How can I refresh MediaStore on Android?

Here is an easy to use 'single file based' solution:

Adding a file:

Whenever you add a file, inform MediaStore's Content Provider using:

sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.fromFile(newMediaFile)));

Deleting a file:

Similarly, when you delete a file, inform MediaStore's Content Provider using:

getContentResolver().delete(uri, null, null)  // (Credit goes to [DDSports][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/

UPDATE 2: Tuesday, April 9, 2013

I've gotten a lot of traffic to my blog from this post, and a huge number of emails from people thanking me for it. Glad it helped out! Any potential users should know that my crappy app currently crashes as soon as you run it, but actually does what it's supposed to do! I've always intended to go back and fix this crashing behaviour and put it on the market, hopefully 2013 will be the year I do that.