从音乐曲目获取信息的问题

Question

我想从音乐曲目中获得一些信息，一切正常，但一些音乐没有title，artist和cover artwork，在这种情况下，我必须提供一个默认值，例如Unknown。

我填写表格视图与轨道的信息是这样的：

//MARK: - Get Data From Track : 
func getDataFromTrack(file:URL) { 

    //Get data from track 
    urlAsset = AVURLAsset(url: file) 
    for format in urlAsset.availableMetadataFormats { 

     for metadata in urlAsset.metadata(forFormat: format) { 

      //Track Name : 
      if metadata.commonKey == "title" { 
       if let title = metadata.stringValue { 
        appDefaults.setTrack(Name: title) 
       } else { 
        appDefaults.setTrack(Name: "Unknown") 
       } 
      } 



       //Track Artist: 
      if metadata.commonKey == "artist" { 
        if let artist = metadata.stringValue { 
         appDefaults.setArtist(Name: artist) 
        } else { 
         appDefaults.setArtist(Name: "Unknown") 
        } 
       } 


      //Track Cover: 
      if metadata.commonKey == "artwork" { 
       if let data = metadata.dataValue { 
        let image = UIImage(data: data) 
        appDefaults.setCover(Image: image!) 
       } else { 
        appDefaults.setCover(Image: #imageLiteral(resourceName: "Defualt cover")) 
       } 
      } 


      appDefaults.setTrack(duration: Float(CMTimeGetSeconds(urlAsset.duration))) 
     } 
    } 
} 

在表格视图：

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { 


... setup cell 

let fileName = player.MP3DirectoryFiles[indexPath.row-2] as! NSString 
      let absoluteFileName = String(describing: fileName.lastPathComponent) 
      let removeSpaceString = absoluteFileName.replacingOccurrences(of: "%20", with: " ") 


      //Get MP3 Infromations 
      let documentsURL = NSURL(fileURLWithPath: NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true).first!,isDirectory: true) 
      let urlToMyPath = documentsURL.appendingPathComponent(removeSpaceString)! 

      player.getDataFromTrack(file: urlToMyPath) 

} 

如果没有从一个磁道单元中的数据填充其数据与其他轨道例如标题信息！

我试图让这样的零值，但并没有帮助我：

if metadata.commonKey == "artist" { 
        if let artist = metadata.stringValue { 
         appDefaults.setArtist(Name: artist) 
        } else { 
         appDefaults.setArtist(Name: "Unknown") 
        } 
       } 

Answer 1

首先尝试设置默认值，然后如果更新它们，当相应的标签找到资产：

//MARK: - Get Data From Track : 
func getDataFromTrack(file:URL) { 
    // Set defaults 
    appDefaults.setTrack(Name: "Unknown") 
    appDefaults.setArtist(Name: "Unknown") 
    appDefaults.setCover(Image: #imageLiteral(resourceName: "Defualt cover")) 
    appDefaults.setTrack(duration: Float(CMTimeGetSeconds(urlAsset.duration))) 

    //Get data from track 
    urlAsset = AVURLAsset(url: file) 
    for format in urlAsset.availableMetadataFormats { 
     for metadata in urlAsset.metadata(forFormat: format) { 

      //Track Name : 
      if metadata.commonKey == "title" { 
       if let title = metadata.stringValue, !title.isEmpty { 
        appDefaults.setTrack(Name: title) 
       } 
      } 

      //Track Artist: 
      if metadata.commonKey == "artist" { 
       if let artist = metadata.stringValue, !artist.isEmpty { 
        appDefaults.setArtist(Name: artist) 
       } 
      } 

      //Track Cover: 
      if metadata.commonKey == "artwork" { 
       if let data = metadata.dataValue { 
        let image = UIImage(data: data) 
        appDefaults.setCover(Image: image!) 
       } 
      } 
     } 
    } 
} 

如果资产不包含适当的密钥，则您将不会调用您尝试设置默认值的代码。此外，在for循环中设置轨道持续时间将导致它不必要地多次执行。