通过DDMS，我们在/data/data/com.android.providers.media下找到数据库文件　　

打开external.db文件进一步查看：在media表格下，可以看到文件路径(_data)和Uri的标示ID(_id)的对应关系。　　

二、URI与文件相互转换

1.从URI获得文件路径

string myImageUrl = "content://media/external/images/media/***";
Uri uri = Uri.parse(myImageUrl);


String[] proj = { MediaStore.Images.Media.DATA };
Cursor actualimagecursor = this.ctx.managedQuery(uri,proj,null,null,null);
int actual_image_column_index = actualimagecursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
actualimagecursor.moveToFirst();


String img_path = actualimagecursor.getString(actual_image_column_index);
File file = new File(img_path);
Uri fileUri = Uri.fromFile(file);

2.由文件路径得到URI

Uri mUri = Uri.parse("content://media/external/images/media");
Uri mImageUri = null;

Cursor cursor = managedQuery(
MediaStore.Images.Media.EXTERNAL_CONTENT_URI, null, null,
null, MediaStore.Images.Media.DEFAULT_SORT_ORDER);
cursor.moveToFirst();

while (!cursor.isAfterLast()) {
String data = cursor.getString(cursor
.getColumnIndex(MediaStore.MediaColumns.DATA));
if (picPath.equals(data)) {
int ringtoneID = cursor.getInt(cursor
.getColumnIndex(MediaStore.MediaColumns._ID));
mImageUri = Uri.withAppendedPath(mUri, ""
+ ringtoneID);
break;
}
cursor.moveToNext();
}