Ios 有多个文件下载问题

目前我正在实现一个文件下载应用程序。 在我的应用服务器中有大约2500个资源文件，我需要将这些文件从服务器下载到我的文档目录中

我的代码：

@implementation DownloadManager
{
    NSURLSession *session;
    BOOL downloading;
}

#pragma mark - NSURLSessionDownloadDelegate

// Handle download completion from the task
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSInteger index = [self assetDownloadIndexForDownloadTask:downloadTask];
    if (index < 0)
    {
        return;
    }
    DownloadHelper *movieDownload = _assetsToDownload[index];

    // Copy temporary file
    NSError * error;
    [[NSFileManager defaultManager] copyItemAtURL:location toURL:[NSURL fileURLWithPath:[movieDownload localPath]] error:&error];
    downloading = NO;
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes
{
    // Required delegate method
}

// Handle task completion
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    if (error)
        NSLog(@"Task %@ failed: %@", task, error);
    NSLog(@"Task %@ Success: %@", task, error);
    if ([_assetsToDownload count])
    {
        [_assetsToDownload removeObjectAtIndex:0];
    }

    downloading = NO;
    if ([_assetsToDownload count])
    {
        [self downloadFiles];
    }
    else
    {
        [self downloadAssets];
    }
}

// Handle progress update from the task
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    NSInteger index = [self assetDownloadIndexForDownloadTask:downloadTask];
    if (index < 0) return;
   // DownloadHelper *movieDownload = _assetsToDownload[index];
    double progress = (double) (totalBytesWritten/1024) / (double) (totalBytesExpectedToWrite/1024);
    dispatch_async(dispatch_get_main_queue(), ^{
        // Showing progress
    });

}

#pragma mark - Movie Download Handling & UI

// Helper method to get the index of a Asset from the array based on downloadTask.
- (NSInteger)assetDownloadIndexForDownloadTask:(NSURLSessionDownloadTask *)downloadTask
{
    NSInteger foundIndex = -1;
    NSInteger index = 0;
    for (DownloadHelper *asset in _assetsToDownload)
    {
        if (asset.downloadTask == downloadTask)
        {
            foundIndex = index;
            break;
        }
        index++;
    }
    return foundIndex;
}

- (void)addAssetDownload
{
    DownloadInfo *info = nil;
    NSString *assetFolder = nil;
    for (int index = 0; index<[_assets count]; index++)
    {
        info                                    = [_assets objectAtIndex:index];
        NSURL *url                              = [NSURL URLWithString:info.assetURL];
        NSURLRequest *request                   = [NSURLRequest requestWithURL:url];
        NSURLSessionDownloadTask *downloadTask  = [session downloadTaskWithRequest:request];

        DownloadHelper *assetDownload        = [[DownloadHelper alloc] initWithURL:url downloadTask:downloadTask];
        assetDownload.assetName                 = info.assetName;

        if (info.categoryId == 1)
        {
            assetFolder = [self getImagePath:info.assetName];
        }
        else if (info.categoryId == 2)
        {
            assetFolder = [self getVideoPath:info.assetName];
        }
        else if (info.categoryId == 3)
        {
            //assetFolder = [self getDBPath:info.assetName];
        }
        else
        {
            assetFolder = [self filePath:info.assetName];
        }
        assetDownload.assetFolder = assetFolder;
        [_assetsToDownload addObject:assetDownload];
    }
}

// Initialize the download, session and tasks
- (void)initialize
{
    for (DTEDownloadHelper *movieDownload in _assetsToDownload)
    {
        // Cancel each task
        NSURLSessionDownloadTask *downloadTask = movieDownload.downloadTask;
        [downloadTask cancel];
    }

    // Cancel all tasks and invalidate the session (also releasing the delegate)
    [session invalidateAndCancel];
    session = nil;

    _assetsToDownload = [[NSMutableArray alloc] init];

    // Create a session configuration passing in the session ID
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"DTEDownloadBackground"];
    sessionConfiguration.discretionary = YES;
    session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:nil];
    [self addAssetDownload];
    // Reset the UI
    downloading = NO;
    [self downloadFiles];

}


// Download handler
- (void)downloadFiles
{
    if ([_assetsToDownload count] > 0)
    {
        // Acquire the appropriate downloadTask and respond appropriately to the user's selection
        NSURLSessionDownloadTask * downloadTask = [_assetsToDownload[0] downloadTask];
        if (downloadTask.state == NSURLSessionTaskStateCompleted)
        {
            // Download is complete.  Play movie.
            // NSURL *movieURL = [NSURL fileURLWithPath:[_assetsToDownload[0] localPath]];
        }
        else if (downloadTask.state == NSURLSessionTaskStateSuspended)
        {
            // If suspended and not already downloading, resume transfer.
            if (!downloading)
            {
                [self showHUD:[NSString stringWithFormat:@"Downloading %@",[_assetsToDownload[0] assetName]]];
                [downloadTask resume];
                downloading = YES;
            }
        }
        else if (downloadTask.state == NSURLSessionTaskStateRunning)
        {
            // If already downloading, pause the transfer.
            [downloadTask suspend];
            downloading = NO;
        }

    }
}

- (void)downloadAssets
{
    _assets = [self retreiveAssets];    // Getting the resource details from the database
    if (![_assets count])
    {
        // Hide progress
    }
    [self addAssetDownload];
    [self downloadFiles];
}
@end

@实现下载管理器
{
NSURL会议*会议；
BOOL下载；
}
#pragma标记-NSURLSessionDownloadDelegate
//处理任务中的下载完成
-（void）URLSession:（NSURLSession*）会话下载任务：（NSURLSessionDownloadTask*）下载任务未完成下载教程：（NSURL*）位置
{
NSInteger索引=[self-assetDownloadIndexForDownloadTask:downloadTask]；
如果（指数<0）
{
返回；
}
DownloadHelper*movieDownload=_assetsToDownload[index]；
//复制临时文件
n错误*错误；
[[NSFileManager defaultManager]CopyItemAttribute:location Tour:[NSURL fileURLWithPath:[movieDownload localPath]]错误：&错误]；
下载=否；
}
-（void）URLSession:（NSURLSession*）会话下载任务：（NSURLSessionDownloadTask*）下载任务DidResumeAtoOffset:（int64_t）文件偏移量预期总字节数：（int64_t）预期总字节数
{
//必需的委托方法
}
//处理任务完成
-（void）URLSession:（NSURLSession*）会话任务：（NSURLSessionTask*）任务未完成错误：（NSError*）错误
{
如果（错误）
NSLog（@“任务%@失败：%@”，任务，错误）；
NSLog（@“任务%@成功：%@”，任务，错误）；
如果（[\u assetsToDownload count]）
{
[\u assetsToDownload removeObjectAtIndex:0]；
}
下载=否；
如果（[\u assetsToDownload count]）
{
[自动下载文件]；
}
其他的
{
[自下载资产]；
}
}
//处理来自任务的进度更新
-（void）URLSession:（NSURLSession*）会话下载任务：（NSURLSessionDownloadTask*）下载任务didWriteData:（int64_t）BytesWritedTotalBytesWrited:（int64_t）TotalBytesWritedTotalBytesExpectedToWrite:（int64_t）totalBytesExpectedToWrite
{
NSInteger索引=[self-assetDownloadIndexForDownloadTask:downloadTask]；
如果（指数<0）返回；
//DownloadHelper*movieDownload=_assetsToDownload[index]；
double progress=（double）（totalBytesWrite/1024）/（double）（totalBytesExpectedToWrite/1024）；
dispatch\u async（dispatch\u get\u main\u queue（）^{
//显示进步
});
}
#pragma标记-电影下载处理和用户界面
//基于downloadTask从数组中获取资源索引的助手方法。
-（NSInteger）assetDownloadIndexForDownloadTask:（NSURLSessionDownloadTask*）downloadTask
{
NSInteger foundIndex=-1；
NSInteger指数=0；
对于（下载助手*资产在_assetsToDownload中）
{
if（asset.downloadTask==downloadTask）
{
foundIndex=索引；
打破
}
索引++；
}
收益率指数；
}
-（无效）添加组件下载
{
DownloadInfo*info=nil；
NSString*assetFolder=nil；
对于（int索引=0；索引0）
{
//获取适当的下载任务，并对用户的选择做出适当的响应
NSURLSessionDownloadTask*downloadTask=[[U assetsToDownload[0]downloadTask]；
if（downloadTask.state==NSURLSessionTaskStateCompleted）
{
//下载完成。播放电影。
//NSURL*movieURL=[NSURL fileURLWithPath:[[U assetsToDownload[0]localPath]]；
}
else if（downloadTask.state==nsurlsessiontaskstatesupspended）
{
//如果已挂起且尚未下载，请恢复传输。
如果（！正在下载）
{
[self showHUD:[NSString stringWithFormat:@“Downloading%@，[[u assetsToDownload[0]assetName]]；
[下载任务恢复]；
下载=是；
}
}
else if（downloadTask.state==NSURLSessionTaskStateRunning）
{
//如果已下载，请暂停传输。
[下载任务暂停]；
下载=否；
}
}
}
-（作废）下载资产
{
_assets=[self-retreiveAssets]；//从数据库获取资源详细信息
如果（！[\u资产计数]）
{
//隐藏进度
}
[自添加组件下载]；
[自动下载文件]；
}
@结束

问题：

@implementation DownloadManager
{
    NSURLSession *session;
    BOOL downloading;
}

#pragma mark - NSURLSessionDownloadDelegate

// Handle download completion from the task
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSInteger index = [self assetDownloadIndexForDownloadTask:downloadTask];
    if (index < 0)
    {
        return;
    }
    DownloadHelper *movieDownload = _assetsToDownload[index];

    // Copy temporary file
    NSError * error;
    [[NSFileManager defaultManager] copyItemAtURL:location toURL:[NSURL fileURLWithPath:[movieDownload localPath]] error:&error];
    downloading = NO;
}

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes
{
    // Required delegate method
}

// Handle task completion
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    if (error)
        NSLog(@"Task %@ failed: %@", task, error);
    NSLog(@"Task %@ Success: %@", task, error);
    if ([_assetsToDownload count])
    {
        [_assetsToDownload removeObjectAtIndex:0];
    }

    downloading = NO;
    if ([_assetsToDownload count])
    {
        [self downloadFiles];
    }
    else
    {
        [self downloadAssets];
    }
}

// Handle progress update from the task
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    NSInteger index = [self assetDownloadIndexForDownloadTask:downloadTask];
    if (index < 0) return;
   // DownloadHelper *movieDownload = _assetsToDownload[index];
    double progress = (double) (totalBytesWritten/1024) / (double) (totalBytesExpectedToWrite/1024);
    dispatch_async(dispatch_get_main_queue(), ^{
        // Showing progress
    });

}

#pragma mark - Movie Download Handling & UI

// Helper method to get the index of a Asset from the array based on downloadTask.
- (NSInteger)assetDownloadIndexForDownloadTask:(NSURLSessionDownloadTask *)downloadTask
{
    NSInteger foundIndex = -1;
    NSInteger index = 0;
    for (DownloadHelper *asset in _assetsToDownload)
    {
        if (asset.downloadTask == downloadTask)
        {
            foundIndex = index;
            break;
        }
        index++;
    }
    return foundIndex;
}

- (void)addAssetDownload
{
    DownloadInfo *info = nil;
    NSString *assetFolder = nil;
    for (int index = 0; index<[_assets count]; index++)
    {
        info                                    = [_assets objectAtIndex:index];
        NSURL *url                              = [NSURL URLWithString:info.assetURL];
        NSURLRequest *request                   = [NSURLRequest requestWithURL:url];
        NSURLSessionDownloadTask *downloadTask  = [session downloadTaskWithRequest:request];

        DownloadHelper *assetDownload        = [[DownloadHelper alloc] initWithURL:url downloadTask:downloadTask];
        assetDownload.assetName                 = info.assetName;

        if (info.categoryId == 1)
        {
            assetFolder = [self getImagePath:info.assetName];
        }
        else if (info.categoryId == 2)
        {
            assetFolder = [self getVideoPath:info.assetName];
        }
        else if (info.categoryId == 3)
        {
            //assetFolder = [self getDBPath:info.assetName];
        }
        else
        {
            assetFolder = [self filePath:info.assetName];
        }
        assetDownload.assetFolder = assetFolder;
        [_assetsToDownload addObject:assetDownload];
    }
}

// Initialize the download, session and tasks
- (void)initialize
{
    for (DTEDownloadHelper *movieDownload in _assetsToDownload)
    {
        // Cancel each task
        NSURLSessionDownloadTask *downloadTask = movieDownload.downloadTask;
        [downloadTask cancel];
    }

    // Cancel all tasks and invalidate the session (also releasing the delegate)
    [session invalidateAndCancel];
    session = nil;

    _assetsToDownload = [[NSMutableArray alloc] init];

    // Create a session configuration passing in the session ID
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"DTEDownloadBackground"];
    sessionConfiguration.discretionary = YES;
    session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:nil];
    [self addAssetDownload];
    // Reset the UI
    downloading = NO;
    [self downloadFiles];

}


// Download handler
- (void)downloadFiles
{
    if ([_assetsToDownload count] > 0)
    {
        // Acquire the appropriate downloadTask and respond appropriately to the user's selection
        NSURLSessionDownloadTask * downloadTask = [_assetsToDownload[0] downloadTask];
        if (downloadTask.state == NSURLSessionTaskStateCompleted)
        {
            // Download is complete.  Play movie.
            // NSURL *movieURL = [NSURL fileURLWithPath:[_assetsToDownload[0] localPath]];
        }
        else if (downloadTask.state == NSURLSessionTaskStateSuspended)
        {
            // If suspended and not already downloading, resume transfer.
            if (!downloading)
            {
                [self showHUD:[NSString stringWithFormat:@"Downloading %@",[_assetsToDownload[0] assetName]]];
                [downloadTask resume];
                downloading = YES;
            }
        }
        else if (downloadTask.state == NSURLSessionTaskStateRunning)
        {
            // If already downloading, pause the transfer.
            [downloadTask suspend];
            downloading = NO;
        }

    }
}

- (void)downloadAssets
{
    _assets = [self retreiveAssets];    // Getting the resource details from the database
    if (![_assets count])
    {
        // Hide progress
    }
    [self addAssetDownload];
    [self downloadFiles];
}
@end

---

有时它下载第一个文件并停在那里，下一次它不会下载任何东西。直到现在我才发现这个问题，因为这个问题我浪费了将近一天的时间。请帮我找出问题所在。提前感谢。

当使用后台会话时，旧的下载请求可以在会话之间保留。您是否尝试过使用

getTasksWithCompletionHandler

检查旧的、未完成的后台任务？我经历了一段时间，直到我意识到，当我的应用程序启动时，它可能会在旧的后台请求后被积压。如果您在后台会话中有任何无效请求，则可以对所有内容进行一点备份

另外，您的应用程序代理是否正在处理

handleEventsForBackgroundURLSession

方法，重新实例化后台会话并保存传递给您的应用程序的

completionHandler

？您的

NSURLSession

的

委托是否调用该完成处理程序（可能在
urlsessiondifinisheventsforbackgroundurlsession:
方法中）？您要确保清理这些后台会话。我在您的代码片段中没有看到任何这种方法，但为了简洁起见，您可能省略了它

关于这一点的讨论可在《指南》的背景转移注意事项部分找到。WWDC 2013视频播放约40分钟后也显示了这一示例。
使用后台会话时，旧的下载请求可以在会话之间持续。您是否尝试过使用
getTasksWithCompletionHandler
检查旧的、未完成的后台任务？我经历了一段时间，直到我意识到当我的应用程序启动时，它可以