源码阅读-AFNetworking之AFURLSessionManager (一)

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AFURLSessionManager 解析

AFNetworking 3.0 提供了 AFURLSessionManager 来处理 HTTP 请求, 使用方式如下:

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NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];
NSURL *URL = [NSURL URLWithString:@"http://example.com/upload"];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];
NSURLSessionDataTask *dataTask = [manager dataTaskWithRequest:request completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
    if (error) {
        NSLog(@"Error: %@", error);
    } else {
        NSLog(@"%@ %@", response, responseObject);
    }
}];
[dataTask resume];

不难看出, 3.0完全是基于 NSURLSession 来实现的, 下面我们就来看看源码中的实现细节

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- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
    self = [super init];
    if (!self) {
        return nil;
    }
    if (!configuration) {
        configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    }
    self.sessionConfiguration = configuration;
    //创建一个并行的队列, 但是 maxConcurrentOperationCount 设为 1, 相当于一个串行队列
    self.operationQueue = [[NSOperationQueue alloc] init];
    self.operationQueue.maxConcurrentOperationCount = 1;
    //初始化session, 传入 self.operationQueue
    self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];
    //设置 response 解析方式, 当成 JSON 来解析, 如果我们需要改变解析形式, 只需要在初始化之后修改 responseSerializer
    self.responseSerializer = [AFJSONResponseSerializer serializer];
    self.securityPolicy = [AFSecurityPolicy defaultPolicy];
#if !TARGET_OS_WATCH
    self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
#endif
    //一个用来存放task 所对应的 delegate 的 NSMutableDictionary, key 为TaskIdentifier, 其实就是内存指针地址
    self.mutableTaskDelegatesKeyedByTaskIdentifier = [[NSMutableDictionary alloc] init];
    //操作 mutableTaskDelegatesKeyedByTaskIdentifier 的时候使用的锁
    self.lock = [[NSLock alloc] init];
    self.lock.name = AFURLSessionManagerLockName;
    //清空 session 中 task 的所有 handler
    [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
        for (NSURLSessionDataTask *task in dataTasks) {
            [self addDelegateForDataTask:task uploadProgress:nil downloadProgress:nil completionHandler:nil];
        }
        for (NSURLSessionUploadTask *uploadTask in uploadTasks) {
            [self addDelegateForUploadTask:uploadTask progress:nil completionHandler:nil];
        }
        for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
            [self addDelegateForDownloadTask:downloadTask progress:nil destination:nil completionHandler:nil];
        }
    }];
    return self;
}

小技巧

NSFoundationVersionNumber 比较版本号

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#ifndef NSFoundationVersionNumber_iOS_8_0
#define NSFoundationVersionNumber_With_Fixed_5871104061079552_bug 1140.11
#else
#define NSFoundationVersionNumber_With_Fixed_5871104061079552_bug NSFoundationVersionNumber_iOS_8_0
#endif
    if (NSFoundationVersionNumber < NSFoundationVersionNumber_With_Fixed_5871104061079552_bug) {
        // Fix of bug
        // Open Radar:http://openradar.appspot.com/radar?id=5871104061079552 (status: Fixed in iOS8)
        // Issue about:https://github.com/AFNetworking/AFNetworking/issues/2093
        dispatch_sync(url_session_manager_creation_queue(), block);
    }

直接使用自带的NSFoundationVersionNumber来进行版本号的比较NSFoundationVersionNumber就是当前版本, NSFoundationVersionNumber_iOS_8_0就是 iOS8.0

NSStringFromSelector(@selector()) 来写keypath

使用NSStringFromSelector(@selector(countOfBytesReceived))来写keypath, 这样更直观。

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[task addObserver:self
       forKeyPath:NSStringFromSelector(@selector(countOfBytesReceived))
          options:NSKeyValueObservingOptionNew
          context:NULL];

用 dispatch_semaphore_t 把异步任务变成同步

通过dispatch_semaphore_t使getTasksWithCompletionHandler这个异步任务变成同步, 直到获得 tasks 才返回。NSStringFromSelector(_cmd)直接使用当前调用的函数为selector。

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- (NSArray *)tasksForKeyPath:(NSString *)keyPath {
    __block NSArray *tasks = nil;
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
        if ([keyPath isEqualToString:NSStringFromSelector(@selector(dataTasks))]) {
            tasks = dataTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(uploadTasks))]) {
            tasks = uploadTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(downloadTasks))]) {
            tasks = downloadTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(tasks))]) {
            tasks = [@[dataTasks, uploadTasks, downloadTasks] valueForKeyPath:@"@unionOfArrays.self"];
        }
        dispatch_semaphore_signal(semaphore);
    }];
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    return tasks;
}
- (NSArray *)tasks {
    return [self tasksForKeyPath:NSStringFromSelector(_cmd)];
}
- (NSArray *)dataTasks {
    return [self tasksForKeyPath:NSStringFromSelector(_cmd)];
}
- (NSArray *)uploadTasks {
    return [self tasksForKeyPath:NSStringFromSelector(_cmd)];
}
- (NSArray *)downloadTasks {
    return [self tasksForKeyPath:NSStringFromSelector(_cmd)];
}