iOS 8專輯封面

Question

自iOS 8以來，所有iPad專用藝術數據陣列& iPhone設備都會返回一個空數組。從本地文件（NSBundle）拉出時，我可以獲得專輯封面或封面藝術，但是從iTunes或設備上購買的任何歌曲都會返回空白。

我已經更新到最新的XCode，這兩個設備，並且還有在iTunes上最新的iOS。我已經在iPad 4，iPad Air，iPhone 5，iPhone 6上進行了測試。希望有人知道發生了什麼，它現在好像是iOS 8中的一個已知錯誤。另外，我可以播放資產並檢索歌曲名稱和藝術家等內容。

MPMediaQuery *songQuery = [MPMediaQuery songsQuery]; 
NSArray *itemsFromGenericQuery = [songQuery items]; 
NSMutableArray *songsList = [[NSMutableArray alloc] initWithArray:itemsFromGenericQuery]; 
MPMediaItem *mediaItem = (MPMediaItem *)[songsList objectAtIndex:0]; 

NSURL *url = [mediaItem valueForProperty:MPMediaItemPropertyAssetURL]; 
AVAsset *asset = [[AVURLAsset alloc] initWithURL:url options:nil]; 
NSArray *commonArray = [assets commonMetadata]; 

//Test A 
NSArray *albumArray = [AVMetadataItem metadataItemsFromArray:commonArray filteredByIdentifier:AVMetadataIdentifieriTunesMetadataCoverArt]; 
NSLog(@"commonArray = %lu",(unsigned long)[commonArray count]); //Returns 3 
NSLog(@"albumArray has %lu",(unsigned long)[albumArray count]); //Returns 0 or null 

//Test B 
for (AVMetadataItem *metadataItem in asset.commonMetadata) { 

    if ([metadataItem.commonKey isEqualToString:@"artwork"]){ 
     NSDictionary *imageDataDictionary = (NSDictionary *)metadataItem.value; 
     NSData *imageData = [imageDataDictionary objectForKey:@"data"]; 
     UIImage *image = [UIImage imageWithData:imageData]; 
     coverArtImage.image = image; 
    } 
} 

//Test C 
for (AVMetadataItem *item in commonArray) { 

    if ([item.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) { 
     NSData *newImage = [item.value copyWithZone:nil]; 
     coverArtImage.image = [UIImage imageWithData:newImage]; 
    } 

} 

//Test D 
for (AVMetadataItem *item in asset.metadata) { 

    if ([item.commonKey isEqualToString:@"artwork"]){ 
     NSDictionary *imageDataDictionary = (NSDictionary *)item.value; 
     NSData *imageData = [imageDataDictionary objectForKey:@"data"]; 
     UIImage *image = [UIImage imageWithData:imageData]; 
     coverArtImage.image = image; 
    } 

    if ([item.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) { 
     NSData *newImage = [item.value copyWithZone:nil]; 
     coverArtImage.image = [UIImage imageWithData:newImage]; 
    } 

} 

所有封面圖片返回null或永遠不會被調用。此外，從蘋果建議的直接文件中提取封面圖片是異步的，但無論使用什麼設備，似乎至少需要10秒。 iOS 7允許我們直接從mediaItem中拉出封面，這是瞬間的，我不明白他們爲什麼會削弱這個功能。

Answer 1

我會建議您嘗試新雨燕的實現：

let query = MPMediaQuery.songsQuery() 
let mediaCollection = MPMediaItemCollection(items: query.items!) 
print(mediaCollection.items) 

這將返回一個非空數組用於下載的歌曲的物理設備。

Answer 2

NSString *queryString = [url query]; 
if (queryString == nil) // shouldn't happen 
    return nil; 

NSArray *components = [queryString componentsSeparatedByString:@"="]; 
if ([components count] < 2) // also shouldn't happen 
    return nil; 

id trackId = [components objectAtIndex:1]; 

MPMediaQuery *query = [[MPMediaQuery alloc] init]; 
[query addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:trackId forProperty:MPMediaItemPropertyPersistentID]]; 

NSArray *items = [query items]; 

[query release]; 

if ([items count] < 1) // still shouldn't happen 
    return nil; 

MPMediaItem* mpitem= [items objectAtIndex:0]; 

MPMediaItemArtwork* mpArt = [mpitem valueForProperty:MPMediaItemPropertyArtwork]; 

UIImage* mpImage = [mpArt imageWithSize:mpArt.bounds.size];