Swift 再生中の曲の「年」の取り出し方

 テスト環境

• MacOS Sierra 10.12.6
• Xcode 9.2 Build version 9C40b
• Apple Swift version 4.0.3 (swiftlang-900.0.74.1 clang-900.0.39.2)

 ソース

iTunesでは年が表示されているのに、
releaseDateとvalue(forProperty: MPMediaItemPropertyReleaseDate)で
nilを返すケースがありますね。Open Radar では不具合とされています。
そのケースでも、value(forProperty: "year")で値が取得できました。そちらも利用してみてください。

import AVFoundation
import MediaPlayer
import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let albumsQuery = MPMediaQuery.albums()
        guard let albums: [MPMediaItemCollection] = albumsQuery.collections else {
            print("error")
            return
        }

        for album in albums {

            let title = album.representativeItem?.albumTitle ?? ""
            let artist = album.representativeItem?.albumArtist ?? ""
            let releaseDate = album.representativeItem?.releaseDate
            let propertyReleaseDate = album.representativeItem?.value(forProperty: MPMediaItemPropertyReleaseDate)
            let year = album.representativeItem?.value(forProperty: "year")

            print("title: \(title)")
            print("artist: \(artist)")
            print("releaseDate: \(releaseDate)")
            print("propertyReleaseDate: \(propertyReleaseDate)")
            print("year: \(year)\n")

            for single in (album.items) {

                let singleTitle = single.value(forProperty: MPMediaItemPropertyTitle) ?? ""
                let singleArtist = single.value(forProperty: MPMediaItemPropertyArtist) ?? ""
                let singleReleaseDate = single.releaseDate
                let singlePropertyReleaseDate = single.value(forProperty: MPMediaItemPropertyReleaseDate)
                let singleYear = single.value(forProperty: "year")

                print("singleTitle: \(singleTitle)")
                print("singleArtist: \(singleArtist)")
                print("singleReleaseDate: \(singleReleaseDate)")
                print("singlePropertyReleaseDate: \(singlePropertyReleaseDate)")
                print("singleYear: \(singleYear)\n")
            }
        }

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

 サンプル

title: GOLDEN☆BEST 村下孝蔵ベスト・セレクト・ソングズ
artist: 村下孝蔵
releaseDate: nil
propertyReleaseDate: nil
year: Optional(2013)

singleTitle: 初恋
singleArtist: 村下孝蔵
singleReleaseDate: nil
singlePropertyReleaseDate: nil
singleYear: Optional(2013)

---略---

title: Songs of Innocence
artist: U2
releaseDate: Optional(2014-09-09 07:00:00 +0000)
propertyReleaseDate: Optional(2014-09-09 07:00:00 +0000)
year: Optional(2014)

singleTitle: The Miracle (Of Joey Ramone)
singleArtist: U2
singleReleaseDate: Optional(2014-09-09 07:00:00 +0000)
singlePropertyReleaseDate: Optional(2014-09-09 07:00:00 +0000)
singleYear: Optional(2014)

releaseDateとvalue(forProperty: "year")が一致しないケースもありました。
iTunesで表示されているのは1981です。

title: グレイテスト・ヒッツ
artist: クイーン
releaseDate: Optional(1981-10-26 08:00:00 +0000)
propertyReleaseDate: Optional(1981-10-26 08:00:00 +0000)
year: Optional(2011)

singleTitle: Bohemian Rhapsody (2011 Remaster)
singleArtist: クイーン
singleReleaseDate: Optional(1981-10-26 08:00:00 +0000)
singlePropertyReleaseDate: Optional(1981-10-26 08:00:00 +0000)
singleYear: Optional(2011)

 参考

ios - Release Date of MPMediaItem returning Nil (Swift 4) - Stack Overflow
rdar://21765993: MPMediaItemPropertyReleaseDate returns nil although Music app shows year