following ..
 * 
 * <provider android:name="com.pahasapatrails.m.TileContentProvider"
 *     android:authorities="com.pahasapatrails.m.tiles" />
 *
 */

package com.pahasapatrails.m;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.ParcelFileDescriptor;
import android.util.Log;

public class TileContentProvider extends ContentProvider {

//    private String databaseList[] = null;
//    private SQLiteDatabase databases[];
    
    private SQLiteDatabase handle;
    private String query = "SELECT tile_data FROM images INNER JOIN map ON " +
        "images.tile_id = map.tile_id WHERE zoom_level = ? " +
        " AND tile_column = ? AND tile_row = ?";
    
    /*
     * onCreate is called when the application manifest is read at startup time.
     * Do one-time initialization magic here, the provider will keep running
     * so we only have to open each database once and cache the handle.
     */
    @Override
    public boolean onCreate()
    {
        /*
         * Delete the cache, just in case anything stuck around somehow
         */
        File cacheDir = this.getContext().getCacheDir();
        String[] children = cacheDir.list();
        for (int i = 0; i < children.length; i++) {
            new File(cacheDir, children[i]).delete();
        }

        /*
         * Setup the database connection(s)
         * 
         * XXX: Hardcoded database filename
         */
        String dbname = "PahaSapaTrailscomMobile9-13.mbtiles";
        File dbfile = this.getContext().getDatabasePath(dbname);
        handle = SQLiteDatabase.openOrCreateDatabase(dbfile, null);
        
        return (true);
    }

    /*
     * Query the MBTiles DB and return content-type
     * 
     * XXX: Does this ever even get called by a webview?
     */
    @Override
    public String getType(Uri uri)
    {
        Log.e("error", "TileContentProvider: getType: " + uri);
        return ("image/png");
    }   

    /*
     * If only concerned with HONEYCOMB and later then openFile could simply
     * use simpleQueryForBlobFileDescriptor and return that descriptor --
     * at least ostensibly, untested.
     */
    @Override
    public ParcelFileDescriptor openFile(Uri uri, String mode)
            throws FileNotFoundException
    {
        if (mode != "r")
            throw new FileNotFoundException("mode can only be of type read-only");

        /*
         * Parse uri, path looks like /scheme/zoom/x/y.png
         * 
         * XXX: Assumes png
         */
        String path[] = uri.getPath().split("/");
        String params[] = { path[2], path[3], path[4].replace(".png", "") };
        String outfilename = params[0] + "-" + params[1] + "-" + params[2] + ".png";

        try {
            File file = new File(this.getContext().getCacheDir(), outfilename);

            Cursor cursor = handle.rawQuery(query, params);
            if (!cursor.moveToFirst())
                throw new FileNotFoundException("No results from query");

            BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
            bos.write(cursor.getBlob(0));
            cursor.close();
            ParcelFileDescriptor ret = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
            bos.close();
            
            /*
             * Unlink underneath? Actual file will *poof* once the
             * ParcelFileDescriptor we are returning gets closed.
             */
            file.delete();
            
            handle.setTransactionSuccessful();
            return (ret);
        } catch (IOException e) {
            e.printStackTrace();
            /* Return static error image instead? */
            throw new FileNotFoundException("Error setting up tile");
        }
    }

    
    /*
     * query, delete, insert and update operations are specifically not supported,
     * the application must download the mbtiles database files and place them
     * in the expected data directory.
     */

    @Override
    public Cursor query(Uri uri, String[] arg1, String arg2, String[] arg3, String arg4)
    {
        throw new UnsupportedOperationException("Not supported by this provider");
    }

    @Override
    public int delete(Uri uri, String arg1, String[] arg2)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public Uri insert(Uri uri, ContentValues arg1)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public int update(Uri uri, ContentValues arg1, String arg2, String[] arg3)
    {
        throw new UnsupportedOperationException();
    }
}

Hi,

I didn't know about gist. I just tried your code and it was throwing an exception. I found that the

handle.setTransactionSuccessful();

was the cause, so I added some validation to it :

if (handle.inTransaction())
{
    handle.setTransactionSuccessful();
}

Here's the end result in a fork : https://gist.github.com/adube/5041097

Thanks for sharing your code.