版本记录
| 版本号 | 时间 |
|---|---|
| V1.0 | 2018.02.28 |
前言
我们做APP发起网络请求，都离不开一个非常有用的框架AFNetworking，可以说这个框架的知名度已经超过了苹果的底层网络请求部分，很多人可能不知道苹果底层是如何发起网络请求的，但是一定知道
AFNetworking，接下来几篇我们就一起详细的解析一下这个框架。感兴趣的可以看上面写的几篇。
1. AFNetworking源码探究（一） —— 基本介绍
2. AFNetworking源码探究（二） —— GET请求实现之NSURLSessionDataTask实例化（一）
3. AFNetworking源码探究（三） —— GET请求实现之任务进度设置和通知监听（一）
4. AFNetworking源码探究（四） —— GET请求实现之代理转发思想（一）
5. AFNetworking源码探究（五） —— AFURLSessionManager中NSURLSessionDelegate详细解析（一）
回顾
上一篇主要讲了NSURLSessionDelegate中的三个代理方法，讲述了它们的使用场景以及用法，这一篇主要讲AFURLSessionManager中代理NSURLSessionTaskDelegate详细解析。
1. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task willPerformHTTPRedirection:(NSHTTPURLResponse *)response newRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURLRequest *))completionHandler
首先看一下系统的API接口
/* An HTTP request is attempting to perform a redirection to a different
* URL. You must invoke the completion routine to allow the
* redirection, allow the redirection with a modified request, or
* pass nil to the completionHandler to cause the body of the redirection
* response to be delivered as the payload of this request. The default
* is to follow redirections.
*
* For tasks in background sessions, redirections will always be followed and this method will not be called.
*/
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
willPerformHTTPRedirection:(NSHTTPURLResponse *)response
newRequest:(NSURLRequest *)request
completionHandler:(void (^)(NSURLRequest * _Nullable))completionHandler;
下面看一下AFN中该代理方法的实现
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
willPerformHTTPRedirection:(NSHTTPURLResponse *)response
newRequest:(NSURLRequest *)request
completionHandler:(void (^)(NSURLRequest *))completionHandler
{
NSURLRequest *redirectRequest = request;
if (self.taskWillPerformHTTPRedirection) {
redirectRequest = self.taskWillPerformHTTPRedirection(session, task, response, request);
}
if (completionHandler) {
completionHandler(redirectRequest);
}
}
这里，主要做了下面几个逻辑：
- 如果有对应的block
taskWillPerformHTTPRedirection，那么就调用self.taskWillPerformHTTPRedirection(session, task, response, request)，返回一个新的request。 - 接着就是利用生成的request重新请求
if (completionHandler) {
completionHandler(redirectRequest);
}
- 这个方法是在服务器去重定向的时候，才会被调用。
- 此方法只会在
default session或者ephemeral session中调用，而在background session中，session task会自动重定向。 - 补充一点，初始化
NSURLSession对象的时候需要使用NSURLSessionConfiguration。有三个类工厂方法：-
+ defaultSessionConfiguration返回一个标准的 configuration，具有相同的共享NSHTTPCookieStorage，共享NSURLCache和共享NSURLCredentialStorage。 -
+ ephemeralSessionConfiguration返回一个预设配置，这个配置中不会对缓存，Cookie 和证书进行持久性的存储。这对于实现像秘密浏览这种功能来说是很理想的。 -
+ backgroundSessionConfiguration:(NSString *)identifier的独特之处在于，它会创建一个后台 session。后台 session 不同于常规的，普通的 session，它甚至可以在应用程序挂起，退出或者崩溃的情况下运行上传和下载任务。初始化时指定的标识符，被用于向任何可能在进程外恢复后台传输的守护进程（daemon）提供上下文。
-
2. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler
首先看一下苹果的API接口
/* The task has received a request specific authentication challenge.
* If this delegate is not implemented, the session specific authentication challenge
* will *NOT* be called and the behavior will be the same as using the default handling
* disposition.
*/
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler;
下面看一下AFN中该方法的实现
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler
{
NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
__block NSURLCredential *credential = nil;
if (self.taskDidReceiveAuthenticationChallenge) {
disposition = self.taskDidReceiveAuthenticationChallenge(session, task, challenge, &credential);
} else {
if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
if ([self.securityPolicy evaluateServerTrust:challenge.protectionSpace.serverTrust forDomain:challenge.protectionSpace.host]) {
disposition = NSURLSessionAuthChallengeUseCredential;
credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
} else {
disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
}
} else {
disposition = NSURLSessionAuthChallengePerformDefaultHandling;
}
}
if (completionHandler) {
completionHandler(disposition, credential);
}
}
这里我们需要知道：
- 这个是
non-session-level级别的认证 - 多了一个参数
task，然后调用我们自定义的Block会多回传这个task作为参数，这样我们就可以根据每个task去自定义我们需要的https认证方式。
3. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task needNewBodyStream:(void (^)(NSInputStream *bodyStream))completionHandler
首先看一下苹果的API接口
/* Sent if a task requires a new, unopened body stream. This may be
* necessary when authentication has failed for any request that
* involves a body stream.
*/
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
needNewBodyStream:(void (^)(NSInputStream * _Nullable bodyStream))completionHandler;
看一下AFN对该方法的实现
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
needNewBodyStream:(void (^)(NSInputStream *bodyStream))completionHandler
{
NSInputStream *inputStream = nil;
if (self.taskNeedNewBodyStream) {
inputStream = self.taskNeedNewBodyStream(session, task);
} else if (task.originalRequest.HTTPBodyStream && [task.originalRequest.HTTPBodyStream conformsToProtocol:@protocol(NSCopying)]) {
inputStream = [task.originalRequest.HTTPBodyStream copy];
}
if (completionHandler) {
completionHandler(inputStream);
}
}
该代理方法会在下面两种情况被调用
- 如果
task是由uploadTaskWithStreamedRequest:创建的，那么提供初始的request body stream时候会调用该代理方法。 - 因为认证挑战或者其他可恢复的服务器错误，而导致需要客户端重新发送一个含有
body stream的request，这时候会调用该代理。
4. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;
首先看一下苹果的API接口
/* Sent periodically to notify the delegate of upload progress. This
* information is also available as properties of the task.
*/
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didSendBodyData:(int64_t)bytesSent
totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;
看一下AFN对该方法的实现
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
didSendBodyData:(int64_t)bytesSent
totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend
{
int64_t totalUnitCount = totalBytesExpectedToSend;
if(totalUnitCount == NSURLSessionTransferSizeUnknown) {
NSString *contentLength = [task.originalRequest valueForHTTPHeaderField:@"Content-Length"];
if(contentLength) {
totalUnitCount = (int64_t) [contentLength longLongValue];
}
}
if (self.taskDidSendBodyData) {
self.taskDidSendBodyData(session, task, bytesSent, totalBytesSent, totalUnitCount);
}
}
就是每次发送数据给服务器，会回调这个方法，通知已经发送了多少。
5. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(nullable NSError *)error;
首先看一下苹果的API接口
/* Sent as the last message related to a specific task. Error may be
* nil, which implies that no error occurred and this task is complete.
*/
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didCompleteWithError:(nullable NSError *)error;
看一下AFN对该方法的实现
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];
// delegate may be nil when completing a task in the background
if (delegate) {
[delegate URLSession:session task:task didCompleteWithError:error];
[self removeDelegateForTask:task];
}
if (self.taskDidComplete) {
self.taskDidComplete(session, task, error);
}
}
这个代理就是task完成了的回调，这里涉及到task和代理的绑定与接触绑定，代码不难，就不多说了。
后记
本篇主要介绍了NSURLSessionTaskDelegate中五个代理方法的实现及其使用场景和注意事项。
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