目標C：多個下載

Question

我正在嘗試製作一個從在線服務器下載pdf文件的應用程序。 我做的是我創建了3個按鈕，它有3個不同的URL並將其保存到應用程序的沙箱並在iBooks中打開它。

但它崩潰的應用程序，我有這個錯誤說...

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSURL initFileURLWithPath:]: nil string parameter' *** 

這裏是我的代碼： 在按鈕點擊：

 if (sender.tag == 1) { 
     pdfTag = 1; 
     pdfSource1 = @"http://myweb.com/folder/folderagain/file1.pdf"; 
     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pdfSource1]]; 
     NSURLConnection *conn = [[NSURLConnection alloc] init]; 
     (void)[conn initWithRequest:request delegate:self]; 

     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); 
     dispatch_async(queue, ^{ 
      dataSource1 = [NSData dataWithContentsOfURL:[NSURL URLWithString:pdfSource1]]; 
      dispatch_sync(dispatch_get_main_queue(), ^{ 
      }); 
      pdfSourcePath1 = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"myPDF1.pdf"]; 
      NSLog(@"PDF path: %@",pdfSourcePath1); 
      [dataSource1 writeToFile:pdfSourcePath1 atomically:YES]; 
     }); 

    } else if (sender.tag == 2) { 
     pdfTag = 2; 
     pdfSource2 = @"http://myweb.com/folder/folderagain/file2.pdf"; 
     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pdfSource2]]; 
     NSURLConnection *conn = [[NSURLConnection alloc] init]; 
     (void)[conn initWithRequest:request delegate:self]; 

     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); 
     dispatch_async(queue, ^{ 
      dataSource2 = [NSData dataWithContentsOfURL:[NSURL URLWithString:pdfSource2]]; 
      dispatch_sync(dispatch_get_main_queue(), ^{ 
      }); 
      pdfSourcePath2 = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"myPDF2.pdf"]; 
      NSLog(@"PDF path: %@",pdfSourcePath2); 
      [dataSource2 writeToFile:pdfSourcePath2 atomically:YES]; 
     }); 
    } else if (sender.tag == 3) { 
     pdfTag = 3; 
     pdfSource3 = @"http://myweb.com/folder/folderagain/file3.pdf"; 
     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pdfSource3]]; 
     NSURLConnection *conn = [[NSURLConnection alloc] init]; 
     (void)[conn initWithRequest:request delegate:self]; 

     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); 
     dispatch_async(queue, ^{ 
      dataSource3 = [NSData dataWithContentsOfURL:[NSURL URLWithString:pdfSource3]]; 
      dispatch_sync(dispatch_get_main_queue(), ^{ 
      }); 
      pdfSourcePath3 = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"myPDF3.pdf"]; 
      NSLog(@"PDF path: %@",pdfSourcePath3); 
      [dataSource3 writeToFile:pdfSourcePath3 atomically:YES]; 
     }); 
    } 

對於打開文件：

 if (pdfTag == 1) { 
    NSURL *url = [NSURL fileURLWithPath:pdfSourcePath1]; 
    docController1 = [UIDocumentInteractionController interactionControllerWithURL:url]; 

    docController1.delegate = self; 

    [docController1 presentOpenInMenuFromRect:btn1.frame inView:self.view animated:YES]; 
    } else if (pdfTag == 2) { 
     NSURL *url = [NSURL fileURLWithPath:pdfSourcePath2]; 
     docController2 = [UIDocumentInteractionController interactionControllerWithURL:url]; 

     docController2.delegate = self; 

     [docController2 presentOpenInMenuFromRect:btn2.frame inView:self.view animated:YES]; 
    } else if (pdfTag == 3) { 
     NSURL *url = [NSURL fileURLWithPath:pdfSourcePath3]; 
     docController2 = [UIDocumentInteractionController interactionControllerWithURL:url]; 

     docController2.delegate = self; 

     [docController2 presentOpenInMenuFromRect:btn3.frame inView:self.view animated:YES]; 
    } 

我希望我能找到答案。

Answer 1

在你的代碼，我不能看到initFileURLWithPath你在任何地方使用的API ..

正下方是我送給你的任務的建議，

下面是代碼獲得遠程PDF作爲一個NSData使用服務器文件路徑並存儲在應用程序沙箱中。

 NSData *pdfData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:bookUrlString]]; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"myPDF.pdf"]; 
    [pdfData writeToFile:filePath atomically:YES 

按我這個目的的理解，這並不需要任何NSURLRequest或NSURLConnection ...

Answer 2

網絡是一項複雜的工作，我絕不會建議你下載或使用上傳文件-initWithURL方法，因爲它不是異步的並且會阻塞主線程。你應該使用NSURLConnection類和它的委託方法，或只接受一個隊列和一個完成塊的驚人的類方法。
你正在做怪異的東西，你使用NSURLConnection但你使用..WithURL方法，你應該去與他們一個。
網絡上有不同的下載管理器可以幫助你完成整個過程，因爲它們包裝NSURLConnection類和委託方法。
有：

1. AFNetworking link
2. MKNetworking（我的最愛）link

Answer 3

NSData dataWithContentsOfURL作品長以及文件的大小小。

我不會建議你使用這種方法來下載大文件，而是使用NSURLConnection或AFNetworking。

如何使用NSURLConnection和AFNetworking下載下面的答案解釋文件： https://stackoverflow.com/a/16454923/2548707