Accessing a certain downloaded .sqlite database in external storage from an android app

Question

I am trying to implement an offline map feature in an android WebView-based app:

Using DownloadManager, I download an sqlite database file (of a structure like .mbtiles) from our webserver, which contains blobs of the map tile images (the "offline map") and store it in the android external storage through

public void downloadMap() {
    downloadManager = (DownloadManager) getActivity().getSystemService(Activity.DOWNLOAD_SERVICE);
    DownloadManager.Request r = new DownloadManager.Request(Uri.parse("http://sry.youtoknow.idontwant/map.sqlite"));

    r.setDestinationInExternalFilesDir(getContext(), "map", "map.sqlite");

    downloadManager.enqueue(r);
}

The Download seems to work perfectly well. I register a BroadcastReceiver to receive DownloadManager.ACTION_DOWNLOAD_COMPLETE and store the path to "map.sqlite" using SharedPreferences.

To access the database from JavaScript for using the tile images in the WebView, I intercept XHRequests by checking for a custom fictive schema name customhttp: in the URL:

webView.setWebViewClient(new WebViewClient() {
    public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
        String url = request.getUrl().toString();
        if (!url.startsWith("customhttp:")) {
            return null;
        } else {
            SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getContext());
            SQLiteDatabase db = SQLiteDatabase.openDatabase(preferences.getString("map_uri", Environment.getExternalStorageDirectory().getPath() + "berlin.sqlite"), null, SQLiteDatabase.OPEN_READONLY);
        }
    }
});

My problem is that I seem to implement openDatabase() in a wrong way as I get the following unpleasant error with the corresponding line, but can't figure out why:

E/SQLiteLog(#####):      (14) cannot open file at line ##### of [##########]
E/SQLiteLog(#####):      (14) os_unix.c:#####: (2) open(//file:///storage/emulated/0/Android/data/idontwant.youtoknow.sry/files/map/map.sqlite) - 
E/SQLiteDatabase(#####): Failed to open database 'file:///storage/emulated/0/Android/data/idontwant.youtoknow.sry/files/map/map.sqlite'.
E/SQLiteDatabase(#####): android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14): Could not open database

[...]

The file exists, is not corrupt and its path seems to be correct. I was able to open the file using an SQLite viewing app.

Question: Why does my Code not work; how can I make it work?

I am aware that there exist at least three very similar questions with the above error message here, but they are not that specific, detailed and/or do not exactly fit my needs. I also didn't manage to solve the problem after reading this article:

http://blog.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/.

Thank you very much for your help!

---

UPDATE:

I tried creating a new database using SQLiteDatabase.openOrCreateDatabase() in external storage in order to compare it to the original database. It was not created - instead I surprisingly confronted the same error message (could not open database).

Then I tried again to open a new database, this time in RAM, using SQLiteDatabase.openOrCreateDatabase(":memory:", null) and it did not throw any error.

Thus I begin to think that the problem is some access restriction to external storage or a mistake when addressing external storage rather than the database file itself.

Answer 1

I finally managed to find the mistake, a quite sobering one.

I received DownloadManager.ACTION_DOWNLOAD_COMPLETE and stored the URI to the downloaded database in SharedPreferences for later reference inside the shouldInterceptRequest method using:

...
Cursor c = downloadManager.query(query);
if (c.moveToFirst()) {
    if (c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS)) == DownloadManager.STATUS_SUCCESSFUL) {
        Editor editor = PreferenceManager.getDefaultSharedPreferences(getContext()).edit();
        editor.putString("map_uri", c.getString(c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI)));
        editor.commit();
    }
}
c.close();

In shouldInterceptRequest I then called

SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getContext());
SQLiteDatabase db = SQLiteDatabase.openDatabase(preferences.getString("map_uri", Environment.getExternalStorageDirectory().getPath() + "map.sqlite"), null, SQLiteDatabase.OPEN_READONLY);

and thereby passed the URI to openDatabase, not the Path alone.

I now Uri.parse(preferences.getString("map_uri", ...)).getPath() and everything works. The map loads.

Thank you very much for your help!