See this post:
Android set Album Thumbnail
The bit you need is here:
ContentResolver res = context.getContentResolver();
Uri uri = ContentUris.withAppendedId(sArtworkUri, album_id);
if (uri != null) {
InputStream in = null;
try {
in = res.openInputStream(uri);
return BitmapFactory.decodeStream(in, null, sBitmapOptions);
} catch (FileNotFoundException ex) {
// The album art thumbnail does not actually exist. Maybe the user deleted it, or
// maybe it never existed to begin with.
Bitmap bm = getArtworkFromFile(context, null, album_id);
if (bm != null) {
// Put the newly found artwork in the database.
// Note that this shouldn't be done for the "unknown" album,
// but if this method is called correctly, that won't happen.
// first write it somewhere
String file = Environment.getExternalStorageDirectory()
+ "/albumthumbs/" + String.valueOf(System.currentTimeMillis());
if (ensureFileExists(file)) {
try {
OutputStream outstream = new FileOutputStream(file);
if (bm.getConfig() == null) {
bm = bm.copy(Bitmap.Config.RGB_565, false);
if (bm == null) {
return getDefaultArtwork(context);
}
}
boolean success = bm.compress(Bitmap.CompressFormat.JPEG, 75, outstream);
outstream.close();
if (success) {
ContentValues values = new ContentValues();
values.put("album_id", album_id);
values.put("_data", file);
Uri newuri = res.insert(sArtworkUri, values);
if (newuri == null) {
// Failed to insert in to the database. The most likely
// cause of this is that the item already existed in the
// database, and the most likely cause of that is that
// the album was scanned before, but the user deleted the
// album art from the sd card.
// We can ignore that case here, since the media provider
// will regenerate the album art for those entries when
// it detects this.
success = false;
}
}
if (!success) {
File f = new File(file);
f.delete();
}
} catch (FileNotFoundException e) {
Log.e(TAG, "error creating file", e);
} catch (IOException e) {
Log.e(TAG, "error creating file", e);
}
}
} else {
bm = getDefaultArtwork(context);
}
return bm;
} finally {
try {
if (in != null) {
in.close();
}
} catch (IOException ex) {
}
}
}
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