CODEWITHSUNDEEP
iosswiftmpmediaquery
Tom Ax
Tom Ax

Reputation: 576

iOS Query via Album MPMediaEntityPersistentID sometimes brings back no songs

I'm writing an app that plays music using Apple's built in MediaPlayer library. I store an array of albums and an array of Ids, and then when one is selected I search for an album using the id. For some reason, some of the albums can't find any songs despite having an id associated with them. It is the same albums each time that won't work, and there seems to be no pattern to this.

I use the following code to store the names and ids into two arrays

let query = MPMediaQuery.albumsQuery()
let mediaCollection = MPMediaItemCollection(items: query.items!)

for album in mediaCollection.items {
            albumTitleArray.append(album.albumTitle!)
            albumIdArray.append(album.albumPersistentID)
        }

When one is selected, I then pass the id to the queryMedia method

func queryMedia(identifier:MPMediaEntityPersistentID) -> MPMediaItemCollection {

    let predicateId = MPMediaPropertyPredicate(value: String(identifier), forProperty: MPMediaItemPropertyAlbumPersistentID, comparisonType:MPMediaPredicateComparison.EqualTo)

    let query = MPMediaQuery.init()
    query.addFilterPredicate(predicateId)

    let collection = MPMediaItemCollection(items: query.items!)

    return collection;
}

Any help in resolving this would be appreciated!

Upvotes: 1

Views: 1367

Answers (2)

David Kaufman
David Kaufman

Reputation: 121

I am using XCode 13.1 and iOS 14.8 at the moment and this is still an issue.

I need to wrap the persistentId with NSNumber(value: persistentId) for this to work correctly.

But I also discovered that if I first created a query using MPMediaQuery.songs() then I did not have to use NSNumber()

func LoadMediaLibraryTrackData(_ track: inout AudioZoomTrack, _ persistentId:MPMediaEntityPersistentID) {
        
  /// Works
  let trackFilter = MPMediaPropertyPredicate(value: NSNumber(value: persistentId), forProperty: MPMediaItemPropertyPersistentID)
  let query = MPMediaQuery(filterPredicates: [trackFilter])

  /// Fails
  let trackFilter = MPMediaPropertyPredicate(value: persistentId, forProperty: MPMediaItemPropertyPersistentID)
  let query = MPMediaQuery(filterPredicates: [trackFilter])

  /// Works
  let query = MPMediaQuery.songs()
  let trackFilter = MPMediaPropertyPredicate(value: persistentId, forProperty: MPMediaItemPropertyPersistentID)     
  query.addFilterPredicate(trackFilter)

  ...
}

Upvotes: 0

Tom Ax
Tom Ax

Reputation: 576

There must have been some characters being malformed, or a comparison error in the query caused by the conversion from MPMediaEntityPersistentID to String.

I've changed the code to instead convert to a NSNumber and the query now finds all albums correctly.

change this part in code example above

String(identifier)

to

NSNumber(unsignedLongLong: identifier)

so it looks like this

func queryMedia(identifier:MPMediaEntityPersistentID) -> MPMediaItemCollection {

let predicateId = MPMediaPropertyPredicate(value: NSNumber(unsignedLongLong: identifier), forProperty: MPMediaItemPropertyAlbumPersistentID, comparisonType:MPMediaPredicateComparison.EqualTo)

let query = MPMediaQuery.init()
query.addFilterPredicate(predicateId)

let collection = MPMediaItemCollection(items: query.items!)

return collection;
}

Upvotes: 4

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