ios4 - 你如何使用 MPMediaItem Property Persistent IS 在 iPhone Music Player Framework 中播放音乐？

Question

我的代码成功地为我的整个音乐库编目了歌曲名称和 ID。但是，它实际上不会使用这种方法播放歌曲，并且控制台会显示以下内容:

消息播放状态超时。

消息 nowPlayingItem 超时。

self.musicPlayer = [MPMusicPlayerController applicationMusicPlayer];

MPMediaQuery *everything = [[MPMediaQuery alloc] init];
NSArray *itemsFromGenericQuery = [everything items];
SongName = [[NSMutableArray alloc] init];
SongItem = [[NSMutableArray alloc] init];
NSString *songTitle;
NSString *songID;
//Collect names & ID for entire music library & put into arrays
for (MPMediaItem *song in itemsFromGenericQuery) {
songTitle = [song valueForProperty: MPMediaItemPropertyTitle];
[SongName addObject:songTitle];
songID = [song valueForProperty: MPMediaItemPropertyPersistentID];
[SongItem addObject:songID];
}

NSLog (@"%@", [SongName objectAtIndex:1]);
NSLog (@"%@", [SongItem objectAtIndex:1]);
// Play the second song in the list
MPMediaItemCollection *collection = [MPMediaItemCollection collectionWithItems:[NSArray arrayWithObject:[SongItem objectAtIndex:1]]];
[self.musicPlayer setQueueWithItemCollection:collection];
[self.musicPlayer play];

Answer 1

我再一次回答我自己的问题。问题是 collectionWithItems: 需要一组 MPMediaItems，而不是一组 MPMediaItemPropertyPersistentID。以下是可能遇到相同问题的任何人的工作代码:

MPMediaQuery *everything = [[MPMediaQuery alloc] init];
NSArray *itemsFromGenericQuery = [everything items];
SongItem = [[NSMutableArray alloc] init];
for (MPMediaItem *song in itemsFromGenericQuery) {
   NSString *songTitle = [song valueForProperty: MPMediaItemPropertyTitle];
   //NSLog (@”%@”, songTitle);
   songID = [song valueForProperty: MPMediaItemPropertyPersistentID];
   //NSLog (@”%@”, songID);
   [SongItem addObject:songID];
}

//Choose the first indexed song
NSString *selectedTitle = [SongItem objectAtIndex:0];

//Use the MPMediaItemPropertyPersistentID to play the song
MPMediaPropertyPredicate *predicate = [MPMediaPropertyPredicate predicateWithValue:selectedTitle forProperty:MPMediaItemPropertyPersistentID];
MPMediaQuery *mySongQuery = [[MPMediaQuery alloc] init];
[mySongQuery addFilterPredicate: predicate];
[musicPlayer setQueueWithQuery:mySongQuery];
[musicPlayer play];