播放从保存的 persistentid 列表中检索到的 iPod 播放列表

Posted 2023-03-14

【中文标题】播放从保存的 persistentid 列表中检索到的 iPod 播放列表

【英文标题】：Play iPod playlist retrieved from a saved persistentid list

【发布时间】：2011-04-18 12:15:28

【问题描述】：

我保存了使用媒体选择器选择的歌曲的持久 ID，现在我正在尝试创建队列以播放该列表，但这段代码有问题：

myPlayer = [MPMusicPlayerController applicationMusicPlayer];

    NSMutableArray *canzonilist = [[[NSMutableArray alloc] initWithCapacity:1] retain];
    NSData *data = [[NSUserDefaults standardUserDefaults] objectForKey:@"listaCanzoni"];
    NSArray *decodedData = [NSKeyedUnarchiver unarchiveObjectWithData:data];
    [canzonilist addObjectsFromArray:decodedData];

    MPMediaQuery *songQuery = [MPMediaQuery songsQuery];
    for (int i = 0; i > [canzonilist count]; i++) 
        [songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:[canzonilist objectAtIndex:i] forProperty:MPMediaItemPropertyPersistentID]];
    
    NSArray *songs = [songQuery items];
    MPMediaItemCollection *currentQueue = [[MPMediaItemCollection alloc] initWithItems:songs];

    if (currentQueue != nil)     
        [myPlayer setQueueWithItemCollection:currentQueue];
     else 
        [myPlayer setQueueWithQuery: [MPMediaQuery songsQuery]];
    

    [myPlayer play];
    [canzonilist release];
    [currentQueue release];

谢谢

【参考方案1】：

终于找到了解决办法：

保存：

    - (void) mediaPicker: (MPMediaPickerController *) mediaPicker didPickMediaItems: (MPMediaItemCollection *) mediaItemCollection 

    [self savePlaylist:mediaItemCollection];

    [self dismissModalViewControllerAnimated: YES];



- (void)savePlaylist:(MPMediaItemCollection *) mediaItemCollection 

    NSArray* items = [mediaItemCollection items];

    NSMutableArray* listToSave = [[NSMutableArray alloc] initWithCapacity:0];

    for (MPMediaItem *song in items) 

        NSNumber *persistentId = [song valueForProperty:MPMediaItemPropertyPersistentID];

        [listToSave addObject:persistentId];

    

    NSData *data = [NSKeyedArchiver archivedDataWithRootObject: listToSave];

    [[NSUserDefaults standardUserDefaults] setObject:data forKey:@"songsList"];

    [[NSUserDefaults standardUserDefaults] synchronize];

    [listToSave release];

加载

- (void)setupMusic 

     myPlayer = [MPMusicPlayerController applicationMusicPlayer];

     if ([[NSUserDefaults standardUserDefaults] objectForKey:@"songsList"] != nil) 

         NSMutableArray *theList = [[NSMutableArray alloc] initWithCapacity:0];

         NSData *data = [[NSUserDefaults standardUserDefaults] objectForKey:@"songsList"];

         NSArray *decodedData = [NSKeyedUnarchiver unarchiveObjectWithData:data];

         [theList addObjectsFromArray:decodedData];

         NSMutableArray *allTheSongs = [[NSMutableArray alloc] initWithCapacity:0];

         for (int i = 0; i < [theList count]; i++) 

             MPMediaQuery *songQuery = [MPMediaQuery songsQuery];

             [songQuery addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:[theList objectAtIndex:i] forProperty:MPMediaItemPropertyPersistentID]];

             NSArray *songs = [songQuery items];

             [allTheSongs addObjectsFromArray: songs];

         

         MPMediaItemCollection *currentQueue = [[MPMediaItemCollection alloc] initWithItems:allTheSongs];

         [myPlayer setQueueWithItemCollection:currentQueue];

         [theList release];

         [currentQueue release];

         [allTheSongs release];

     else 

        [myPlayer setQueueWithQuery: [MPMediaQuery songsQuery]];

        [myPlayer setShuffleMode: MPMusicShuffleModeSongs]; //optional