Query two and more song at one time using the function "addFilterPredicate" by MPMediaItemPropertyPersistentID

Question

My app loads a music playlist automatically when it starts up. In order to do this, I store the song IDs MPMediaItemPropertyPersistentID to a database, and load the songs when the app is starting up next time. The main code is the following:

MPMediaQuery *MPMediaSongQuery = [MPMediaQuery songsQuery];

MPMediaPropertyPredicate *iPodMusicSongPredicateiPodMusicSongPredicate = [MPMediaPropertyPredicate 
                                  predicateWithValue:[NSNumber numberWithUnsignedLongLong: songID] 
                                  forProperty:MPMediaItemPropertyPersistentID     
                                  comparisonType:MPMediaPredicateComparisonEqualTo];

[MPMediaSongQuery addFilterPredicate:iPodMusicSongPredicate];
NSArray *collections = MPMediaSongQuery.collections;

The code loads song one by one. My question is: is there any way to query two or more songs by MPMediaItemPropertyPersistentID at one time when using the function addFilterPredicate:? Thanks.

Answer 1

If you use more than one addFilterPredicate they are combined with a logical AND. So you canm only reduce the results of the first query, but not extend it. As a consequence you are not allowed to use several addFilterPredicates for the same property. In fact the result is undefined and most likely will end up in an empty collection. What you are looking for is a combination of the same property with a logical OR. You can achieve this like depicted in the following pseudo-code:

MPMediaQuery *MPMediaSongQuery = [MPMediaQuery songsQuery];

NSMutableArray *collections = [[NSMutableArray alloc] initWithCapacity:1];

for (int i=0; i < songIDCount; i++) {

   MPMediaPropertyPredicate *iPodMusicSongPredicateiPodMusicSongPredicate = [MPMediaPropertyPredicate 
                                  predicateWithValue:[NSNumber numberWithUnsignedLongLong: songID[i]] 
                                  forProperty:MPMediaItemPropertyPersistentID     
                                  comparisonType:MPMediaPredicateComparisonEqualTo];

   [MPMediaSongQuery addFilterPredicate:iPodMusicSongPredicate];

   [collections addObjectsFromArray:MPMediaSongQuery.collections];

   [MPMediaSongQuery removeFilterPredicate:iPodMusicSongPredicate];

}

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