how to get mp3 file's artwork in swift(important because the objectc method doesn't work)

I found many oc method said using this code

*******metadata is a AVMetadataItem class

 NSString *path =[ [NSBundle mainBundle]  pathForResource:@"musicname" ofType:@"mp3"];

     NSURL  *fileURL = [NSURL  fileURLWithPath:path];

      AVURLAsset *avURLAsset = [[AVURLAsset alloc] initWithURL:fileURL options:nil];

      for (NSSting *format  in [avURLAsset availableMetadataFormats]){

              for (AVMetadataItem *metadata in [avURLAsset metadataForFormat:format]){

                  if([metadata.commonKey isEqualToString:@"title"]){

                        NSSting *title = (NSSting *)metadata.value;

                   }

                  if([metadata.commonKey isEqualToString:@"artwork"]){

                       UIImage *coverImage = [UIImage imageWithData:[(NSDictionary *)metadata.value objectForKey:@"data"]];

                  }


               }

      }

I use swift to programming so i try to do that in swift like this

func getArtworkForTrack(trackNumber: Int) -> NSData {
    let asset = trackAVURLAssets[trackNumber]
    var artworkData: NSData = NSData()
    for metadata in asset.metadata {
        if let commonKey = metadata.commonKey {
            if commonKey == "artwork" {
                if let keySpace = metadata.keySpace {
                    if keySpace == AVMetadataKeySpaceiTunes {
                        print("keyspace == AVMetadataKeySpaceiTunes")
                        artworkData = (metadata.value?.copyWithZone(nil))! as! NSData
                    } else {
                        let dic = metadata.value as! NSDictionary
                        let image = UIImage(data: dic.objectForKey("data") as! NSData)
                    }
                }
            }
        }
    }

    return artworkData
}

But when I run , it comes a runtime error:

Could not cast value of type '__NSCFData' (0xbdbe94) to 'NSDictionary' (0xbdc394).
(lldb) 

at this line:

let dic = metadata.value as! NSDictionary

who can tell me how to solve the problem THX!

If an AVMetadataItem value is in raw data format, it should be accessible with .dataValue.

In your case, probably something like this:

if let data = metadata.dataValue {
    let image = UIImage(data: data)
}