前言
AFNetWorking是日常开发中用的最多的网络框架了，平时仅限于对AF的一些封装，并没有对它从源码了解过，趁着有空，了解一下它的实现。
架构了解一哈
NSURLSession（网络通信模块）
AFURLSessionManagerAFHTTPSessionManager
Serialization（网络通信信息序列化/反序列化模块）
-
<AFURLRequestSerialization>AFHTTPRequestSerializerAFJSONRequestSerializerAFPropertyListRequestSerializer
-
<AFURLResponseSerialization>AFHTTPResponseSerializerAFJSONResponseSerializerAFXMLParserResponseSerializer-
AFXMLDocumentResponseSerializer(macOS) AFPropertyListResponseSerializerAFImageResponseSerializerAFCompoundResponseSerializer
Additional Functionality（网络通信安全模块，网络状态监听模块）
AFSecurityPolicyAFNetworkReachabilityManager
AF的核心模块当然是AFURLSessionManager.AF3.x是基于NSURLSession封装的。其余的模块都是配合网络通信的。至于AFHTTPSessionManager，它其实是继承自AFURLSessionManager,为了更加方便的来做一些网络请求。
先写一个简单的网络请求
NSString *getUrl = @"https://httpbin.org/get";
AFHTTPSessionManager *manage = [AFHTTPSessionManager manager];
NSDictionary *dict = @{@"index":@"1",
@"page":@"2"
};
//这个请求没有具体内容返回，主要是测试request的post方式的参数处理
[manage POST:getUrl parameters:dict progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"%@", responseObject);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"%@", error);
}];
首先初始化了一个manager，点击进去查看源码
+ (instancetype)manager {
return [[[self class] alloc] initWithBaseURL:nil];
}
- (instancetype)init {
return [self initWithBaseURL:nil];
}
- (instancetype)initWithBaseURL:(NSURL *)url {
return [self initWithBaseURL:url sessionConfiguration:nil];
}
- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
return [self initWithBaseURL:nil sessionConfiguration:configuration];
}
- (instancetype)initWithBaseURL:(NSURL *)url
sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
self = [super initWithSessionConfiguration:configuration];
if (!self) {
return nil;
}
// Ensure terminal slash for baseURL path, so that NSURL +URLWithString:relativeToURL: works as expected
if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
url = [url URLByAppendingPathComponent:@""];
}
self.baseURL = url;
self.requestSerializer = [AFHTTPRequestSerializer serializer];
self.responseSerializer = [AFJSONResponseSerializer serializer];
return self;
}
- 初始化的方法在本类中始终调用了
- (instancetype)initWithBaseURL:(NSURL *)url sessionConfiguration:(NSURLSessionConfiguration *)configuration， - 该方法实际调用的是父类的
- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration
点击进入父类AFURLSessionManager中，查看初始化方法源码
- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
self = [super init];
if (!self) {
return nil;
}
if (!configuration) {
configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
}
self.sessionConfiguration = configuration;
self.operationQueue = [[NSOperationQueue alloc] init];
//设置最大并发数量为1
self.operationQueue.maxConcurrentOperationCount = 1;
//设置session的代理为
self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];
//设置相应解析器
self.responseSerializer = [AFJSONResponseSerializer serializer];
//设置安全策略
self.securityPolicy = [AFSecurityPolicy defaultPolicy];
#if !TARGET_OS_WATCH
self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
#endif
//这个字典里存放着每个task对应的AFURLSessionManagerTaskDelegate
self.mutableTaskDelegatesKeyedByTaskIdentifier = [[NSMutableDictionary alloc] init];
//设置AFURLSessionManagerTaskDelegate字典的锁，确保字典在多线程访问时的线程安全
self.lock = [[NSLock alloc] init];
self.lock.name = AFURLSessionManagerLockName;
[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;
}
- (void)getTasksWithCompletionHandler:(void (^)(NSArray<NSURLSessionDataTask *> *dataTasks, NSArray<NSURLSessionUploadTask *> *uploadTasks, NSArray<NSURLSessionDownloadTask *> *downloadTasks))completionHandler;该方法是用来一步获取当前未完成的task任务
- (void)addDelegateForUploadTask:(NSURLSessionUploadTask *)uploadTask progress:(void (^)(NSProgress *uploadProgress)) uploadProgressBlock completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
在类似的方法里都调用了- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate forTask:(NSURLSessionTask *)task，这里就涉及到self.mutableTaskDelegatesKeyedByTaskIdentifier字典，通过self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;来绑定task和对应的delegate。
初始化流程到这里就结束了，接下来看看网络请求：
- (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
{
//初始化一个task
NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"GET"
URLString:URLString
parameters:parameters
uploadProgress:nil
downloadProgress:downloadProgress
success:success
failure:failure];
//开始请求
[dataTask resume];
return dataTask;
}
初始化方法调用的是父类的方法来生成一个NSURLSessionDataTask对象，然后开始请求，接着看
- (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;
//将请求的url，参数转化成一个NSMutableURLRequest请求
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;
}
这个方法实际做了一下的事
- 通过URL和参数获取一个最终的
NSMutableURLRequest请求对象 - 调用另外的方法
dataTaskWithRequest来获取实际的需要的NSURLSessionDataTask对象，然后在完成的回调，传回成功失败的回调
先看看如何生成NSMutableURLRequest对象，到AFURLRequestSerialization中找到方法
- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
URLString:(NSString *)URLString
parameters:(id)parameters
error:(NSError *__autoreleasing *)error
{
NSParameterAssert(method);
NSParameterAssert(URLString);
NSURL *url = [NSURL URLWithString:URLString];
NSParameterAssert(url);
NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
mutableRequest.HTTPMethod = method;
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
//如果自己观察的属性有变化，重新赋值（包含缓存策略，超时时间等等）
if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
[mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
}
}
//将参数进行编码，添加到request中
mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];
return mutableRequest;
}
这个方法做了三件事
1.设置请求方法（post，get...）
2.向request中添加参数，self.mutableObservedChangedKeyPaths是本类的一个属性，在- (instancetype)init中初始化。
self.mutableObservedChangedKeyPaths = [NSMutableSet set];
//给这自己些方法添加观察者为自己，就是request的各种属性，set方法
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
[self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:AFHTTPRequestSerializerObserverContext];
}
}
对当前类的和NSURLRequest相关的属性进行监听
KVO触发方法
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(__unused id)object
change:(NSDictionary *)change
context:(void *)context
{
if (context == AFHTTPRequestSerializerObserverContext) {
if ([change[NSKeyValueChangeNewKey] isEqual:[NSNull null]]) {
[self.mutableObservedChangedKeyPaths removeObject:keyPath];
} else {
[self.mutableObservedChangedKeyPaths addObject:keyPath];
}
}
}
如果这些属性的set方法被调用了，该属性就会被添加进self.mutableObservedChangedKeyPaths，否则就会移除该属性
回到requestWithMethod方法，其中有一个方法AFHTTPRequestSerializerObservedKeyPaths()返回的是一个数组
static NSArray * AFHTTPRequestSerializerObservedKeyPaths() {
static NSArray *_AFHTTPRequestSerializerObservedKeyPaths = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_AFHTTPRequestSerializerObservedKeyPaths = @[NSStringFromSelector(@selector(allowsCellularAccess)), NSStringFromSelector(@selector(cachePolicy)), NSStringFromSelector(@selector(HTTPShouldHandleCookies)), NSStringFromSelector(@selector(HTTPShouldUsePipelining)), NSStringFromSelector(@selector(networkServiceType)), NSStringFromSelector(@selector(timeoutInterval))];
});
return _AFHTTPRequestSerializerObservedKeyPaths;
}
数组中的东西都很熟悉，都是NSURLRequest的一些属性。
3.把需要的参数编码，添加到request中。
- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
withParameters:(id)parameters
error:(NSError *__autoreleasing *)error
{
NSParameterAssert(request);
NSMutableURLRequest *mutableRequest = [request mutableCopy];
//将自己的请求头设置给request
[self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
if (![request valueForHTTPHeaderField:field]) {
[mutableRequest setValue:value forHTTPHeaderField:field];
}
}];
//传入的参数做处理,转化成NSString类型
NSString *query = nil;
if (parameters) {
if (self.queryStringSerialization) { //自定义的解析方式
NSError *serializationError;
query = self.queryStringSerialization(request, parameters, &serializationError);
if (serializationError) {
if (error) {
*error = serializationError;
}
return nil;
}
} else { //AF默认的解析模式
switch (self.queryStringSerializationStyle) {
case AFHTTPRequestQueryStringDefaultStyle:
query = AFQueryStringFromParameters(parameters);
break;
}
}
}
/**
HTTP methods for which serialized requests will encode parameters as a query string. `GET`, `HEAD`, and `DELETE` by default.如果请求方法是这三种，直接拼接在URL后，否则后拼接到HTTP Body中
*/
if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
if (query && query.length > 0) {
mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
}
} else {
// #2864: an empty string is a valid x-www-form-urlencoded payload
if (!query) {
query = @"";
}
if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
[mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
}
//设置请求体
[mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
}
return mutableRequest;
}
该方法做了一下几件事
- 从
self.HTTPRequestHeaders取值赋值给request - 将请求的参数转化成
NSString类型，AF默认的装换方法如下：
NSString * AFQueryStringFromParameters(NSDictionary *parameters) {
NSMutableArray *mutablePairs = [NSMutableArray array];
for (AFQueryStringPair *pair in AFQueryStringPairsFromDictionary(parameters)) {
[mutablePairs addObject:[pair URLEncodedStringValue]];
}
return [mutablePairs componentsJoinedByString:@"&"];
}
NSArray * AFQueryStringPairsFromDictionary(NSDictionary *dictionary) {
return AFQueryStringPairsFromKeyAndValue(nil, dictionary);
}
NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value) {
NSMutableArray *mutableQueryStringComponents = [NSMutableArray array];
//通过需要排序的对象的description方法来升序排序，使用compare方法排序
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"description" ascending:YES selector:@selector(compare:)];
//判断value的类型，NSDictionary，NSArray，NSSet，递归调用自身，直到解析的内容不是上述三个类
if ([value isKindOfClass:[NSDictionary class]]) {
NSDictionary *dictionary = value;
// Sort dictionary keys to ensure consistent ordering in query string, which is important when deserializing potentially ambiguous sequences, such as an array of dictionaries
for (id nestedKey in [dictionary.allKeys sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
id nestedValue = dictionary[nestedKey];
if (nestedValue) {
[mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue((key ? [NSString stringWithFormat:@"%@[%@]", key, nestedKey] : nestedKey), nestedValue)];
}
}
} else if ([value isKindOfClass:[NSArray class]]) {
NSArray *array = value;
for (id nestedValue in array) {
[mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue([NSString stringWithFormat:@"%@[]", key], nestedValue)];
}
} else if ([value isKindOfClass:[NSSet class]]) {
NSSet *set = value;
for (id obj in [set sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
[mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue(key, obj)];
}
} else {
[mutableQueryStringComponents addObject:[[AFQueryStringPair alloc] initWithField:key value:value]];
}
return mutableQueryStringComponents;
}
NSSortDescriptor这个排序类，可以看这篇文章，讲的很仔细了。以上流程只要选择POST请求，并带上参数，打个断点很容易看懂AF具体干了什么。最后将我们的传入的参数转变成字符串了。到此，一个request对象就算完成了。
