musickit

# MusicKit

Search the Apple Music catalog, manage playback with `ApplicationMusicPlayer`,
check subscriptions, and publish Now Playing metadata via `MPNowPlayingInfoCenter`
and `MPRemoteCommandCenter`. Targets Swift 6.3 / iOS 26+.

## Contents

- [Setup](#setup)
- [Authorization](#authorization)
- [Catalog Search](#catalog-search)
- [Subscription Checks](#subscription-checks)
- [Playback with ApplicationMusicPlayer](#playback-with-applicationmusicplayer)
- [Queue Management](#queue-management)
- [Now Playing Info](#now-playing-info)
- [Remote Command Center](#remote-command-center)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Setup

### Project Configuration

1. Enable the **MusicKit App Service** for the app's explicit bundle ID in the Apple Developer portal so MusicKit can generate developer tokens automatically.
2. Add `NSAppleMusicUsageDescription` to Info.plist explaining why the app accesses the user's media library.
3. For background playback, add the `audio` background mode to `UIBackgroundModes`.

### Imports

```swift
import MusicKit       // Catalog, auth, playback
import MediaPlayer    // MPRemoteCommandCenter, MPNowPlayingInfoCenter
```

## Authorization

Request permission before accessing the user's music data or playing Apple Music
content. `request()` presents Apple's consent dialog when necessary; use
`currentStatus` to read the current setting without prompting.

```swift
func requestMusicAccess() async -> MusicAuthorization.Status {
    let status = await MusicAuthorization.request()
    switch status {
    case .authorized:
        // Full access to MusicKit APIs
        break
    case .denied, .restricted:
        // Show guidance to enable in Settings
        break
    case .notDetermined:
        break
    @unknown default:
        break
    }
    return status
}

// Check current status without prompting
let current = MusicAuthorization.currentStatus
```

## Catalog Search

Use `MusicCatalogSearchRequest` to search the Apple Music catalog. Catalog lookup
can fetch Apple Music resources, but playback of subscription catalog content
must still be gated on `MusicSubscription.current.canPlayCatalogContent`.

```swift
func searchCatalog(term: String) async throws -> MusicItemCollection<Song> {
    var request = MusicCatalogSearchRequest(term: term, types: [Song.self])
    request.limit = 25

    let response = try await request.response()
    return response.songs
}
```

### Displaying Results

```swift
for song in songs {
    print("\(song.title) by \(song.artistName)")
    if let artwork = song.artwork {
        let url = artwork.url(width: 300, height: 300)
        // Load artwork from url
    }
}
```

## Subscription Checks

Check whether the user has an active Apple Music subscription before offering playback features.

```swift
func checkSubscription() async throws -> Bool {
    let subscription = try await MusicSubscription.current
    return subscription.canPlayCatalogContent
}

// Observe subscription changes
func observeSubscription() async {
    for await subscription in MusicSubscription.subscriptionUpdates {
        if subscription.canPlayCatalogContent {
            // Enable full playback UI
        } else {
            // Show subscription offer
        }
    }
}
```

### Offering Apple Music

Present the Apple Music subscription offer sheet when the user is not subscribed.
Check `canBecomeSubscriber` first, and pass `MusicSubscriptionOffer.Options` or
`onLoadCompletion` when the sheet needs contextual metadata or load-error handling.

```swift
import MusicKit
import SwiftUI

struct MusicOfferView: View {
    @State private var showOffer = false

    var body: some View {
        Button("Subscribe to Apple Music") {
            Task {
                let subscription = try? await MusicSubscription.current
                showOffer = subscription?.canBecomeSubscriber == true
            }
        }
        .musicSubscriptionOffer(
            isPresented: $showOffer,
            options: .default,
            onLoadCompletion: { error in
                if let error {
                    // Surface loading errors in app UI or diagnostics.
                    print(error)
                }
            }
        )
    }
}
```

## Playback with ApplicationMusicPlayer

`ApplicationMusicPlayer` plays Apple Music content independently from the Music app. It does not affect the system player's state.

```swift
let player = ApplicationMusicPlayer.shared

func playSong(_ song: Song) async throws {
    player.queue = [song]
    try await player.play()
}

func pause() {
    player.pause()
}

func skipToNext() async throws {
    try await player.skipToNextEntry()
}
```

### Observing Playback State

```swift
func observePlayback() {
    // player.state is an @Observable property
    let state = player.state
    switch state.playbackStatus {
    case .playing:
        break
    case .paused:
        break
    case .stopped, .interrupted, .seekingForward, .seekingBackward:
        break
    @unknown default:
        break
    }
}
```

## Queue Management

Build and manipulate the playback queue using `ApplicationMusicPlayer.Queue`.

```swift
// Initialize with multiple items
func playAlbum(_ album: Album) async throws {
    player.queue = [album]
    try await player.play()
}

// Append songs to the existing queue
func appendToQueue(_ songs: [Song]) async throws {
    try await player.queue.insert(songs, position: .tail)
}

// Insert song to play next
func playNext(_ song: Song) async throws {
    try await player.queue.insert(song, position: .afterCurrentEntry)
}
```

## Now Playing Info

Update `MPNowPlayingInfoCenter` so the Lock Screen, Control Center, and CarPlay
display current track metadata. This is essential when playing custom audio
(non-MusicKit sources). `ApplicationMusicPlayer` handles this automatically for
Apple Music content.

```swift
import MediaPlayer

func updateNowPlaying(title: S