iOS 如何在后台下载多个 mp4 文件？

Question

我从过去 2 天开始就一直在这个问题上。请帮帮我。

我的要求是，如果我在第二个视图控制器中在后台下载文件，并且在下载开始后我弹出到第一个视图控制器，如果我再次推送到第二个视图控制器，那么应该继续该进程。

这里发生了什么：

我推送到第二个视图控制器。
我使用 NSMutableURLRequest、NSURLConnection 开始下载。
如果我弹出到第一个视图控制器并再次转到第二个视图控制器，那么所有都显示为 0。意味着如果在弹出期间进度为 34%，然后再次推送时间，它的 0% 显示在我的 UI 中，但是下载照常进行。

我的日志也显示完美，但 UI 没有显示。我尝试了所有的答案。都是一样的问题。

这是我的全部代码：

在应用委托方法中：

CTAppDelegate.h

@property (copy) void (^backgroundSessionCompletionHandler)();

CTAppDelegate.m

- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler
{
    self.backgroundSessionCompletionHandler = completionHandler;
}

2ndViewController.h

- (IBAction)downloadBackground:(id)sender;
- (IBAction)downloadImage:(id)sender;
@property (strong, nonatomic) IBOutlet UIImageView *downloadedImage;
@property (strong, nonatomic) IBOutlet UIProgressView *progressView;
@end

2ndViewController.m

#import "CTViewController.h"
#import "CTSessionOperation.h"
#import "CTAppDelegate.h"

static NSString *downloadUrl =     @"http://www.nasa.gov/sites/default/files/ladee_9.4.13_nasa_edge_0.jpg";

@interface CTViewController ()

@property (nonatomic, strong) NSOperation *downloadOperation;

@end

@implementation CTViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    self.progressView.progress = 0;
    self.downloadedImage.hidden = NO;
    self.progressView.hidden = YES;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)downloadBackground:(id)sender {
//    [self downloadImageInBackground:YES];

    [self.navigationController popViewControllerAnimated:YES];
}

- (IBAction)downloadImage:(id)sender {
    [self downloadImageInBackground:NO];
}

- (void)downloadImageInBackground:(BOOL)background{
   if (self.downloadOperation){
       return;
   }

    CTSessionOperation *operation = [CTSessionOperation new];
    operation.downloadUrl = downloadUrl;
    operation.progressAction = ^(double bytesWritten, double bytesExpected){
        double progress = bytesWritten / bytesExpected;
       dispatch_async(dispatch_get_main_queue(), ^{
        self.progressView.progress = (float) progress;
        });
     };
     operation.completionAction = ^(NSURL *imageUrl, BOOL success){
        dispatch_async(dispatch_get_main_queue(), ^{
             if (success){
                 UIImage *image = [UIImage imageWithContentsOfFile:[imageUrl path]];
                 self.downloadedImage.image = image;
                 NSLog(@"Done.......");
              }
             self.downloadedImage.hidden = NO;
             self.progressView.progress = 0;
             self.progressView.hidden = YES;
             self.downloadOperation = nil;
         });
     };
     operation.isBackground = background;

     [operation enqueueOperation];
     self.downloadedImage.hidden = YES;
     self.progressView.hidden = NO;
     self.downloadOperation = operation;
  }

  @end

Operation.h

  #import <Foundation/Foundation.h>

  typedef void (^CTProgressBlock)(double totalBytesWritten, double bytesExpected);
  typedef void (^CTCompletionBlock)(NSURL *imageUrl, BOOL success);

  @interface CTSessionOperation : NSOperation<NSURLSessionDelegate,    NSURLSessionTaskDelegate, NSURLSessionDownloadDelegate>

  @property (nonatomic) NSURLSessionDownloadTask *downloadTask;
  @property (nonatomic) NSURLSession *session;
  @property (nonatomic, strong) NSString *downloadUrl;
  @property (strong) CTProgressBlock progressAction;
  @property (strong) CTCompletionBlock completionAction;
  @property (nonatomic, assign) BOOL isBackground;

  - (void)enqueueOperation;
  @end

Operation.m

  #import "CTSessionOperation.h"
  #import "CTAppDelegate.h"

  @implementation CTSessionOperation

  - (NSOperationQueue *)operationQueue{
         static NSOperationQueue *operationQueue = nil;
         static dispatch_once_t onceToken;
         dispatch_once(&onceToken, ^{
               operationQueue = [NSOperationQueue new];
               [operationQueue setMaxConcurrentOperationCount:NSOperationQueueDefaultMaxConcurrentOperationCount];
         });

        return operationQueue;
    }

    - (NSURLSession *)session {
         static NSURLSession *session = nil;
         static NSURLSession *backgroundSession = nil;
         static dispatch_once_t onceToken;
         dispatch_once(&onceToken, ^{
              NSURLSessionConfiguration *configuration =  [NSURLSessionConfiguration defaultSessionConfiguration];
              session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
              NSURLSessionConfiguration *backgroundConfiguration = [NSURLSessionConfiguration
         backgroundSessionConfiguration:@"com.captech.NSURLSample.BackgroundSession"];
              backgroundSession = [NSURLSession sessionWithConfiguration:backgroundConfiguration
                                                      delegate:self
                                                 delegateQueue:nil];
             });

          return self.isBackground ? backgroundSession : session;
    }

    - (void)enqueueOperation{
          [[self operationQueue] addOperation:self];
    }

    #pragma mark - NSOperation

    - (void)start {
         if (!self.isCancelled){
                NSURL *downloadURL = [NSURL URLWithString:self.downloadUrl];
                NSURLRequest *request = [NSURLRequest requestWithURL:downloadURL];

                self.downloadTask = [self.session downloadTaskWithRequest:request];
                [self.downloadTask resume];
          }
     }

     #pragma mark - NSURLSessionDownloadDelegate
     - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
        NSFileManager *fileManager = [NSFileManager defaultManager];

        NSArray *urls = [fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
        NSURL *documentsDirectory = [urls objectAtIndex:0];

        NSURL *originalUrl = [[downloadTask originalRequest] URL];
NSURL *destinationUrl = [documentsDirectory URLByAppendingPathComponent:[originalUrl lastPathComponent]];
         NSError *error;

        [fileManager removeItemAtURL:destinationUrl error:NULL];
          BOOL success = [fileManager copyItemAtURL:location toURL:destinationUrl error:&error];
          if (self.completionAction){
                 self.completionAction(destinationUrl, success);
           }
     }

       - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
              if (downloadTask == self.downloadTask && self.progressAction){
              self.progressAction((double)totalBytesWritten, (double)totalBytesExpectedToWrite);
           }
     }

     - (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes {

     }

    #pragma mark - NSURLSessionTaskDelegate

    - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
        if (self.progressAction){
               self.progressAction((double)task.countOfBytesReceived, (double)task.countOfBytesExpectedToReceive);
        }

         self.downloadTask = nil;
    }

     #pragma mark - NSURLSessionDelegate

      - (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
           CTAppDelegate *appDelegate = (CTAppDelegate *)[[UIApplication sharedApplication] delegate];
           if (appDelegate.backgroundSessionCompletionHandler) {
                 void (^completionHandler)() =  appDelegate.backgroundSessionCompletionHandler;
             appDelegate.backgroundSessionCompletionHandler = nil;
    completionHandler();
           }
     }

     @end

这是我的完整代码。请检查这个... :)

Answer 1

我处理下载的方式与您的处理方式略有不同:)

这是我的处理方式:)

1.Declare 一个 NSOperation class 并将下载文件的代码移动到这个 class

2.Declare 您的 NSOpertaion class 中的一个协议，它将向确认此协议的任何人通知当前下载状态

3.In 你的第二个 VC 启动 NSOpertaion 并选择委托 :) 并相应地更新你的进度

在你的第二个VC的viewWillDisappear中删除它作为委托并在第二个的ViewWillAppear中将它作为委托添加回NSOperationVC

这里有一些相同的代码:)

downloadAssets.h

#import <Foundation/Foundation.h>

@protocol AssetDownloadStatusProtocol <NSObject>
-(void)updateStatusWithValue:(float) progress;
@end

@interface downloadAssets : NSOperation
@property (nonatomic,weak) id<AssetDownloadStatusProtocol> delegate;
@property (nonatomic,strong) NSString *urlToDownload;
-(id)initWithURL:(NSString *)url;
@end

downloadAssets.m

    @implementation downloadChatAssets

-(id)initWithURL:(NSString *)url{
    self=[super init];
    self.urlToDownload = url;
    appdelegate=(AppDelegate *)[[UIApplication sharedApplication] delegate];
    return self;
}

- (void)main {
    // a lengthy operation
    @autoreleasepool {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            if (self.isCancelled) {
                appdelegate.downloadingOperation = nil;
                return;
            }
            else{
                NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
                AFURLSessionManager *manager = ... //start downloading

                NSURLSessionDataTask *dataTask = [manager dataTaskWithRequest:URLRequest uploadProgress:nil downloadProgress:^(NSProgress * _Nonnull downloadProgress) {
                    if (self.isCancelled) {
                        appdelegate.downloadingOperation = nil;
                        return;
                    }
                    self.progressAmount = downloadProgress.fractionCompleted;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        [self.delegate updateStatusWithValue:self.progressAmount];
                    });
                } completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
                    //handle completion here
                }];

                [dataTask resume];
            }
        });
    }
}
@end

AppDelegate.h

@property (nonatomic, Strong) NSOperation *downloadingOperation;

SecondVC.h

@interface SecondVC : UIViewController <AssetDownloadStatusProtocol>

SecondVC.m

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:YES];
    if(appdelegate.downloadingOperation) {
          appdelegate.downloadingOperation.delegate = self;
    }
}

-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:YES];
    if(appdelegate.downloadingOperation) {
           appdelegate.downloadingOperation.delegate = nil;
    }
}

-(void)updateStatusWithValue:(float)progress{
    dispatch_async(dispatch_get_main_queue(), ^{
        //update your progress here
        [self.progressView updateProgressBarWithProgressValue:progress];
    });
}

就是这样 :)

随时开始下载操作:)

appdelegate.downloadingOperation = yourDownloaderOperation;
[yourDownloaderOperation start];

你想阻止它说

[yourDownloaderOperation stop];

有不止一个下载操作??考虑使用 NSOperationQueue 或 Array 在 appdelegate 中保存 NSOperations :)

编辑

根据您在评论中的要求，您可以在 appDelegate 中保留对 CTOperation 的引用。

@property (nonatomic, Strong) CTOperation *downloadingOperation;

您不需要声明协议，因为您已经声明了完成块和 progressActionBlock :)

您所要做的就是检查您的 SecondVC viewWillAppear。

-(void)viewWillAppear:(BOOL)animated{
        [super viewWillAppear:YES];
        if(appdelegate.downloadingOperation) {
              appdelegate.downloadingOperation.progressAction = ^(double bytesWritten, double bytesExpected){
    double progress = bytesWritten / bytesExpected;
   dispatch_async(dispatch_get_main_queue(), ^{
    self.progressView.progress = (float) progress;
    });
 };
 appdelegate.downloadingOperation.completionAction = ^(NSURL *imageUrl, BOOL success){
    dispatch_async(dispatch_get_main_queue(), ^{
         if (success){
             UIImage *image = [UIImage imageWithContentsOfFile:[imageUrl path]];
             self.downloadedImage.image = image;
             NSLog(@"Done.......");
          }
         self.downloadedImage.hidden = NO;
         self.progressView.progress = 0;
         self.progressView.hidden = YES;
         self.downloadOperation = nil;
     });
 };
        }
    }

    -(void)viewWillDisappear:(BOOL)animated{
        [super viewWillDisappear:YES];
        if(appdelegate.downloadingOperation) {
               appdelegate.downloadingOperation.progressAction = nil;
               appdelegate.downloadingOperation.completionAction = nil;
        }
    }

并在您的 downloadImageInBackground 方法中而不是 self.downloadOperation = operation; 说 `appdelegate.downloadingOperation = operation;

免责声明

请注意，此答案中提供的代码仅用于解释概念。我可能有句法或符号错误。请勿盲目复制粘贴

简单吧？？？有疑问，请联系我 :) 编码愉快 :)

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