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iOS开发·网络下载总结(NSURLConnection,NSURLSession,AFNetw

2018-07-10 18:10 出处:清屏网 人气: 评论(0

0. 前言

iOS的开发中的网络下载方式包括NSData(最原始,实际开发基本不会用),NSURLConnection(古老又过气的苹果原生网络框架),NSURLSession(现在流行的苹果网络框架),AFNetworking,SDWebImage以及基于AFNetworking的二次封装框架例如XMNetworking,HYBNetworking等等。

NSURLConnection作为过气的框架,作为对比了解一下还是有必要的。NSURLSession作为众多网络相关的第三方框架基于的苹果原生框架,更是有必要学习总结一下。作为第三方框架,AFNetworking,SDWebImage等等其实它们的老版本是基于NSURLConnection封装而成的,后来才改成的基于NSURLSession。这些第三方框架相比原生框架封装了缓存的逻辑,比如内存缓存,磁盘缓存,操作缓存等等。

0.1 最原始的网络下载 -- NSData+NSURL方式

关键步骤

NSString-->NSURL-->NSData-->UIImage

关键API

URLWithString
dataWithContentsOfURL:url
imageWithData:data

下载示例

/**
 * 点击按钮 -- 使用NSData下载图片文件,并显示再imageView上
 */
- (IBAction)downloadBtnClick:(UIButton *)sender {

    // 在子线程中发送下载文件请求
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // 创建下载路径
        NSURL *url = [NSURL URLWithString:@"https://upload-images.jianshu.io/upload_images/1877784-b4777f945878a0b9.jpg"];

        // NSData的dataWithContentsOfURL:方法下载
        NSData *data = [NSData dataWithContentsOfURL:url];

        // 回到主线程,刷新UI
        dispatch_async(dispatch_get_main_queue(), ^{

            self.imageView.image = [UIImage imageWithData:data];
        });
    });
}

1. 过气的苹果原生网络框架 -- NSURLConnection

① 下载完的事件采用block形式的API

//handler   A block which receives the results of the resource load.
+ (void)sendAsynchronousRequest:(NSURLRequest*) request
                          queue:(NSOperationQueue*) queue
              completionHandler:(void (^)(NSURLResponse* _Nullable response, NSData* _Nullable data, NSError* _Nullable connectionError)) handler API_DEPRECATED("Use [NSURLSession dataTaskWithRequest:completionHandler:] (see NSURLSession.h", macos(10.7,10.11), ios(5.0,9.0), tvos(9.0,9.0)) __WATCHOS_PROHIBITED;

② 下载完的事件采用delegate形式的API

/* Designated initializer */
- (nullable instancetype)initWithRequest:(NSURLRequest *)request delegate:(nullable id)delegate startImmediately:(BOOL)startImmediately API_DEPRECATED("Use NSURLSession (see NSURLSession.h)", macos(10.5,10.11), ios(2.0,9.0), tvos(9.0,9.0)) __WATCHOS_PROHIBITED;

- (nullable instancetype)initWithRequest:(NSURLRequest *)request delegate:(nullable id)delegate API_DEPRECATED("Use NSURLSession (see NSURLSession.h)", macos(10.3,10.11), ios(2.0,9.0), tvos(9.0,9.0)) __WATCHOS_PROHIBITED;
+ (nullable NSURLConnection*)connectionWithRequest:(NSURLRequest *)request delegate:(nullable id)delegate API_DEPRECATED("Use NSURLSession (see NSURLSession.h)", macos(10.3,10.11), ios(2.0,9.0), tvos(9.0,9.0)) __WATCHOS_PROHIBITED;

调用示例 -- 采用block的API ①

/**
 * 点击按钮 -- 使用NSURLConnection下载图片文件,并显示再imageView上
 */
- (IBAction)downloadBtnClicked:(UIButton *)sender {
    // 创建下载路径
    NSURL *url = [NSURL URLWithString:@"https://upload-images.jianshu.io/upload_images/1877784-b4777f945878a0b9.jpg"];

    // NSURLConnection发送异步Get请求,该方法iOS9.0之后就废除了,推荐NSURLSession
    [NSURLConnection sendAsynchronousRequest:[NSURLRequest requestWithURL:url] queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {

        self.imageView.image = [UIImage imageWithData:data];

        // 可以在这里把下载的文件保存
    }];

}

调用示例 -- 采用delegate的API ②

- (IBAction)downloadBtnClicked:(UIButton *)sender {
    // 创建下载路径
    NSURL *url = [NSURL URLWithString:@"http://dldir1.qq.com/qqfile/QQforMac/QQ_V5.4.0.dmg"];
    // NSURLConnection发送异步Get请求,并实现相应的代理方法,该方法iOS9.0之后废除了。
    [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:url] delegate:self];
}

代理实现方法示例

#pragma mark 
  
     实现方法

/**
 * 接收到响应的时候:创建一个空的沙盒文件
 */
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // 获得下载文件的总长度
    self.fileLength = response.expectedContentLength;

    // 沙盒文件路径
    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"QQ_V5.4.0.dmg"];

    NSLog(@"File downloaded to: %@",path);

    // 创建一个空的文件到沙盒中
    [[NSFileManager defaultManager] createFileAtPath:path contents:nil attributes:nil];

    // 创建文件句柄
    self.fileHandle = [NSFileHandle fileHandleForWritingAtPath:path];
}

/**
 * 接收到具体数据:把数据写入沙盒文件中
 */
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // 指定数据的写入位置 -- 文件内容的最后面
    [self.fileHandle seekToEndOfFile];

    // 向沙盒写入数据
    [self.fileHandle writeData:data];

    // 拼接文件总长度
    self.currentLength += data.length;

    // 下载进度
    self.progressView.progress =  1.0 * self.currentLength / self.fileLength;
    self.progressLabel.text = [NSString stringWithFormat:@"当前下载进度:%.2f%%",100.0 * self.currentLength / self.fileLength];
}

/**
 *  下载完文件之后调用:关闭文件、清空长度
 */
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // 关闭fileHandle
    [self.fileHandle closeFile];
    self.fileHandle = nil;

    // 清空长度
    self.currentLength = 0;
    self.fileLength = 0;
}

2. 现在的苹果原生网络框架 -- NSURLSession

在iOS9.0之后,以前使用的NSURLConnection过期,苹果推荐使用NSURLSession来替换NSURLConnection完成网路请求相关操作。NSURLSession的使用非常简单,先根据会话对象创建一个请求Task,然后执行该Task即可。NSURLSessionTask本身是一个抽象类,在使用的时候,通常是根据具体的需求使用它的几个子类。关系如下:

2.1 GET请求(NSURLRequest默认设置)

使用 NSURLSession 发送GET请求的方法和 NSURLConnection 类似,整个过程如下:

1)确定请求路径(一般由公司的后台开发人员以接口文档的方式提供),GET请求参数直接跟在URL后面
2)创建请求对象(默认包含了请求头和请求方法【GET】),此步骤可以省略
3)创建会话对象(NSURLSession)
4)根据会话对象创建请求任务(NSURLSessionDataTask)
5)执行Task
6)当得到服务器返回的响应后,解析数据(XML|JSON|HTTP)

① 下载完的事件采用block形式

get请求示例1

关键API

sharedSession
requestWithURL:
dataTaskWithRequest:
-(void)getWithBlock1
{
    //对请求路径的说明
    //http://120.25.226.186:32812/login?username=520it&pwd=520&type=JSON
    //协议头+主机地址+接口名称+?+参数1&参数2&参数3
    //协议头(http://)+主机地址(120.25.226.186:32812)+接口名称(login)+?+参数1(username=520it)&参数2(pwd=520)&参数3(type=JSON)
    //GET请求,直接把请求参数跟在URL的后面以?隔开,多个参数之间以&符号拼接

    //1.确定请求路径
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/login?username=520it&pwd=520it&type=JSON"];

    //2.创建请求对象
    //请求对象内部默认已经包含了请求头和请求方法(GET)
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    //3.获得会话对象
    NSURLSession *session = [NSURLSession sharedSession];

    //4.根据会话对象创建一个Task(发送请求)
    /*
     第一个参数:请求对象
     第二个参数:completionHandler回调(请求完成【成功|失败】的回调)
               data:响应体信息(期望的数据)
               response:响应头信息,主要是对服务器端的描述
               error:错误信息,如果请求失败,则error有值
     */
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

        if (error == nil) {
            //6.解析服务器返回的数据
            //说明:(此处返回的数据是JSON格式的,因此使用NSJSONSerialization进行反序列化处理)
            NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

            NSLog(@"%@",dict);
        }
    }];

    //5.执行任务
    [dataTask resume];
}

get请求示例2

关键API

sharedSession
dataTaskWithURL:
-(void)getWithBlock2
{
    //1.确定请求路径
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/login?username=520it&pwd=520it&type=JSON"];

    //2.获得会话对象
    NSURLSession *session = [NSURLSession sharedSession];

    //3.根据会话对象创建一个Task(发送请求)
    /*
     第一个参数:请求路径
     第二个参数:completionHandler回调(请求完成【成功|失败】的回调)
               data:响应体信息(期望的数据)
               response:响应头信息,主要是对服务器端的描述
               error:错误信息,如果请求失败,则error有值
     注意:
        1)该方法内部会自动将请求路径包装成一个请求对象,该请求对象默认包含了请求头信息和请求方法(GET)
        2)如果要发送的是POST请求,则不能使用该方法
     */
    NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

        //5.解析数据
        NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
        NSLog(@"%@",dict);

    }];

    //4.执行任务
    [dataTask resume];
}

② 下载完的事件采用delegate形式

关键API

requestWithURL:
sessionWithConfiguration
dataTaskWithRequest:request

get请求发起示例

-(void) getWithDelegate1
{
    //1.确定请求路径
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/login?username=520it&pwd=520it&type=JSON"];

    //2.创建请求对象
    //请求对象内部默认已经包含了请求头和请求方法(GET)
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    //3.获得会话对象,并设置代理
    /*
     第一个参数:会话对象的配置信息defaultSessionConfiguration 表示默认配置
     第二个参数:谁成为代理,此处为控制器本身即self
     第三个参数:队列,该队列决定代理方法在哪个线程中调用,可以传主队列|非主队列
     [NSOperationQueue mainQueue]   主队列:   代理方法在主线程中调用
     [[NSOperationQueue alloc]init] 非主队列: 代理方法在子线程中调用
     */
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];

    //4.根据会话对象创建一个Task(发送请求)
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request];

    //5.执行任务
    [dataTask resume];
}

代理关键API

//1.接收到服务器响应的时候调用该方法
-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{

//2.接收到服务器返回数据的时候会调用该方法,如果数据较大那么该方法可能会调用多次
-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{

//3.当请求完成(成功|失败)的时候会调用该方法,如果请求失败,则error有值
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{

代理实现示例

#pragma mark NSURLSessionDataDelegate
//1.接收到服务器响应的时候调用该方法
-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
    //在该方法中可以得到响应头信息,即response
    NSLog(@"didReceiveResponse--%@",[NSThread currentThread]);

    //注意:需要使用completionHandler回调告诉系统应该如何处理服务器返回的数据
    //默认是取消的
    /*
     NSURLSessionResponseCancel = 0,        默认的处理方式,取消
     NSURLSessionResponseAllow = 1,         接收服务器返回的数据
     NSURLSessionResponseBecomeDownload = 2,变成一个下载请求
     NSURLSessionResponseBecomeStream        变成一个流
     */

    completionHandler(NSURLSessionResponseAllow);
}

//2.接收到服务器返回数据的时候会调用该方法,如果数据较大那么该方法可能会调用多次
-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
    NSLog(@"didReceiveData--%@",[NSThread currentThread]);

    //拼接服务器返回的数据
    [self.responseData appendData:data];
}

//3.当请求完成(成功|失败)的时候会调用该方法,如果请求失败,则error有值
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    NSLog(@"didCompleteWithError--%@",[NSThread currentThread]);

    if(error == nil)
    {
        //解析数据,JSON解析请参考http://www.cnblogs.com/wendingding/p/3815303.html
        NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:self.responseData options:kNilOptions error:nil];
        NSLog(@"%@",dict);
    }
}

如下图所示,get请求内部封装了开始操作(其实是继续),不用再像NSURLSession一样外面resume了。

2.2 POST请求(需另外单独设置request.HTTPMethod属性)

post请求示例

关键API

sharedSession
requestWithURL:
request.HTTPMethod = @"POST";
dataTaskWithRequest:request completionHandler:
-(void)postWithBlock
{
    //对请求路径的说明
    //http://120.25.226.186:32812/login
    //协议头+主机地址+接口名称
    //协议头(http://)+主机地址(120.25.226.186:32812)+接口名称(login)
    //POST请求需要修改请求方法为POST,并把参数转换为二进制数据设置为请求体

    //1.创建会话对象
    NSURLSession *session = [NSURLSession sharedSession];

    //2.根据会话对象创建task
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/login"];

    //3.创建可变的请求对象
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

    //4.修改请求方法为POST
    request.HTTPMethod = @"POST";

    //5.设置请求体
    request.HTTPBody = [@"username=520it&pwd=520it&type=JSON" dataUsingEncoding:NSUTF8StringEncoding];

    //6.根据会话对象创建一个Task(发送请求)
    /*
     第一个参数:请求对象
     第二个参数:completionHandler回调(请求完成【成功|失败】的回调)
                data:响应体信息(期望的数据)
                response:响应头信息,主要是对服务器端的描述
                error:错误信息,如果请求失败,则error有值
     */
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

        //8.解析数据
        NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
        NSLog(@"%@",dict);

    }];

    //7.执行任务
    [dataTask resume];
}

3. HTTPS与HTTP的不同点

前面涉及到的GET和POST都属于HTTP请求,现在苹果的APP都推荐支持HTTPS,这就需要先配置一下证书,然后在NSURLSession(或者NSURLConnection但现在新的项目基本不用了)的代理方法里面进行一些特别的操作。如果是AFNetWorking,也需要对AFHTTPRequestOperationManager对象进行一些特别的操作。

关于证书的配置,及需要的特别的操作,推荐阅读:

/uploads/allimg/180710/1Q0501940-1.jpg

/uploads/allimg/180710/1Q0505S5-2.jpg

/uploads/allimg/180710/1Q0502Z1-3.jpg

4. AF封装了GET和POST操作的 -- AFHTTPSessionManager

AFNetworking2.0和3.0区别很大,也是因为苹果废弃了NSURLConnection,而改用了NSURLSession,AFNetworking3.0实际上只是对NSURLSession所做的操作进行了高度封装,提供更加简洁的API供编码调用。

查看AFHTTPSessionManager.h文件,可知AFHTTPSessionManager是AFURLSessionManager的子类:

@interface AFHTTPSessionManager : AFURLSessionManager <NSSecureCoding, NSCopying>

请求示例 -- 下载一个PDF文件

- (void)DownloadPdfAndSave{
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    manager.responseSerializer = [AFHTTPResponseSerializer serializer];
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"application/pdf"];
    __weak __typeof__(self) weakSelf = self;
    //临时配置,需要自己根据接口地址改动!!!!!!!!!!!!!!!!!!!!
    self.urlStr = @"http://10.20.201.78/test3.pdf";
    [manager GET:_urlStr parameters:nil progress:^(NSProgress * _Nonnull downloadProgress) {
    } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        __strong __typeof__(weakSelf) strongSelf = weakSelf;
        strongSelf.isWriten = [responseObject writeToFile:[self pathOfPdf] atomically:YES];
        [strongSelf openPdfByAddingSubView];
        //[strongSelf.previewController reloadData];
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        NSLog(@"%@",error.userInfo);
    }];
}

get请求调用栈分析

AFHTTPSessionManager.m
- (NSURLSessionDataTask *)GET:(NSString *)URLString
                   parameters:(id)parameters
                      success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                      failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{

    return [self GET:URLString parameters:parameters progress:nil success:success failure:failure];
}
- (NSURLSessionDataTask *)GET:(NSString *)URLString
                   parameters:(id)parameters
                     progress:(void (^)(NSProgress * _Nonnull))downloadProgress
                      success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
                      failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{

    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"GET"
                                                        URLString:URLString
                                                       parameters:parameters
                                                   uploadProgress:nil
                                                 downloadProgress:downloadProgress
                                                          success:success
                                                          failure:failure];

    [dataTask resume];

    return dataTask;
}
- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
                                       URLString:(NSString *)URLString
                                      parameters:(id)parameters
                                  uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
                                downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
                                         success:(void (^)(NSURLSessionDataTask *, id))success
                                         failure:(void (^)(NSURLSessionDataTask *, NSError *))failure
{
    NSError *serializationError = nil;
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }

        return nil;
    }

    __block NSURLSessionDataTask *dataTask = nil;
    dataTask = [self dataTaskWithRequest:request
                          uploadProgress:uploadProgress
                        downloadProgress:downloadProgress
                       completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
        if (error) {
            if (failure) {
                failure(dataTask, error);
            }
        } else {
            if (success) {
                success(dataTask, responseObject);
            }
        }
    }];

    return dataTask;
}

AFURLSessionManager.m

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                               uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
                             downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                            completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler {

    __block NSURLSessionDataTask *dataTask = nil;
    url_session_manager_create_task_safely(^{
        dataTask = [self.session dataTaskWithRequest:request];
    });

    [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];

    return dataTask;
}

5. AF的GET和POST请求实现第二层 -- AFURLSessionManager

5.1 downloadTaskWithRequest: progress: destination: completionandler:

AFURLSessionManager.m

调用示例

DownloadVC.m

- (IBAction)downloadBtnClicked:(UIButton *)sender {

    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    // 1. 创建会话管理者
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

    // 2. 创建下载路径和请求对象
    NSURL *URL = [NSURL URLWithString:@"http://dldir1.qq.com/qqfile/QQforMac/QQ_V5.4.0.dmg"];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];

    // 3.创建下载任务
    /**
     * 第一个参数 - request:请求对象
     * 第二个参数 - progress:下载进度block
     *      其中: downloadProgress.completedUnitCount:已经完成的大小
     *            downloadProgress.totalUnitCount:文件的总大小
     * 第三个参数 - destination:自动完成文件剪切操作
     *      其中: 返回值:该文件应该被剪切到哪里
     *            targetPath:临时路径 tmp NSURL
     *            response:响应头
     * 第四个参数 - completionHandler:下载完成回调
     *      其中: filePath:真实路径 == 第三个参数的返回值
     *            error:错误信息
     */
    NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:^(NSProgress *downloadProgress) {

        __weak typeof(self) weakSelf = self;
        // 获取主线程,不然无法正确显示进度。
        NSOperationQueue* mainQueue = [NSOperationQueue mainQueue];
        [mainQueue addOperationWithBlock:^{
            // 下载进度
            weakSelf.progressView.progress = 1.0 * downloadProgress.completedUnitCount / downloadProgress.totalUnitCount;
            weakSelf.progressLabel.text = [NSString stringWithFormat:@"当前下载进度:%.2f%%",100.0 * downloadProgress.completedUnitCount / downloadProgress.totalUnitCount];
        }];


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

        NSURL *path = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
        return [path URLByAppendingPathComponent:@"QQ_V5.4.0.dmg"];

    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {

        NSLog(@"File downloaded to: %@", filePath);
    }];

    // 4. 开启下载任务
    [downloadTask resume];
}

内部封装分析

AFURLSessionManager.m

- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
                                             progress:(void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                                          destination:(NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
                                    completionHandler:(void (^)(NSURLResponse *response, NSURL *filePath, NSError *error))completionHandler
{
    __block NSURLSessionDownloadTask *downloadTask = nil;
    url_session_manager_create_task_safely(^{
        downloadTask = [self.session downloadTaskWithRequest:request];
    });

    [self addDelegateForDownloadTask:downloadTask progress:downloadProgressBlock destination:destination completionHandler:completionHandler];

    return downloadTask;
}

其中self.session是AFURLSessionManager.h中的属性

@property (readonly, nonatomic, strong) NSURLSession *session;

它后面调用的API声明在NSFoundation的NSURLSession.h的头文件中

/* Creates a data task with the given request.  The request may have a body stream. */
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;

添加代理的封装

AFURLSessionManager.m

- (void)addDelegateForDataTask:(NSURLSessionDataTask *)dataTask
                uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
              downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
             completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
    AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] init];
    delegate.manager = self;
    delegate.completionHandler = completionHandler;

    dataTask.taskDescription = self.taskDescriptionForSessionTasks;
    [self setDelegate:delegate forTask:dataTask];

    delegate.uploadProgressBlock = uploadProgressBlock;
    delegate.downloadProgressBlock = downloadProgressBlock;
}

其中

- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
            forTask:(NSURLSessionTask *)task
{
    NSParameterAssert(task);
    NSParameterAssert(delegate);

    [self.lock lock];
    self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
    [delegate setupProgressForTask:task];
    [self addNotificationObserverForTask:task];
    [self.lock unlock];
}

其中,self.mutableTaskDelegatesKeyedByTaskIdentifier是个字典

@property (readwrite, nonatomic, strong) NSMutableDictionary *mutableTaskDelegatesKeyedByTaskIdentifier;

被调用的地方在:

- (AFURLSessionManagerTaskDelegate *)delegateForTask:(NSURLSessionTask *)task {
    NSParameterAssert(task);

    AFURLSessionManagerTaskDelegate *delegate = nil;
    [self.lock lock];
    delegate = self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)];
    [self.lock unlock];

    return delegate;
}

进而被调用的地方在:

- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:downloadTask];
    if (self.downloadTaskDidFinishDownloading) {
        NSURL *fileURL = self.downloadTaskDidFinishDownloading(session, downloadTask, location);
        if (fileURL) {
            delegate.downloadFileURL = fileURL;
            NSError *error = nil;
            [[NSFileManager defaultManager] moveItemAtURL:location toURL:fileURL error:&error];
            if (error) {
                [[NSNotificationCenter defaultCenter] postNotificationName:AFURLSessionDownloadTaskDidFailToMoveFileNotification object:downloadTask userInfo:error.userInfo];
            }

            return;
        }
    }

    if (delegate) {
        [delegate URLSession:session downloadTask:downloadTask didFinishDownloadingToURL:location];
    }
}

5.2 dataTaskWithRequest: completionHandler:

说明:这个NSURLSession的API容易跟AFURLSessionManager的API混淆,参数都是一个request和一个handler block。

NSURLSession的API是这样的:

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler
{

而AFURLSessionManager的API是这样的,可以对比学习下:

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{

调用示例 -- dataTaskWithRequest:

DownloadVC.m

 // 创建下载URL
        NSURL *url = [NSURL URLWithString:@"http://dldir1.qq.com/qqfile/QQforMac/QQ_V5.4.0.dmg"];

        // 2.创建request请求
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

        // 设置HTTP请求头中的Range
        NSString *range = [NSString stringWithFormat:@"bytes=%zd-", self.currentLength];
        [request setValue:range forHTTPHeaderField:@"Range"];

        __weak typeof(self) weakSelf = self;
        _downloadTask = [self.manager dataTaskWithRequest:request completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
            NSLog(@"dataTaskWithRequest");

            // 清空长度
            weakSelf.currentLength = 0;
            weakSelf.fileLength = 0;

            // 关闭fileHandle
            [weakSelf.fileHandle closeFile];
            weakSelf.fileHandle = nil;

        }];

其中self.manager是懒加载得到的AFURLSessionManager

/**
 * manager的懒加载
 */
- (AFURLSessionManager *)manager {
    if (!_manager) {
        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
        // 1. 创建会话管理者
        _manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];
    }
    return _manager;
}

内部封装分析

AFURLSessionManager.m
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                            completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
    return [self dataTaskWithRequest:request uploadProgress:nil downloadProgress:nil completionHandler:completionHandler];
}
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                               uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
                             downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                            completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler {

    __block NSURLSessionDataTask *dataTask = nil;
    url_session_manager_create_task_safely(^{
        dataTask = [self.session dataTaskWithRequest:request];
    });

    [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];

    return dataTask;
}

6. 调用栈分析

初始化AFHTTPSessionManager的内部实现调用栈

[AFHTTPSessionManager initWithBaseURL:]
        [AFHTTPSessionManager initWithBaseURL:sessionConfiguration:]
                [AFURLSessionManager initWithSessionConfiguration:] // 调用了父类AFURLSessionManager的初始化方法
                        [NSURLSession sessionWithConfiguration:delegate:delegateQueue:] // 调用了原生类NSURLSession的初始化方法
                        [AFJSONResponseSerializer serializer]
                        [AFSecurityPolicy defaultPolicy]
                        [AFNetworkReachabilityManager sharedManager]
                [AFHTTPRequestSerializer serializer]
                [AFJSONResponseSerializer serializer]

AFHTTPSessionManager发送请求的内部实现调用栈

[AFHTTPSessionManager GET:parameters:process:success:failure:]
        [AFHTTPSessionManager dataTaskWithHTTPMethod:parameters:uploadProgress:downloadProgress:success:failure:] // 【注解1】
                [AFHTTPRequestSerializer requestWithMethod:URLString:parameters:error:] // 获得NSMutableURLRequest
                [AFURLSessionManager dataTaskWithRequest:uploadProgress:downloadProgress:completionHandler:] // 【注解2】
                        [NSURLSession dataTaskWithRequest:] // 【注解3】
                        [AFURLSessionManager addDelegateForDataTask:uploadProgress:downloadProgress:completionHandler:] // 添加代理
                                [AFURLSessionManagerTaskDelegate init]
                                [AFURLSessionManager setDelegate:forTask:]
        [NSURLSessionDataTask resume]

其中,【注解1】、【注解2】、【注解3】这三个方法得到的是同一个对象,即【注解3】中系统原生的NSURLSessionDataTask对象。所以,AF请求操作内部实现也是和原生NSURLSession操作一样,创建task,调用resume发送请求。

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