iOS 下载多文件管理

060

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前言

项目自从接入 unity 后，关于资源方面下载数据就增多了，下载种类也变的不一样了。以前手动下载，直接调一下封装好的的 API 就好，也没什么难度，但现在又说什么静默下载，预下载，手动下载，WIFI时候下载，4G网络不下载等等。说白了就是需要做一个下载的优先级管理了。

思路

我们做一个下载，必然有开始，暂停，取消，继续下载，重复下载等等情况，如果有大量的 URL 在同时下载，然后 URL 的状态可能会随时发生变化，那怎么做会比较好控制状态呢。这里提供一个思路，首先弄一个下载队列就设置最大下载数为3个，也就是说并发下载就只有3个，剩下的都放在等待队列当中。一旦有下载完成的，或者失败的，就移除当前的，去等待队列当中随机取出第一个，放到下载队列当中。这样的好处是什么呢，就是我下载的线程永远最多只有3个，这样很容易方便我们去维护状态，这就是我个人思路。

下载管理

现在我们就按照上面的思路去写，首先我们创建一个下载管理的单例 DownloadManager，先添加一个 NSURLSession。

@interface DownloadManager () <NSURLSessionDelegate, NSURLSessionDownloadDelegate>
@property (nonatomic, strong) NSURLSession *session;
// 锁
@property (nonatomic, strong) NSLock *downloadsLock;
// 下载中的队列
@property (nonatomic, strong) NSMutableDictionary *downloads;
// 等待中的队列
@property (nonatomic, strong) NSMutableDictionary *waitDownloads;
// 最大下载数据
@property (nonatomic, assign) NSInteger downloadMaxCount;
@end
@interface DownloadManager () <NSURLSessionDelegate, NSURLSessionDownloadDelegate>
@property (nonatomic, strong) NSURLSession *session;
// 锁
@property (nonatomic, strong) NSLock *downloadsLock;
// 下载中的队列
@property (nonatomic, strong) NSMutableDictionary *downloads;
// 等待中的队列
@property (nonatomic, strong) NSMutableDictionary *waitDownloads;
// 最大下载数据
@property (nonatomic, assign) NSInteger downloadMaxCount;
@end
@interface DownloadManager () <NSURLSessionDelegate, NSURLSessionDownloadDelegate>
@property (nonatomic, strong) NSURLSession *session;
// 锁
@property (nonatomic, strong) NSLock *downloadsLock;
// 下载中的队列
@property (nonatomic, strong) NSMutableDictionary *downloads;
// 等待中的队列
@property (nonatomic, strong) NSMutableDictionary *waitDownloads;
// 最大下载数据
@property (nonatomic, assign) NSInteger downloadMaxCount;
@end

先进行 NSURLSession 初始化，然后添加2个字典，1个为下载中的字典，1个为等待中的字典。

- (instancetype)init
{
    self = [super init];
    if (self)
    {
        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
        self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
        self.downloadsLock = [[NSLock alloc] init];
        self.downloads = [NSMutableDictionary new];
        self.waitDownloads = [NSMutableDictionary new];
        self.downloadMaxCount = 3;
    }
    return self;
}
- (instancetype)init
{


    self = [super init];
    if (self)
    {

        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
        self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
        self.downloadsLock = [[NSLock alloc] init];
        self.downloads = [NSMutableDictionary new];
        self.waitDownloads = [NSMutableDictionary new];
        self.downloadMaxCount = 3;
    }

    return self;
}
- (instancetype)init
{


    self = [super init];
    if (self)
    {

        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
        self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
        self.downloadsLock = [[NSLock alloc] init];
        self.downloads = [NSMutableDictionary new];
        self.waitDownloads = [NSMutableDictionary new];
        self.downloadMaxCount = 3;
    }

    return self;
}

接着我们编写一个下载的方法，记住的是每次获取字典对应的下载对象DownloadObject，添加修改删除等必须添加锁。
这里的一个重点是，如果 urlString 就在我们字典当中，需要覆盖之前的，包括优先级。

- (void)downloadFileForURL:(NSString *)urlString
                  fileName:(NSString *)fileName
                 directory:(NSString *)directory
                  priority:(OPRDownloadPriority)priority
             progressBlock:(void(^)(CGFloat progress))progressBlock
           completionBlock:(void(^)(BOOL completed, NSInteger code))completionBlock {
    // 资源本来就在本地
    if ([self fileExistsWithName:fileName inDirectory:directory])
    {
        completionBlock(YES,0);
        return;
    }
    
    {
        [self.downloadsLock lock];
        // 所有下载队列
        NSMutableDictionary *allDownloads = [self allDownloads];
        DownloadObject *download = [allDownloads objectForKey:urlString];
        [self.downloadsLock unlock];
        if (download)
        {
            // 本来就在队列中
            download.completionBlock = completionBlock;
            download.progressBlock = progressBlock;
            download.priority = priority;
            return;
        }
    }
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
    DownloadObject *downloadObject = [[DownloadObject alloc] initWithDownloadTask:downloadTask
                                                                        progressBlock:progressBlock
                                                                      completionBlock:completionBlock];
    downloadObject.fileName = fileName;
    downloadObject.directoryName = directory;
    downloadObject.priority = priority;
    
    [self.downloadsLock lock];
    //下载队列少于最大下载数量3，则把URLString 添加到队列中，否则放到等待队列
    if (self.downloads.count < self.downloadMaxCount) {
        [self.downloads addEntriesFromDictionary:@{urlString:downloadObject}];
        [downloadTask resume];
    }else {
        [self.waitDownloads addEntriesFromDictionary:@{urlString:downloadObject}];
    }
    [self.downloadsLock unlock];
}
- (void)downloadFileForURL:(NSString *)urlString
                  fileName:(NSString *)fileName
                 directory:(NSString *)directory
                  priority:(OPRDownloadPriority)priority
             progressBlock:(void(^)(CGFloat progress))progressBlock
           completionBlock:(void(^)(BOOL completed, NSInteger code))completionBlock {
    // 资源本来就在本地
    if ([self fileExistsWithName:fileName inDirectory:directory])
    {
        completionBlock(YES,0);
        return;
    }

    
    {
        [self.downloadsLock lock];
        // 所有下载队列
        NSMutableDictionary *allDownloads = [self allDownloads];
        DownloadObject *download = [allDownloads objectForKey:urlString];
        [self.downloadsLock unlock];

        if (download)
        {
            // 本来就在队列中
            download.completionBlock = completionBlock;
            download.progressBlock = progressBlock;
            download.priority = priority;
            return;
        }
    }
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
    DownloadObject *downloadObject = [[DownloadObject alloc] initWithDownloadTask:downloadTask
                                                                        progressBlock:progressBlock
                                                                      completionBlock:completionBlock];
    downloadObject.fileName = fileName;
    downloadObject.directoryName = directory;
    downloadObject.priority = priority;
    
    [self.downloadsLock lock];
    //下载队列少于最大下载数量3，则把URLString 添加到队列中，否则放到等待队列
    if (self.downloads.count < self.downloadMaxCount) {
        [self.downloads addEntriesFromDictionary:@{urlString:downloadObject}];
        [downloadTask resume];
    }else {
        [self.waitDownloads addEntriesFromDictionary:@{urlString:downloadObject}];
    }
    [self.downloadsLock unlock];
}
- (void)downloadFileForURL:(NSString *)urlString
                  fileName:(NSString *)fileName
                 directory:(NSString *)directory
                  priority:(OPRDownloadPriority)priority
             progressBlock:(void(^)(CGFloat progress))progressBlock
           completionBlock:(void(^)(BOOL completed, NSInteger code))completionBlock {
    // 资源本来就在本地
    if ([self fileExistsWithName:fileName inDirectory:directory])
    {
        completionBlock(YES,0);
        return;
    }

    
    {
        [self.downloadsLock lock];
        // 所有下载队列
        NSMutableDictionary *allDownloads = [self allDownloads];
        DownloadObject *download = [allDownloads objectForKey:urlString];
        [self.downloadsLock unlock];

        if (download)
        {
            // 本来就在队列中
            download.completionBlock = completionBlock;
            download.progressBlock = progressBlock;
            download.priority = priority;
            return;
        }
    }
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
    DownloadObject *downloadObject = [[DownloadObject alloc] initWithDownloadTask:downloadTask
                                                                        progressBlock:progressBlock
                                                                      completionBlock:completionBlock];
    downloadObject.fileName = fileName;
    downloadObject.directoryName = directory;
    downloadObject.priority = priority;
    
    [self.downloadsLock lock];
    //下载队列少于最大下载数量3，则把URLString 添加到队列中，否则放到等待队列
    if (self.downloads.count < self.downloadMaxCount) {
        [self.downloads addEntriesFromDictionary:@{urlString:downloadObject}];
        [downloadTask resume];
    }else {
        [self.waitDownloads addEntriesFromDictionary:@{urlString:downloadObject}];
    }
    [self.downloadsLock unlock];
}

我们 NSURLSession 会监听下载状态，第一个是接受服务端返回的数据。这里我们主要是用来监听 URLString的下载进度，我们DownloadObject里面就保存了progressBlock用来返回进度。

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;
    if (!fileIdentifier)
    {
        return;
    }
    
    [self.downloadsLock lock];
    DownloadObject *download = [self.downloads objectForKey:fileIdentifier];
    if (download.progressBlock)
    {
        CGFloat progress = (CGFloat)totalBytesWritten / (CGFloat)totalBytesExpectedToWrite;
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.progressBlock(progress); 
        });
    }
    
    [self.downloadsLock unlock];
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{


    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;

    if (!fileIdentifier)
    {

        return;
    }
    
    [self.downloadsLock lock];
    DownloadObject *download = [self.downloads objectForKey:fileIdentifier];

    if (download.progressBlock)
    {
        CGFloat progress = (CGFloat)totalBytesWritten / (CGFloat)totalBytesExpectedToWrite;
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.progressBlock(progress); 
        });
    }
    
    [self.downloadsLock unlock];
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{


    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;

    if (!fileIdentifier)
    {

        return;
    }
    
    [self.downloadsLock lock];
    DownloadObject *download = [self.downloads objectForKey:fileIdentifier];

    if (download.progressBlock)
    {
        CGFloat progress = (CGFloat)totalBytesWritten / (CGFloat)totalBytesExpectedToWrite;
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.progressBlock(progress); 
        });
    }
    
    [self.downloadsLock unlock];
}

第二个就是下载成功回调。这时候我们首先需要保证我们的目录是存在的，没有就创建一个。
重点是把下载的location，移动到我们的directoryName当中。并且最后需要把 URLString 移出下载队列，然后我们再去等待队列中，看是否有再等待的数据，有就添加到下载队列继续下载。

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{    
    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;
    
    NSURL *destinationLocation;
    // 如果目录没有创建，就创建一个目录
    if (download.directoryName
                 && [self createDirectoryNamed:download.directoryName])
        {
            destinationLocation = [[[self cachesDirectoryUrlPath] URLByAppendingPathComponent:download.directoryName] URLByAppendingPathComponent:download.fileName];
        }
        
        // 把下载的TMP目录移动到我们下载需要保存的目录
        [[NSFileManager defaultManager] moveItemAtURL:location
                                                toURL:destinationLocation
                                                error:&error];
    
    if (download.completionBlock)
    {
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.completionBlock(success,200);
        });
    }
    
    [self.downloads removeObjectForKey:fileIdentifier];
    
    [self addWaitQueueToDownload];
    
    [self.downloadsLock unlock];
  
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{    
    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;

    
    NSURL *destinationLocation;
    // 如果目录没有创建，就创建一个目录
    if (download.directoryName
                 && [self createDirectoryNamed:download.directoryName])
        {
            destinationLocation = [[[self cachesDirectoryUrlPath] URLByAppendingPathComponent:download.directoryName] URLByAppendingPathComponent:download.fileName];
        }
        
        // 把下载的TMP目录移动到我们下载需要保存的目录
        [[NSFileManager defaultManager] moveItemAtURL:location
                                                toURL:destinationLocation
                                                error:&error];
    
    if (download.completionBlock)
    {
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.completionBlock(success,200);
        });
    }
    
    [self.downloads removeObjectForKey:fileIdentifier];
    
    [self addWaitQueueToDownload];
    
    [self.downloadsLock unlock];
  
}
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{    
    NSString *fileIdentifier = downloadTask.originalRequest.URL.absoluteString;

    
    NSURL *destinationLocation;
    // 如果目录没有创建，就创建一个目录
    if (download.directoryName
                 && [self createDirectoryNamed:download.directoryName])
        {
            destinationLocation = [[[self cachesDirectoryUrlPath] URLByAppendingPathComponent:download.directoryName] URLByAppendingPathComponent:download.fileName];
        }
        
        // 把下载的TMP目录移动到我们下载需要保存的目录
        [[NSFileManager defaultManager] moveItemAtURL:location
                                                toURL:destinationLocation
                                                error:&error];
    
    if (download.completionBlock)
    {
        dispatch_async(dispatch_get_main_queue(), ^(void) {
            download.completionBlock(success,200);
        });
    }
    
    [self.downloads removeObjectForKey:fileIdentifier];
    
    [self addWaitQueueToDownload];
    
    [self.downloadsLock unlock];
  
}

最后一个是下载错误。不管是超时还是其它原因，这里都给多一次重试的机会，最后也是通过completionBlock 回调给下载的方法，然后我们再去等待队列中，看是否有再等待的数据，有就添加到下载队列继续下载，这里和下载完成逻辑是一样的。

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    if (error)
    {
        NSString *fileIdentifier = task.originalRequest.URL.absoluteString;
       
        
        BOOL retry = NO;
        if(error.code == NSURLErrorTimedOut)
        {
            retry = YES;
        }
        
        [self.downloadsLock lock];
        DownloadObject *download = [self.downloads objectForKey:fileIdentifier];
        
        if(!retry && !download.hasRetry)
        {
            retry = YES;
            download.hasRetry = YES;
        }
        if(retry)
        {
            // 重试下载
            NSURLRequest *request = [NSURLRequest requestWithURL:task.currentRequest.URL];
            NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
            download.downloadTask = downloadTask;
            [downloadTask resume];
        }
        else
        {
            if (download.completionBlock)
            {
                dispatch_async(dispatch_get_main_queue(), ^(void) {
                    download.completionBlock(NO,error.code);
                });
            }
            
            [self.downloads removeObjectForKey:fileIdentifier];
            
            [self addWaitQueueToDownload];
        }
        
        [self.downloadsLock unlock];
    }
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{


    if (error)
    {
        NSString *fileIdentifier = task.originalRequest.URL.absoluteString;
       
        
        BOOL retry = NO;
        if(error.code == NSURLErrorTimedOut)
        {
            retry = YES;
        }
        
        [self.downloadsLock lock];
        DownloadObject *download = [self.downloads objectForKey:fileIdentifier];
        
        if(!retry && !download.hasRetry)
        {
            retry = YES;
            download.hasRetry = YES;
        }

        if(retry)
        {
            // 重试下载
            NSURLRequest *request = [NSURLRequest requestWithURL:task.currentRequest.URL];
            NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
            download.downloadTask = downloadTask;
            [downloadTask resume];
        }
        else
        {
            if (download.completionBlock)
            {
                dispatch_async(dispatch_get_main_queue(), ^(void) {
                    download.completionBlock(NO,error.code);
                });
            }
            
            [self.downloads removeObjectForKey:fileIdentifier];
            
            [self addWaitQueueToDownload];
        }
        
        [self.downloadsLock unlock];
    }
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{


    if (error)
    {
        NSString *fileIdentifier = task.originalRequest.URL.absoluteString;
       
        
        BOOL retry = NO;
        if(error.code == NSURLErrorTimedOut)
        {
            retry = YES;
        }
        
        [self.downloadsLock lock];
        DownloadObject *download = [self.downloads objectForKey:fileIdentifier];
        
        if(!retry && !download.hasRetry)
        {
            retry = YES;
            download.hasRetry = YES;
        }

        if(retry)
        {
            // 重试下载
            NSURLRequest *request = [NSURLRequest requestWithURL:task.currentRequest.URL];
            NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request];
            download.downloadTask = downloadTask;
            [downloadTask resume];
        }
        else
        {
            if (download.completionBlock)
            {
                dispatch_async(dispatch_get_main_queue(), ^(void) {
                    download.completionBlock(NO,error.code);
                });
            }
            
            [self.downloads removeObjectForKey:fileIdentifier];
            
            [self addWaitQueueToDownload];
        }
        
        [self.downloadsLock unlock];
    }
}

至此，我们下载的实现就基本完成了。我们还需要做的，就是加入取消单个下载方法，暂停单个下载的方法，继续下载单个的下载方法，这些都可以基于上述2个队列进行调整。上述代码有些还不够完整，但对于开发者来说问题不大。

最后

下载文件管理来说，上述的方案其实也是基于现有业务进行调整的，之前是一个下载的队列，现在拆分出2个，然后加了一个自定义的优先级priority,和系统的类似，我们去等待队列中拿数据，也是取出当前优先级最高的，然后添加到下载队列当中。其实也不能说是队列，就是2个字典，说的好听一点而已。对此你觉得有什么更好的方案去做呢，欢迎留意。

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