MCDownloadManager ios文件下載管理器

時間  2019-11-06
標籤 mcdownloadmanager ios 文件 下載 管理器 欄目 iOS 简体版
原文   原文鏈接

咱們用AFNetworking小試牛刀，寫一個簡單的下載器來演示功能。git

前言

爲何AFNetworking可以成爲頂級框架？咱們究竟該如何領悟它的精髓所在？這都是很難的問題。安全，高效，流暢，這3個特性缺一不可。假如咱們要封裝一個通用的網絡框架，提供一個文件下載器是頗有必要的。按照 管理編程原則 ，這個下載管理器應該管理全部的下載任務和依據。github

這是一個簡單的下載器，只爲了功能演示編程

下載器提供的功能

  1. 根據一個url下載文件 咱們下載一個文件，最重要的就是url，所以咱們應該把這個url做爲下載的惟一標識。
  2. 提供下載進度 爲了增長用戶體驗，每每在下載文件的同時，展現一個下載進度告訴用戶當前的下載狀況，有的人喜歡使用bytesWriten/totalBytesWriten/totalExpectedBytesWriten，但AFNetworking中使用的都是NSProgress。所以，咱們也採用NSProgress表示進度。
  3. 下載完成的回調 通知下載完成的方式有通知/代理/Block，咱們採用的是Block。
  4. 下載失敗的回調 同上
  5. 根據url獲取下載對象 咱們把下載的對象包裝成了MCDownloadReceipt，我可以在MCDownloadReceipt對象中獲取到咱們須要的全部內容。
  6. 回覆/暫停/取消 下載任務 這些功能，咱們使用協議來實現。
  7. 下載限制和順序 咱們可以自定義同時下載文件的個數，默認爲4個。可以自定義等待隊列中的任務是先進先出仍是後進先出。

設計思路

寫一個下載器，必定須要一個對象來描述下載的文件。在這個下載器中，咱們使用MCDownloadReceipt。既然是一個信息的載體，那麼從設計角度來講，咱們應該使用它來存儲跟文件相關的內容，不該該讓他完成其餘更多的事情，好比說開始，暫停等等。緩存

MCDownloadReceipt使用歸檔進行本地化存儲。安全

核心下載使用NSURLSession實現，下邊咱們會介紹詳情。網絡

MCDownloadReceipt

MCDownloadReceipt的主要功能是用於記錄下載信息。即便下載未完成，也能在MCDownloadReceipt的filePath路徑下找個這個文件。session

咱們先來看看暴露出來的頭文件信息：app

  • NSString *url 做爲MCDownloadReceipt的惟一標識。
  • NSString *filePath MCDownloadReceipt的文件索引。
  • NSString *filename MCDownloadReceipt的文件名，命名規則爲：把url進行MD5編碼後做爲文件名，url中若是有後綴，就拼接後綴。
  • MCDownloadState state MCDownloadReceipt的狀態
    • MCDownloadStateNone,
    • MCDownloadStateWillResume,
    • MCDownloadStateDownloading,
    • MCDownloadStateSuspened,
    • MCDownloadStateCompleted,
    • MCDownloadStateFailed
  • long long totalBytesWritten 總共寫入的數據的大小
  • totalBytesExpectedToWrite 文件總大小
  • NSOutputStream *stream 用於把數據寫入到路徑中
1.獲取filename

一般咱們把文件的下載URL進行MD5編碼後在拼接上後綴名來做爲本地文件的名稱。框架

把一個字符串轉爲MD5字符串：less

static NSString * getMD5String(NSString *str) {
    
    if (str == nil) return nil;
    
    const char *cstring = str.UTF8String;
    unsigned char bytes[CC_MD5_DIGEST_LENGTH];
    CC_MD5(cstring, (CC_LONG)strlen(cstring), bytes);
    
    NSMutableString *md5String = [NSMutableString string];
    for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
        [md5String appendFormat:@"%02x", bytes[i]];
    }
    return md5String;
}

拼接名稱：

- (NSString *)filename {
    if (_filename == nil) {
        NSString *pathExtension = self.url.pathExtension;
        if (pathExtension.length) {
            _filename = [NSString stringWithFormat:@"%@.%@", getMD5String(self.url), pathExtension];
        } else {
            _filename = getMD5String(self.url);
        }
    }
    return _filename;
}
2.獲取filePath

首先咱們要獲取一個緩存的路徑：

NSString * const MCDownloadCacheFolderName = @"MCDownloadCache";

static NSString * cacheFolder() {
    NSFileManager *filemgr = [NSFileManager defaultManager];
    static NSString *cacheFolder;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (!cacheFolder) {
            NSString *cacheDir = NSHomeDirectory();
            cacheFolder = [cacheDir stringByAppendingPathComponent:MCDownloadCacheFolderName];
        }
        NSError *error = nil;
        if(![filemgr createDirectoryAtPath:cacheFolder withIntermediateDirectories:YES attributes:nil error:&error]) {
            NSLog(@"Failed to create cache directory at %@", cacheFolder);
            cacheFolder = nil;
        }
    });
    
    return cacheFolder;
}

拼接路徑和文件名：

- (NSString *)filePath {

    NSString *path = [cacheFolder() stringByAppendingPathComponent:self.filename];
    if (![path isEqualToString:_filePath] ) {
        if (_filePath && ![[NSFileManager defaultManager] fileExistsAtPath:_filePath]) {
            NSString *dir = [_filePath stringByDeletingLastPathComponent];
            [[NSFileManager defaultManager] createDirectoryAtPath:dir withIntermediateDirectories:YES attributes:nil error:nil];
        }
        _filePath = path;
    }
    
    return _filePath;
}
3.獲取文件的大小

獲取某個路徑下文件的大小：

static unsigned long long fileSizeForPath(NSString *path) {
    
    signed long long fileSize = 0;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:path]) {
        NSError *error = nil;
        NSDictionary *fileDict = [fileManager attributesOfItemAtPath:path error:&error];
        if (!error && fileDict) {
            fileSize = [fileDict fileSize];
        }
    }
    return fileSize;
}

獲取本對象的文件大小：

- (long long)totalBytesWritten {
    
    return fileSizeForPath(self.filePath);
}
4.初始化stream
- (NSOutputStream *)stream
{
    if (_stream == nil) {
        _stream = [NSOutputStream outputStreamToFileAtPath:self.filePath append:YES];
    }
    return _stream;
}
5.設置progress
- (NSProgress *)progress {
    if (_progress == nil) {
        _progress = [[NSProgress alloc] initWithParent:nil userInfo:nil];
    }
    _progress.totalUnitCount = self.totalBytesExpectedToWrite;
    _progress.completedUnitCount = self.totalBytesWritten;
    return _progress;
}
6.初始化和歸檔
- (instancetype)initWithURL:(NSString *)url {
    if (self = [self init]) {
   
        self.url = url;
        self.totalBytesExpectedToWrite = 1;
    }
    return self;
}

#pragma mark - NSCoding
- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:self.url forKey:NSStringFromSelector(@selector(url))];
    [aCoder encodeObject:self.filePath forKey:NSStringFromSelector(@selector(filePath))];
    [aCoder encodeObject:@(self.state) forKey:NSStringFromSelector(@selector(state))];
    [aCoder encodeObject:self.filename forKey:NSStringFromSelector(@selector(filename))];
    [aCoder encodeObject:@(self.totalBytesWritten) forKey:NSStringFromSelector(@selector(totalBytesWritten))];
    [aCoder encodeObject:@(self.totalBytesExpectedToWrite) forKey:NSStringFromSelector(@selector(totalBytesExpectedToWrite))];

}

- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super init];
    if (self) {
        self.url = [aDecoder decodeObjectForKey:NSStringFromSelector(@selector(url))];
        self.filePath = [aDecoder decodeObjectForKey:NSStringFromSelector(@selector(filePath))];
        self.state = [[aDecoder decodeObjectOfClass:[NSNumber class] forKey:NSStringFromSelector(@selector(state))] unsignedIntegerValue];
        self.filename = [aDecoder decodeObjectForKey:NSStringFromSelector(@selector(filename))];
        self.totalBytesWritten = [[aDecoder decodeObjectOfClass:[NSNumber class] forKey:NSStringFromSelector(@selector(totalBytesWritten))] unsignedIntegerValue];
        self.totalBytesExpectedToWrite = [[aDecoder decodeObjectOfClass:[NSNumber class] forKey:NSStringFromSelector(@selector(totalBytesExpectedToWrite))] unsignedIntegerValue];

    }
    return self;
}

MCDownloadControlDelegate

是這樣的，若是咱們要給某個對象擴展一類的功能或者方法，那麼咱們最好使用協議。在AFNetworking的AFURLResponseSerialization和AFURLRequestSerialization就是最好的例子。

@protocol MCDownloadControlDelegate <NSObject>

- (void)resumeWithURL:(NSString * _Nonnull)url;
- (void)resumeWithDownloadReceipt:(MCDownloadReceipt * _Nonnull)receipt;

- (void)suspendWithURL:(NSString * _Nonnull)url;
- (void)suspendWithDownloadReceipt:(MCDownloadReceipt * _Nonnull)receipt;

- (void)removeWithURL:(NSString * _Nonnull)url;
- (void)removeWithDownloadReceipt:(MCDownloadReceipt * _Nonnull)receipt;

@end

實現部分：

#pragma mark - MCDownloadControlDelegate

- (void)resumeWithURL:(NSString *)url {
    
    if (url == nil) return;
    
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:url];
    [self resumeWithDownloadReceipt:receipt];
    
}
- (void)resumeWithDownloadReceipt:(MCDownloadReceipt *)receipt {
    
    if ([self isActiveRequestCountBelowMaximumLimit]) {
        [self startTask:self.tasks[receipt.url]];
    }else {
        receipt.state = MCDownloadStateWillResume;
        [self saveReceipts:self.allDownloadReceipts];
        [self enqueueTask:self.tasks[receipt.url]];
    }
}

- (void)suspendAll {
    
    for (NSURLSessionDownloadTask *task in self.queuedTasks) {
        [task suspend];
        MCDownloadReceipt *receipt = [self downloadReceiptForURL:task.taskDescription];
        receipt.state = MCDownloadStateSuspened;
    }

    [self saveReceipts:self.allDownloadReceipts];
    
}
-(void)suspendWithURL:(NSString *)url {
    
     if (url == nil) return;
    
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:url];
    [self suspendWithDownloadReceipt:receipt];
    
}
- (void)suspendWithDownloadReceipt:(MCDownloadReceipt *)receipt {
    
    [self updateReceiptWithURL:receipt.url state:MCDownloadStateSuspened];
    NSURLSessionDataTask *task = self.tasks[receipt.url];
    if (task) {
        [task suspend];
    }
}


- (void)removeWithURL:(NSString *)url {
    
    if (url == nil) return;
    
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:url];
    [self removeWithDownloadReceipt:receipt];
    
}
- (void)removeWithDownloadReceipt:(MCDownloadReceipt *)receipt {
    
    NSURLSessionDataTask *task = self.tasks[receipt.url];
    if (task) {
        [task cancel];
    }
    
    [self.queuedTasks removeObject:task];
    [self safelyRemoveTaskWithURLIdentifier:receipt.url];
    
    [self.allDownloadReceipts removeObject:receipt];
    
    [self saveReceipts:self.allDownloadReceipts];
    
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager removeItemAtPath:receipt.filePath error:nil];

}

MCDownloadManager

初始化MCDownloadManager跟AFNetworking中AFImageDownloader的初始化很像，作一些網絡配置。參數配置。咱們規定下載任務的建立都放在一個專有的同步隊列中完成。咱們還要監聽applicationWillTerminate 和 applicationDidReceiveMemoryWarning這兩個通知，並在通知方法中，暫停多有的下載任務。

初始化示例代碼：

+ (NSURLSessionConfiguration *)defaultURLSessionConfiguration {
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    
    configuration.HTTPShouldSetCookies = YES;
    configuration.HTTPShouldUsePipelining = NO;
    configuration.requestCachePolicy = NSURLRequestUseProtocolCachePolicy;
    configuration.allowsCellularAccess = YES;
    configuration.timeoutIntervalForRequest = 60.0;
   
    return configuration;
}


- (instancetype)init {
    

    NSURLSessionConfiguration *defaultConfiguration = [self.class defaultURLSessionConfiguration];
  
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 1;
    NSURLSession *session = [NSURLSession sessionWithConfiguration:defaultConfiguration delegate:self delegateQueue:queue];
    
    return [self initWithSession:session
                 downloadPrioritization:MCDownloadPrioritizationFIFO
                 maximumActiveDownloads:4 ];
}


- (instancetype)initWithSession:(NSURLSession *)session downloadPrioritization:(MCDownloadPrioritization)downloadPrioritization maximumActiveDownloads:(NSInteger)maximumActiveDownloads {
    if (self = [super init]) {
        
        self.session = session;
        self.downloadPrioritizaton = downloadPrioritization;
        self.maximumActiveDownloads = maximumActiveDownloads;
        
        self.queuedTasks = [[NSMutableArray alloc] init];
        self.tasks = [[NSMutableDictionary alloc] init];
        self.activeRequestCount = 0;
        

        NSString *name = [NSString stringWithFormat:@"com.mc.downloadManager.synchronizationqueue-%@", [[NSUUID UUID] UUIDString]];
        self.synchronizationQueue = dispatch_queue_create([name cStringUsingEncoding:NSASCIIStringEncoding], DISPATCH_QUEUE_SERIAL);

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationWillTerminate:) name:UIApplicationWillTerminateNotification object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationDidReceiveMemoryWarning:) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
        
    }
    
    return self;
}

+ (instancetype)defaultInstance {
    static MCDownloadManager *sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] init];
    });
    return sharedInstance;
}

初始化完成後，咱們須要在MCDownloadManager中拿到全部的下載的數據，以及可以保存這些數據到本地。

示例代碼：

- (NSMutableArray *)allDownloadReceipts {
    if (_allDownloadReceipts == nil) {
         NSArray *receipts = [NSKeyedUnarchiver unarchiveObjectWithFile:LocalReceiptsPath()];
        _allDownloadReceipts = receipts != nil ? receipts.mutableCopy : [NSMutableArray array];
    }
    return _allDownloadReceipts;
}

- (void)saveReceipts:(NSArray <MCDownloadReceipt *>*)receipts {
    [NSKeyedArchiver archiveRootObject:receipts toFile:LocalReceiptsPath()];
}

下載的核心方法：

- (MCDownloadReceipt *)downloadFileWithURL:(NSString *)url
                                         progress:(void (^)(NSProgress * _Nonnull,MCDownloadReceipt *receipt))downloadProgressBlock
                                         destination:(NSURL *  (^)(NSURL * _Nonnull, NSURLResponse * _Nonnull))destination
                                          success:(nullable void (^)(NSURLRequest * _Nullable, NSHTTPURLResponse * _Nullable, NSURL * _Nonnull))success
                                          failure:(nullable void (^)(NSURLRequest * _Nullable, NSHTTPURLResponse * _Nullable, NSError * _Nonnull))failure {
 
   __block MCDownloadReceipt *receipt = [self downloadReceiptForURL:url];
    
    dispatch_sync(self.synchronizationQueue, ^{
        NSString *URLIdentifier = url;
        if (URLIdentifier == nil) {
            if (failure) {
                NSError *error = [NSError errorWithDomain:NSURLErrorDomain code:NSURLErrorBadURL userInfo:nil];
                dispatch_async(dispatch_get_main_queue(), ^{
                    failure(nil, nil, error);
                });
            }
            return;
        }

        receipt.successBlock = success;
        receipt.failureBlock = failure;
        receipt.progressBlock = downloadProgressBlock;
        
        if (receipt.state == MCDownloadStateCompleted) {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (receipt.successBlock) {
                    receipt.successBlock(nil,nil,[NSURL URLWithString:receipt.url]);
                }
            });
            return ;
        }
        
        if (receipt.state == MCDownloadStateDownloading) {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (receipt.progressBlock) {
                    receipt.progressBlock(receipt.progress,receipt);
                }
            });
            return ;
        }

        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:receipt.url]];
        NSString *range = [NSString stringWithFormat:@"bytes=%zd-", receipt.totalBytesWritten];
        [request setValue:range forHTTPHeaderField:@"Range"];
        
        NSURLSessionDataTask *task = [self.session dataTaskWithRequest:request];
        task.taskDescription = receipt.url;
        self.tasks[receipt.url] = task;
        [self.queuedTasks addObject:task];
        
        [self resumeWithURL:receipt.url];
        
        
        });
    return receipt;
}

--

- (NSURLSessionDownloadTask*)safelyRemoveTaskWithURLIdentifier:(NSString *)URLIdentifier {
    __block NSURLSessionDownloadTask *task = nil;
    dispatch_sync(self.synchronizationQueue, ^{
        task = [self removeTaskWithURLIdentifier:URLIdentifier];
    });
    return task;
}

//This method should only be called from safely within the synchronizationQueue
- (NSURLSessionDownloadTask *)removeTaskWithURLIdentifier:(NSString *)URLIdentifier {
    NSURLSessionDownloadTask *task = self.tasks[URLIdentifier];
    [self.tasks removeObjectForKey:URLIdentifier];
    return task;
}

- (void)safelyDecrementActiveTaskCount {
    dispatch_sync(self.synchronizationQueue, ^{
        if (self.activeRequestCount > 0) {
            self.activeRequestCount -= 1;
        }
    });
}

- (void)safelyStartNextTaskIfNecessary {
    dispatch_sync(self.synchronizationQueue, ^{
        if ([self isActiveRequestCountBelowMaximumLimit]) {
            while (self.queuedTasks.count > 0) {
                NSURLSessionDownloadTask *task = [self dequeueTask];
                MCDownloadReceipt *receipt = [self downloadReceiptForURL:task.taskDescription];
                if (task.state == NSURLSessionTaskStateSuspended && receipt.state == MCDownloadStateWillResume) {
                    [self startTask:task];
                    break;
                }
            }
        }
    });
}


- (void)startTask:(NSURLSessionDownloadTask *)task {
    [task resume];
    ++self.activeRequestCount;
    [self updateReceiptWithURL:task.taskDescription state:MCDownloadStateDownloading];
}

- (void)enqueueTask:(NSURLSessionDownloadTask *)task {
    switch (self.downloadPrioritizaton) {
        case MCDownloadPrioritizationFIFO:  //
            [self.queuedTasks addObject:task];
            break;
        case MCDownloadPrioritizationLIFO:  //
            [self.queuedTasks insertObject:task atIndex:0];
            break;
    }
}

- (NSURLSessionDownloadTask *)dequeueTask {
    NSURLSessionDownloadTask *task = nil;
    task = [self.queuedTasks firstObject];
    [self.queuedTasks removeObject:task];
    return task;
}

- (BOOL)isActiveRequestCountBelowMaximumLimit {
    return self.activeRequestCount < self.maximumActiveDownloads;
}

根據URL獲取receipt對象：

- (MCDownloadReceipt *)downloadReceiptForURL:(NSString *)url {
    
    if (url == nil) return nil;
    for (MCDownloadReceipt *receipt in self.allDownloadReceipts) {
        if ([receipt.url isEqualToString:url]) {
            return receipt;
        }
    }
    MCDownloadReceipt *receipt = [[MCDownloadReceipt alloc] initWithURL:url];
    receipt.state = MCDownloadStateNone;
    receipt.totalBytesExpectedToWrite = 1;
    [self.allDownloadReceipts addObject:receipt];
    [self saveReceipts:self.allDownloadReceipts];
    return receipt;
}

NSURLSessionDataDelegate：

在接到響應後,保存totalBytesExpectedToWrite和state

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:dataTask.taskDescription];
    receipt.totalBytesExpectedToWrite = dataTask.countOfBytesExpectedToReceive;
    receipt.state = MCDownloadStateDownloading;
    @synchronized (self) {
        [self saveReceipts:self.allDownloadReceipts];
    }
   
    [receipt.stream open];
    
    completionHandler(NSURLSessionResponseAllow);
}

在接收到數據後，寫入文件而且調用progressBlock

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:dataTask.taskDescription];
    
    [receipt.stream write:data.bytes maxLength:data.length];

    receipt.progress.totalUnitCount = receipt.totalBytesExpectedToWrite;
    receipt.progress.completedUnitCount = receipt.totalBytesWritten;
   dispatch_async(dispatch_get_main_queue(), ^{
       if (receipt.progressBlock) {
           receipt.progressBlock(receipt.progress,receipt);
       }
   });

}

下載完成後

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    MCDownloadReceipt *receipt = [self downloadReceiptForURL:task.taskDescription];
    [receipt.stream close];
    receipt.stream = nil;

    if (error) {
        receipt.state = MCDownloadStateFailed;
        dispatch_async(dispatch_get_main_queue(), ^{
            if (receipt.failureBlock) {
                receipt.failureBlock(task.originalRequest,(NSHTTPURLResponse *)task.response,error);
            }
        });
    }else {
        receipt.state = MCDownloadStateCompleted;
        dispatch_async(dispatch_get_main_queue(), ^{
            if (receipt.successBlock) {
                receipt.successBlock(task.originalRequest,(NSHTTPURLResponse *)task.response,task.originalRequest.URL);
            }
        });
    }
    @synchronized (self) {
        [self saveReceipts:self.allDownloadReceipts];
    }
    [self safelyDecrementActiveTaskCount];
    [self safelyStartNextTaskIfNecessary];
    
}

總結

這個下載器就介紹到這裏了，能夠在https://github.com/agelessman/MCDownloadManager.git下載demo。如發現任何問題或改進意見，能夠留言，我會盡力完成。

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