iPhone sdk，保存MPMediaItemCollection？

Question

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。我认为使用MPMediaQuery是可行的。看来，我应该使用MPMediaItemPropertyPersistentID，但我不知道如何查询它。有什么想法吗？

Answer 1

伙计，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

这应该有效：

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

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