用`alamofire`跟踪已经下载的文件

Question

我如何在alamofireswift 2.1中保留已下载文件的轨道或记录，以便我不必再次下载相同的文件？我们是否有任何本地方法，由alamofire提供，或者我们必须在下载目录中的任何文件之前进行检查，如果我们已经有了那个名字的文件吗？我是如何用适当的方法

做到这一点困惑，如果有人将清除我对这样的困惑，然后它会为我有这样的帮助的感谢

UPDATE：

 let documentsURL = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0] 
    let fileUrl = documentsURL.URLByAppendingPathComponent(suggestedFileName) 

    print(fileUrl) 

    if !(NSFileManager.defaultManager().fileExistsAtPath(fileUrl.path!)){ 

     self.suggestedFileName = (self.request?.response?.suggestedFilename)! // here how can i get the suggested download name before starting the download preocess ??? 

     print("\(destination)") 
     request = Alamofire.download(.GET, "http://contentserver.adobe.com/store/books/GeographyofBliss_oneChapter.epub", destination: destination) 
      .progress { bytesRead, totalBytesRead, totalBytesExpectedToRead in 
       print(totalBytesRead) 






       // This closure is NOT called on the main queue for performance 
       // reasons. To update your ui, dispatch to the main queue. 
       dispatch_async(dispatch_get_main_queue()) { 
        print("Total bytes read on main queue: \(totalBytesRead)") 

        self.progressView.setProgress(Float(totalBytesRead)/Float(totalBytesExpectedToRead), animated: true) 
       } 
      } 
      .response { _, _, _, error in 
       if let error = error { 
        print("Failed with error: \(error)") 
       } else { 
        print("Downloaded file successfully") 
       } 
     } 

    }else { 


     print("file already exists") 

    } 

在

以上更新试图得到alamofire生成suggestedFileName，但有一个问题，当我试图得到sugestedFileName像这样：suggestedFileName = (request?.response?.suggestedFilename)! in viewdidload因为没有suggestedFileName因为没有suggestedFileName，因为下载尚未开始，所以我questio n是我怎么能从response开始下载之前得到suggestedFileName？

Answer 1

根据文档https://github.com/Alamofire/Alamofire#downloading，你可以下载到一个文件。如果您的文件目的地名称是可预测的，您可以简单地检查文件的内容是否存在。例如，如果您正在下载的数据：

if let data = NSData(contentsOfURL: yourDestinationURL) { 
    //Do your stuff here 
} 
else { 
    //Download it 
} 

如果你想要的名称保持一致，我建议你避免Alamofire建议的目标，并做到这一点，而不是：

let path = NSFileManager.defaultManager().URLsForDirectory(.ApplicationSupportDirectory, inDomains: .UserDomainMask)[0] as NSURL 
let newPath = path.URLByAppendingPathComponent(fileName) 
    Alamofire.download(.GET, "https://httpbin.org/stream/100", destination: { _ in 
    newPath //You have to give the destination in this closure. We could say 'return newPath' instead, they're the same thing. 
    }) 
    .progress({ _ in 
    //progress stuff 
    }) 
    .response { _, _, data, _ in 
    //Handle response once it's all over 
}