How can I refresh MediaStore on Android?

Question

This started out as a general user question on Android forums. However it's become, by necessity, a programming question. Here's my problem.

Android has a service - MediaScanner - which runs in the background any time (I believe) the SD card is un-mounted and re-mounted. This service collects data on all the media files on the card, and provides a SQLite DB which can be queried by music applications. Most music applications use this service as it saves on battery-drain associated with scanning the SD card.

Since I started using android, I've consistently had a problem whereby M3U playlists synchronised to the device remain in this SQLite DB even after being deleted from the SD Card. It's gotten to the point where I now have a collection of about 40 playlists showing up in any music app I use, despite there only being around 10 m3u files on the card. The remaining playlists do not play, and are empty. I can remove them manually by deleting them from the music app, but I'm sick of doing this. There has to be a better way to remove these ghost playlists.

There are two apps on the Android Market - SDRescan and Music Scanner, which supposedly do exactly this but neither of them work.

I set about writing my own app to refresh or delete the MediaStore database and start from scratch, but I'm not getting very far. I've got an android app which runs the following code :

sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, 
        Uri.parse("file://" + Environment.getExternalStorageDirectory()))); 

I've found a few examples of this code online as a way to scan the SD Card but I'm not having any luck with it whatsoever. Any tips?

FULL CODE:

package com.roryok.MediaRescan;

import android.app.Activity;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;

public class MediaRescan extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, 
                Uri.parse("file://" + Environment.getExternalStorageDirectory()))); 
        setContentView(R.layout.main);
    }

    //Rescan the sdcard after copy the file
    private void rescanSdcard() throws Exception{     
      Intent scanIntent = new Intent(Intent.ACTION_MEDIA_MOUNTED, 
                Uri.parse("file://" + Environment.getExternalStorageDirectory()));   
      IntentFilter intentFilter = new IntentFilter(Intent.ACTION_MEDIA_SCANNER_STARTED);
      intentFilter.addDataScheme("file");     
      sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, 
                Uri.parse("file://" + Environment.getExternalStorageDirectory())));    
    }
}

Answer 1

Ok, I've done it.

Rather than rescan the card, the app iterates through all the playlists in mediastore and checks the length of the _data field. I discovered that for all the lists with no associated M3U file, this field was always empty. Then it was just a case of finding the source code for the original android music app, finding the delete method and using that to delete any playlists with a length of 0. I've renamed the app PlaylistPurge (since it doesn't 'rescan' anymore) and am posting the code below.

I'll probably also publish this somewhere, either on the Market or on my own site, http://roryok.com

package com.roryok.PlaylistPurge;

import java.util.ArrayList;
import java.util.List;

import android.app.ListActivity;
import android.content.ContentUris;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;

public class PlaylistPurge extends ListActivity {

    private List<String> list = new ArrayList<String>();
    private final String [] STAR= {"*"};

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ListAdapter adapter = createAdapter();
        setListAdapter(adapter);
    }

    /**
     * Creates and returns a list adapter for the current list activity
     * @return
     */
    protected ListAdapter createAdapter()
    {
        // return play-lists
        Uri playlist_uri= MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI;    
        Cursor cursor= managedQuery(playlist_uri, STAR, null,null,null);
        cursor.moveToFirst();
        for(int r= 0; r<cursor.getCount(); r++, cursor.moveToNext()){
            int i = cursor.getInt(0);
            int l = cursor.getString(1).length();
            if(l>0){
                // keep any playlists with a valid data field, and let me know
                list.add("Keeping : " + cursor.getString(2) + " : id(" + i + ")");
            }else{
                // delete any play-lists with a data length of '0'
                Uri uri = ContentUris.withAppendedId(MediaStore.Audio.Playlists.EXTERNAL_CONTENT_URI, i);
                getContentResolver().delete(uri, null, null);
                list.add("Deleted : " + cursor.getString(2) + " : id(" + i + ")");
            }
        }       
        cursor.close();
        // publish list of retained / deleted playlists
        ListAdapter adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);

        return adapter;
    }
}

UPDATE:

Here's a link to a post on my blog about the app http://roryok.com/blog/index.php/2010/07/23/clearing-out-deleted-playlists-in-android/