iPhone sdk，保存MPMediaItemCollection？

Question

我有我的应用程序显示MPMediaPickerController。我想保存MediaItem并在启动时重新开始播放。我认为这是可行的使用MPMediaQuery。看来，我应该使用MPMediaItemPropertyPersistentID，但我不确定如何查询它。有什么想法吗？

Answer 1

人，你不需要保存mediaCollection。媒体集合，它只是MPMediaItem对象的数组。所以你最好保存这些项目的persistentIds。这很容易

//it's how to know persistentId of the song after you got mediaItemCollection from your mediaPickerViewController 
//then you can sav it in userDefaults. 
- (NSNumber *)getPersistentId :(MPMediaItemCollection *)collection atIndex:(int)index { 
MPMediaItem *mediaItem = [collection.items objectAtIndex:index]; 
NSNumber *anId = [mediaItem valueForProperty:MPMediaItemPropertyPersistentID]; 
return anId; 
} 

//when your application will be launched next time you can get required song: 
- (void)obtainSongWitId:(NSNumber *)persistentId { 
MPMediaQuery *query = [MPMediaQuery songsQuery]; 
MPMediaPropertyPredicate *predicate = [MPMediaPropertyPredicate predicateWithValue:persistentId forProperty:MPMediaItemPropertyPersistentID]; 
[query addFilterPredicate:predicate]; 
NSArray *mediaItems = [query items]; 
//this array will consist of song with given persistentId. add it to collection and play it 
MPMediaItemCollection *col = [[MPMediaItemCollection alloc] initWithItems:mediaItems]; 
///.... 
[col release]; 
} 

Answer 2

这应该工作：

MPMediaQuery *query = [MPMediaQuery songsQuery]; 
MPMediaPropertyPredicate *predicate = [MPMediaPropertyPredicate predicateWithValue:myPersistentID forProperty:MPMediaItemPropertyPersistentID]; 

[query addFilterPredicate:predicate]; 
NSArray *songs = [query items];