AFN多文件进度下载

AFN参考资料

http://www.jianshu.com/p/c36159094e24

http://blog.cnbang.net/tech/2320/
http://blog.cnbang.net/tech/2371/
http://blog.cnbang.net/tech/2416/
http://www.ruanyifeng.com/blog/2013/06/rsa_algorithm_part_one.html
http://www.ruanyifeng.com/blog/2013/07/rsa_algorithm_part_two.html
http://bugly.qq.com/bbs/forum.php?
http://www.guokr.com/post/114121/mod=viewthread&tid=417&fromuid=6
http://www.guokr.com/post/116169/
http://www.guokr.com/blog/148613/
http://www.cnblogs.com/hyddd/archive/2009/01/07/1371292.html
http://www.cnblogs.com/polobymulberry/p/5140806.html
https://github.com/AFNetworking/AFNetworking/tree/3.1.0

作者：要上班的斌哥
链接：http://www.jianshu.com/p/c36159094e24
來源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

最近在写的一个项目里面涉及到资源包的下载操作，由于用户在使用过程中有可能会同时下载多个资源包，那么就需要对下载功能进行设计和封装。最开始使用的是使用AFN的下载方法来进行实现的，不过当时项目需求要求不是太高，所以没有处理一些特殊情况，比如任务数量的控制，优先级还有断点下载等等。就简单的在一个单例Manager里面添加了一个字典，将下载资源包的URL地址作为Key，对应的downloadTask作为Value，这样就可以在想要的地方获取到相应的下载进度了。

@property (nonatomic, strong, nonnull) NSMutableDictionary <NSString *, NSURLSessionDownloadTask *> *downloadTaskDict;

由于现在需要统一管理下载的资源，而且为了表示“用户至上”，比如节约流量需要使用断点下载，包括暂停和继续、应用重启时的断点下载；显示下载速度和比例等等。同时为了控制下载的速度也对最大下载数量进行了限制，默认3个等等。so.....

先说下原理

这里使用了AFN的下载方法来完成下载功能，只不过需要对其进行一些扩展。因此我将每个下载任务封装成了一个模型<FKNetworkingDownloadModel>,以下为部分属性定义：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

NS_CLASS_AVAILABLE_IOS(7_0) @interface FKNetworkingProgressModel : NSObject 

/*
 * data length of the bytes written.
 */
@property (nonatomic, assign) int64_t totalBytesWritten;
/*
 * the total bytes of the resource data.
 */
@property (nonatomic, assign) int64_t totalBytesExpectedToWrite;
/*
 * download speed.
 */
@property (nonatomic, assign) int64_t downloadSpeed;
/*
 * download progress.
 */
@property (nonatomic, assign) float downloadProgress;
/*
 * download left time
 */
@property (nonatomic, assign) int32_t downloadLeft;

@end

NS_CLASS_AVAILABLE_IOS(7_0) @interface FKNetworkingDownloadModel : NSObject

/*
 * resource URLString 
 */
@property (nonatomic, copy) NSString *resourceURLString;
/*
 * fileName default is resourceURLString last component
 */
@property (nonatomic, copy) NSString *fileName;
/**
 *  file directory
 */
@property (nonatomic, copy) NSString *fileDirectory;
/**
 *  file path
 */
@property (nonatomic, copy, nullable) NSString *filePath;
/**
 *  the plist file path, the plist file include information of the download task mission.
 */
@property (nonatomic, copy, nullable) NSString *plistFilePath;
/**
 *  record the download time when receive the data from the serverce, used to calculate download speed
 */
@property (nonatomic, strong) NSDate *downloadDate;
/**
 *  check the download state when a model alloc. 
 */
//@property (nonatomic, assign) FKDownloadModelState modelState;
/**
 *  resume data, marked the position of the download mission.
 */
@property (nonatomic, strong, nullable) NSData *resumeData;
/*
 * download task
 */
@property (nonatomic, strong, nullable) NSURLSessionDownloadTask *downloadTask;
/*
 * progress
 */
@property (nonatomic, strong, nullable) FKNetworkingProgressModel *progressModel;
/**
 *  init method
 *
 *  @param URLString resourceURLString
 *
 *  @return 
 */
-(instancetype)initWithResourceURLString:(NSString *)URLString;

@end

NS_ASSUME_NONNULL_END

这样可以将每一个下载的资源封装成一个Model，这样在使用管理类来控制下载的时候就会显得比较轻松。

在使用AFN之前需要补充说明一下NSURLSessionTask的一些知识：
抽象类（父类）：NSURLSessionTask 包含了一些属性,其中使用到的属性包括：

//请求信息，包括URL地址等。
@property (nullable, readonly, copy) NSURLRequest  *originalRequest; 
@property (nullable, readonly, copy) NSURLRequest  *currentRequest;  
//响应信息，包括响应数据的长度和地址等等
@property (nullable, readonly, copy) NSURLResponse *response;     
//下面两个属性是会使用到的，一个是已经接收到的数据长度和总共需要接受的数据长度，根据这个我们可以算出下载的进度信息   
@property (readonly) int64_t countOfBytesReceived;
@property (readonly) int64_t countOfBytesExpectedToReceive;
//任务描述，我这里用model对应的URL地址来赋值
@property (nullable, copy) NSString *taskDescription;
//状态（取消、完成、进行中等）
@property (readonly) NSURLSessionTaskState state;

同时父类也提供了几个方法

- (void)cancel;//取消下载任务
- (void)suspend;//挂起(这个一般用于程序在运行中的时候暂停下载任务)
- (void)resume;//恢复下载任务

理论上说，如果不做应用重启后的断点下载，通过上面的步骤已经可以完成大部分的下载操作了，但是在程序重启时并不能够获取到对应的已下载的进度（downloadTask会将下载的资源放入tmp路径下面，以'CFNetworking'开头），那这个时候执行下载任务那么会重新下载。考虑到用户的流量，就必须在重启后的进行断点下载，因此我们需要使用到子类NSURLSessionDownloadTask的一个方法

- (void)cancelByProducingResumeData:(void (^)(NSData * __nullable resumeData))completionHandler;

这个方法可以讲当前的task已下载的数据使用一个data保存起来, 然后使用NSURLSession的方法可以根据这个data从服务器获取后续的数据

- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;

断点下载的原理大概就是这样，接下来是考虑管理类的设计和封装。

管理类的设计和封装

思路：使用单例来管理下载任务，同时可以指定最大的下载数和单任务和多任务模式的切换。关于下载的控制(开始、暂停、恢复和断点下载)都可以通过AFN相应的方法来实现

ANF里面关于下载有几个方法，在<AFURLSessionManager>类里面可以找到
//这个方法是经常用到的一个，生成一个NSURLRequest，然后根据这个请求开始下载任务可以追踪到下载的进度，需要设置下载完成后的文件移动到的位置，最后是完成后的回调信息
-(NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
                                             progress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                                          destination:(nullable NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
                                    completionHandler:(nullable void (^)(NSURLResponse *response, NSURL * _Nullable filePath, NSError * _Nullable error))completionHandler;

//该方法根据一个resumeData来进行断点下载，我这里断点下载的实现就是根据这个来的，resumeData已经在模型里面了。
在下载cancel或者suspend的时候只需要将model的resumeData赋值，然后写入本地plist文件，下次下载的时候根据plist信息获取下载的一些信息就OK了
-(NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData
                                                progress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                                             destination:(nullable NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
                                       completionHandler:(nullable void (^)(NSURLResponse *response, NSURL * _Nullable filePath, NSError * _Nullable error))completionHandler;

下面附上一头文件中的一些代码

#import <Foundation/Foundation.h>
#import "AFNetworking.h"
#import "FKNetworkingDownloadModel.h"

NS_ASSUME_NONNULL_BEGIN

NS_CLASS_AVAILABLE_IOS(7_0) @interface FKNetworkingManager : NSObject

/**
 *  download root file path. default is '~/cache/forkid.networking.manager1.0'
 */
@property (nonatomic, copy, readonly) NSString *downloadDirectory;

/**
 *  contains the models whose is downloading.   
 */
@property (nonatomic, strong, readonly) NSMutableArray <__kindof FKNetworkingDownloadModel *> *downloadingModels;

/**
 *  contains the models whose is waiting for download.   
 */
@property (nonatomic, strong, readonly) NSMutableArray <__kindof FKNetworkingDownloadModel *> *waitingModels;

/**
 *  max download mission number.
 */
@property (nonatomic, assign) NSInteger maxDownloadCount;

/**
 *  first in and fisrt out. 
 */
@property (nonatomic, assign) BOOL resumeTaskFIFO;

/**
 *  ignore maxDownloadCount. manager will resume all downloadTask.
 */
@property (nonatomic, assign, getter=isBatchDownload) BOOL batchDownload;

/**
  *  singleton
  */
+(FKNetworkingManager *)shareManager;

/**
 ===============> Description of download start <=============
 = when you wanna download a file from serverce, you can use next methods as you need. 
 = there have some methods such as start, resume, cancel and so on.
 = We add the 'cancel' method to pause a task instead of suspend, because we need to resume the task when the App restart.
 = all methods will use a download model who is subclass of the 'FKNetworkingDownloadModel' for convenience. 
 = and every model use a URL string as the primary key to mark a download mission or task.
 ===============> Description of download end. <=============
 */

/**
 *  this method used to start a download mission with a download model, notice that the download model can't be nil, or the download mission will not execute.
 *
 *  @param downloadModel     download model
 *  @param progress          progress of the download, track to refresh UI and ...
 *  @param completionHandler you can doing something after download mission completed, such as refresh your UI and move the file and so on.
 */
-(void)fk_startDownloadWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel 
                                progress:(void (^)(FKNetworkingDownloadModel *downloadModel))progress
                       completionHandler:(void (^)(FKNetworkingDownloadModel *downloadModel, NSError * _Nullable error))completionHandler;

/**
 *  resume a download task with a download model, it will use the download model's 'resumeData'
 *
 *  @param downloadModel download model 
 */
-(void)fk_resumeDownloadWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel;                          

/**
 *  suspend or cancel a download task
 *
 *  @param downloadModel download model
 */
-(void)fk_cancelDownloadTaskWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel;

/**
 *  check the resourece has been downloaded or not from the download model resourceURL.
 *
 *  @param downloadModel download model
 *
 *  @return YES or NO.
 */
-(BOOL)fk_hasDownloadedFileWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel; 

/**
 *  delete local file if exist.
 *
 *  @param downloadModel download model.
 */
-(void)fk_deleteDownloadedFileWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel;

/**
 *  delete all downloaded files.
 */
-(void)fk_deleteAllDownloadedFiles;

/**
 *  get a download model, which is downloading with a URLString. if there is not exist a model, will return nil.
 *
 *  @param URLString URLString.
 *
 *  @return download model
 */
-(nullable FKNetworkingDownloadModel *)fk_getDownloadingModelWithURLString:(NSString *)URLString;

/**
 *  get download progress information. such as download speed, progress and so on.
 *
 *  @param downloadModel download model.
 *
 *  @return progress model.
 */
-(nullable FKNetworkingProgressModel *)fk_getDownloadProgressModelWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel;
@end
NS_ASSUME_NONNULL_END

定义完上述的方法后，在实现文件中实现相应的方法即可，因为采用AFN，所以我们不用写太多的步骤，只需要关心流程控制，和线程控制就行了。

下面是部分的实现代码：

#import "FKNetworkingManager.h"
#import "NSObject+FKAdd.h"

NSString *const FKNetworkingManagerFileName = @"forkid.networking.manager1.0";

@interface FKNetworkingManager ()

/**
 *  AFNetworking manager.
 */
@property (nonatomic, strong) AFHTTPSessionManager *AFManager;

/**
 *  download root directory.
 */
@property (nonatomic, copy) NSString *downloadDirectory;

/**
 *  fileManager to manage download files
 */
@property (nonatomic, strong) NSFileManager *fileManager;

/*
 * the models for waiting for download, the elements should be FKDownloadModel and it's subClasses
 */
@property (nonatomic, strong) NSMutableArray <__kindof FKNetworkingDownloadModel *> *waitingModels;

/*
 * the models whose being downloaded, the elements should be FKDownloadModel and it's subClasses
 */
@property (nonatomic, strong) NSMutableArray <__kindof FKNetworkingDownloadModel *> *downloadingModels;

/*
 *  key-values dictionary of the downloadModels, format as '<NSString *key, FKDownloadModel *model>' to make constraints
 *  used to find a downloadModel from this container, 
 *  when the program will terminate, container will be clear
 */
@property (nonatomic, strong) NSMutableDictionary <NSString *, __kindof FKNetworkingDownloadModel *> *downloadModelsDict;

@end

NSInteger const fk_timeInterval = 5;

@implementation FKNetworkingManager

#pragma mark - download methods

-(void)fk_startDownloadWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel 
                                progress:(void (^)(FKNetworkingDownloadModel * _Nonnull))progress 
                       completionHandler:(void (^)(FKNetworkingDownloadModel * _Nonnull, NSError * _Nullable))completionHandler{

    NSString *fileName = [downloadModel.fileName componentsSeparatedByString:@"."].firstObject;
    downloadModel.fileDirectory = [self.downloadDirectory stringByAppendingPathComponent:fileName];
    downloadModel.filePath = [[self.downloadDirectory stringByAppendingPathComponent:fileName] stringByAppendingPathComponent:downloadModel.fileName];
    downloadModel.plistFilePath = [downloadModel.fileDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.plist", fileName]];

    if (![self canBeStartDownloadTaskWithDownloadModel:downloadModel]) return;

    downloadModel.resumeData = [NSData dataWithContentsOfFile:downloadModel.plistFilePath];

    if (downloadModel.resumeData.length == 0) {
        NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:downloadModel.resourceURLString]];
        downloadModel.downloadTask = [self.AFManager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {

            [self setValuesForDownloadModel:downloadModel withProgress:downloadProgress.fractionCompleted];
            progress(downloadModel);

        } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {

            return [NSURL fileURLWithPath:downloadModel.filePath];

        } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
            if (error) {
                [self fk_cancelDownloadTaskWithDownloadModel:downloadModel];
                completionHandler(downloadModel, error);
            }else{
                [self.downloadModelsDict removeObjectForKey:downloadModel.resourceURLString];
                completionHandler(downloadModel, nil);
                [self deletePlistFileWithDownloadModel:downloadModel];
            }
        }];

    }else{

        downloadModel.progressModel.totalBytesWritten = [self getResumeByteWithDownloadModel:downloadModel];
        downloadModel.downloadTask = [self.AFManager downloadTaskWithResumeData:downloadModel.resumeData progress:^(NSProgress * _Nonnull downloadProgress) {

            [self setValuesForDownloadModel:downloadModel withProgress:[self.AFManager downloadProgressForTask:downloadModel.downloadTask].fractionCompleted];
            progress(downloadModel);

        } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
            return [NSURL fileURLWithPath:downloadModel.filePath];
        } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
            if (error) {
                [self fk_cancelDownloadTaskWithDownloadModel:downloadModel];
                completionHandler(downloadModel, error);
            }else{
                [self.downloadModelsDict removeObjectForKey:downloadModel.resourceURLString];
                completionHandler(downloadModel, nil);
                [self deletePlistFileWithDownloadModel:downloadModel];
            }
        }];
    }

    if (![self.fileManager fileExistsAtPath:self.downloadDirectory]) {
        [self.fileManager createDirectoryAtPath:self.downloadDirectory withIntermediateDirectories:YES attributes:nil error:nil];
    }

    [self createFolderAtPath:[self.downloadDirectory stringByAppendingPathComponent:fileName]];
    [self fk_resumeDownloadWithDownloadModel:downloadModel];
}

-(void)fk_resumeDownloadWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if (downloadModel.downloadTask) {
        downloadModel.downloadDate = [NSDate date];
        [downloadModel.downloadTask resume];
        self.downloadModelsDict[downloadModel.resourceURLString] = downloadModel;
        [self.downloadingModels addObject:downloadModel];
    }
}

-(void)fk_cancelDownloadTaskWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if (!downloadModel) return;
    NSURLSessionTaskState state = downloadModel.downloadTask.state;
    if (state == NSURLSessionTaskStateRunning) {
        [downloadModel.downloadTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
            downloadModel.resumeData = resumeData;
            @synchronized (self) {
                BOOL isSuc = [downloadModel.resumeData writeToFile:downloadModel.plistFilePath atomically:YES];
                [self saveTotalBytesExpectedToWriteWithDownloadModel:downloadModel];
                if (isSuc) {
                    downloadModel.resumeData = nil;
                    [self.downloadModelsDict removeObjectForKey:downloadModel.resourceURLString];
                    [self.downloadingModels removeObject:downloadModel];
                }
            }
        }];
    }
}

-(void)fk_deleteDownloadedFileWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if ([self.fileManager fileExistsAtPath:downloadModel.fileDirectory]) {
        [self.fileManager removeItemAtPath:downloadModel.fileDirectory error:nil];
    }
}

-(void)fk_deleteAllDownloadedFiles{
    if ([self.fileManager fileExistsAtPath:self.downloadDirectory]) {
        [self.fileManager removeItemAtPath:self.downloadDirectory error:nil];
    }
}

-(BOOL)fk_hasDownloadedFileWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if ([self.fileManager fileExistsAtPath:downloadModel.filePath]) {
        NSLog(@"已下载的文件...");
        return YES;
    }
    return NO;
}

-(FKNetworkingDownloadModel *)fk_getDownloadingModelWithURLString:(NSString *)URLString{
    return self.downloadModelsDict[URLString];
}

-(FKNetworkingProgressModel *)fk_getDownloadProgressModelWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    FKNetworkingProgressModel *progressModel = downloadModel.progressModel;
    progressModel.downloadProgress = [self.AFManager downloadProgressForTask:downloadModel.downloadTask].fractionCompleted;
    return progressModel;
}

#pragma mark - private methods
-(BOOL)canBeStartDownloadTaskWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if (!downloadModel) return NO;
    if (downloadModel.downloadTask && downloadModel.downloadTask.state == NSURLSessionTaskStateRunning) return NO;
    if ([self fk_hasDownloadedFileWithDownloadModel:downloadModel]) return NO;
    return YES;
}

-(void)setValuesForDownloadModel:(FKNetworkingDownloadModel *)downloadModel withProgress:(double)progress{
    NSTimeInterval interval = -1 * [downloadModel.downloadDate timeIntervalSinceNow];
    downloadModel.progressModel.totalBytesWritten = downloadModel.downloadTask.countOfBytesReceived;
    downloadModel.progressModel.totalBytesExpectedToWrite = downloadModel.downloadTask.countOfBytesExpectedToReceive;
    downloadModel.progressModel.downloadProgress = progress;
    downloadModel.progressModel.downloadSpeed = (int64_t)((downloadModel.progressModel.totalBytesWritten - [self getResumeByteWithDownloadModel:downloadModel]) / interval);
    if (downloadModel.progressModel.downloadSpeed != 0) {
        int64_t remainingContentLength = downloadModel.progressModel.totalBytesExpectedToWrite  - downloadModel.progressModel.totalBytesWritten;    
        int currentLeftTime = (int)(remainingContentLength / downloadModel.progressModel.downloadSpeed);
        downloadModel.progressModel.downloadLeft = currentLeftTime;
    }
}

-(int64_t)getResumeByteWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    int64_t resumeBytes = 0;
    NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:downloadModel.plistFilePath];
    if (dict) {
        resumeBytes = [dict[@"NSURLSessionResumeBytesReceived"] longLongValue]; 
    }
    return resumeBytes;
}

-(NSString *)getTmpFileNameWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    NSString *fileName = nil;
    NSDictionary *dict = [NSDictionary dictionaryWithContentsOfFile:downloadModel.plistFilePath];
    if (dict) {
        fileName = dict[@"NSURLSessionResumeInfoTempFileName"]; 
    }
    return fileName;
}

-(void)createFolderAtPath:(NSString *)path{
    if ([self.fileManager fileExistsAtPath:path]) return;
    [self.fileManager createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];
}

-(void)deletePlistFileWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    if (downloadModel.downloadTask.countOfBytesReceived == downloadModel.downloadTask.countOfBytesExpectedToReceive) {
        [self.fileManager removeItemAtPath:downloadModel.plistFilePath error:nil];
        [self removeTotalBytesExpectedToWriteWhenDownloadFinishedWithDownloadModel:downloadModel];
    }
}

-(NSString *)managerPlistFilePath{
    return [self.downloadDirectory stringByAppendingPathComponent:@"ForKidManager.plist"];
}

-(nullable NSMutableDictionary <NSString *, NSString *> *)managerPlistDict{
    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile:[self managerPlistFilePath]];
    return dict;
}

-(void)saveTotalBytesExpectedToWriteWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    NSMutableDictionary <NSString *, NSString *> *dict = [self managerPlistDict];
    [dict setValue:[NSString stringWithFormat:@"%lld", downloadModel.downloadTask.countOfBytesExpectedToReceive] forKey:downloadModel.resourceURLString];
    [dict writeToFile:[self managerPlistFilePath] atomically:YES];
}

-(void)removeTotalBytesExpectedToWriteWhenDownloadFinishedWithDownloadModel:(FKNetworkingDownloadModel *)downloadModel{
    NSMutableDictionary <NSString *, NSString *> *dict = [self managerPlistDict];
    [dict removeObjectForKey:downloadModel.resourceURLString];
    [dict writeToFile:[self managerPlistFilePath] atomically:YES];
}

#pragma mark - share instance
+(FKNetworkingManager *)shareManager{
    static FKNetworkingManager *manager = nil;
    static dispatch_once_t sigletonOnceToken;
    dispatch_once(&sigletonOnceToken, ^{
        manager = [[self alloc] init];
    });
    return manager;
}

- (instancetype)init{
    self = [super init];
    if (self) {
        _AFManager = [[AFHTTPSessionManager alloc]init];
        _AFManager.requestSerializer.timeoutInterval = 5;
        _AFManager.requestSerializer.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;//NSURLRequestUseProtocolCachePolicy;
        NSSet *typeSet = [NSSet setWithObjects:@"application/json", @"text/plain", @"text/javascript", @"text/json", @"text/html", nil];
        _AFManager.responseSerializer.acceptableContentTypes = typeSet;
        _AFManager.securityPolicy.allowInvalidCertificates = YES;

        _maxDownloadCount = 1;
        _resumeTaskFIFO = YES;
        _batchDownload = NO;
        _fileManager = [NSFileManager defaultManager];
        _waitingModels = [[NSMutableArray alloc] initWithCapacity:1];
        _downloadingModels = [[NSMutableArray alloc] initWithCapacity:1];
        _downloadModelsDict = [[NSMutableDictionary alloc] initWithCapacity:1];

        _downloadDirectory = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject stringByAppendingPathComponent:FKNetworkingManagerFileName];
        [_fileManager createDirectoryAtPath:_downloadDirectory withIntermediateDirectories:YES attributes:nil error:nil];

        NSDictionary <NSString *, NSString *> *plistDict = [[NSDictionary alloc] init];
        NSString *managerPlistFilePath = [_downloadDirectory stringByAppendingPathComponent:@"ForKidManager.plist"];
        [plistDict writeToFile:managerPlistFilePath atomically:YES];
    }
    return self;
}

@end

转自：http://www.jianshu.com/p/f311f7057faa