如何使用MPMediaItemPropertyPersistentID在iPhone音乐播放器框架中播放音乐？ [英] How do you use MPMediaItemPropertyPersistentID to play music in iPhone Music Player Framework?

问题描述

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

My code sucessfully catalogs song names and ID's for my the entire music library. However, it will not actually play a song using this methodology and the console displays the following:

消息播放状态超时。

消息nowPlayingItem超时。

Message nowPlayingItem timed out.

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];

推荐答案

我将再一次回答我自己的问题。问题是collectionWithItems：需要一个MPMediaItems数组，而不是MPMediaItemPropertyPersistentIDs数组。以下是可能遇到同样问题的人的工作代码：

Once again, I'll answer my own question. The issue was that collectionWithItems: expects an array of MPMediaItems, not an array of MPMediaItemPropertyPersistentIDs. Here is the working code for anyone who may have the same problem:

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];

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