版本記錄

前言

我們做APP發(fā)起網(wǎng)絡(luò)請(qǐng)求翰苫，都離不開一個(gè)非常有用的框架AFNetworking育拨，可以說這個(gè)框架的知名度已經(jīng)超過了蘋果的底層網(wǎng)絡(luò)請(qǐng)求部分谨履，很多人可能不知道蘋果底層是如何發(fā)起網(wǎng)絡(luò)請(qǐng)求的，但是一定知道AFNetworking熬丧，接下來幾篇我們就一起詳細(xì)的解析一下這個(gè)框架笋粟。感興趣的可以看上面寫的幾篇。
1. AFNetworking源碼探究（一） —— 基本介紹
2. AFNetworking源碼探究（二） —— GET請(qǐng)求實(shí)現(xiàn)之NSURLSessionDataTask實(shí)例化（一）
3. AFNetworking源碼探究（三） —— GET請(qǐng)求實(shí)現(xiàn)之任務(wù)進(jìn)度設(shè)置和通知監(jiān)聽（一）
4. AFNetworking源碼探究（四） —— GET請(qǐng)求實(shí)現(xiàn)之代理轉(zhuǎn)發(fā)思想（一）
5. AFNetworking源碼探究（五） —— AFURLSessionManager中NSURLSessionDelegate詳細(xì)解析（一）
6. AFNetworking源碼探究（六） —— AFURLSessionManager中NSURLSessionTaskDelegate詳細(xì)解析（一）

回顧

上一篇主要介紹了NSURLSessionTaskDelegate中五個(gè)代理方法的實(shí)現(xiàn)及其使用場(chǎng)景和注意事項(xiàng)析蝴。這一篇主要介紹NSURLSessionDataDelegate幾個(gè)代理方法害捕。

1. - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler;

首先看一下蘋果該方法的API

/* The task has received a response and no further messages will be
 * received until the completion block is called. The disposition
 * allows you to cancel a request or to turn a data task into a
 * download task. This delegate message is optional - if you do not
 * implement it, you can get the response as a property of the task.
 *
 * This method will not be called for background upload tasks (which cannot be converted to download tasks).
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                 didReceiveResponse:(NSURLResponse *)response
                                  completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler;

看一下AFN中該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
 completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler
{
    NSURLSessionResponseDisposition disposition = NSURLSessionResponseAllow;

    if (self.dataTaskDidReceiveResponse) {
        disposition = self.dataTaskDidReceiveResponse(session, dataTask, response);
    }

    if (completionHandler) {
        completionHandler(disposition);
    }
}

這里，NSURLSessionResponseDisposition disposition = NSURLSessionResponseAllow;表示默認(rèn)為繼續(xù)進(jìn)行嫌变。

• completionHandler這個(gè)block吨艇，通過傳入一個(gè)類型為NSURLSessionResponseDisposition的變量來決定該傳輸任務(wù)接下來該做什么：

  • NSURLSessionResponseAllow 該task正常進(jìn)行
  • NSURLSessionResponseCancel 該task會(huì)被取消
  • NSURLSessionResponseBecomeDownload 會(huì)調(diào)用URLSession:dataTask:didBecomeDownloadTask:方法來新建一個(gè)download task以代替當(dāng)前的data task
  • NSURLSessionResponseBecomeStream 轉(zhuǎn)成一個(gè)StreamTask

• 當(dāng)你把添加content-type的類型為multipart/x-mixed-replace那么服務(wù)器的數(shù)據(jù)會(huì)分片的傳回來。然后這個(gè)方法是每次接受到對(duì)應(yīng)片響應(yīng)的時(shí)候會(huì)調(diào)被調(diào)用腾啥。你應(yīng)該在這個(gè)函數(shù)中合理地處理先前的數(shù)據(jù)东涡，否則會(huì)被新數(shù)據(jù)覆蓋。

2. - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask;

首先看一下蘋果該方法的API

/* Notification that a data task has become a download task.  No
 * future messages will be sent to the data task.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                              didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask;

看一下AFN中該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask
{
    AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
    if (delegate) {
        [self removeDelegateForTask:dataTask];
        [self setDelegate:delegate forTask:downloadTask];
    }

    if (self.dataTaskDidBecomeDownloadTask) {
        self.dataTaskDidBecomeDownloadTask(session, dataTask, downloadTask);
    }
}

當(dāng)代理1方法中的disposition = NSURLSessionResponseBecomeDownload的時(shí)候倘待，就會(huì)調(diào)用這個(gè)方法疮跑。

這個(gè)代理方法是被上面的代理方法觸發(fā)的，作用就是新建一個(gè)downloadTask凸舵，替換掉當(dāng)前的dataTask祖娘。所以我們?cè)谶@里做了AF自定義代理的重新綁定操作[self setDelegate:delegate forTask:downloadTask];。

3. - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data

首先看一下蘋果該方法的API

/* Sent when data is available for the delegate to consume.  It is
 * assumed that the delegate will retain and not copy the data.  As
 * the data may be discontiguous, you should use 
 * [NSData enumerateByteRangesUsingBlock:] to access it.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                     didReceiveData:(NSData *)data;

看一下AFN中該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
    didReceiveData:(NSData *)data
{

    AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
    [delegate URLSession:session dataTask:dataTask didReceiveData:data];

    if (self.dataTaskDidReceiveData) {
        self.dataTaskDidReceiveData(session, dataTask, data);
    }
}

• 獲取到數(shù)據(jù)就會(huì)調(diào)用啊奄，會(huì)被反復(fù)調(diào)用渐苏，請(qǐng)求到的數(shù)據(jù)就在這被拼裝完整。
• 這個(gè)方法和上面didCompleteWithError算是NSURLSession的代理中最重要的兩個(gè)方法菇夸。
• 我們轉(zhuǎn)發(fā)了這個(gè)方法到AF的代理中去琼富，所以數(shù)據(jù)的拼接都是在AF的代理中進(jìn)行的。這也是情理中的庄新，畢竟每個(gè)響應(yīng)數(shù)據(jù)都是對(duì)應(yīng)各個(gè)task鞠眉，各個(gè)AF代理的薯鼠。在AFURLSessionManager都只是做一些公共的處理。

4. - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask willCacheResponse:(NSCachedURLResponse *)proposedResponse completionHandler:(void (^)(NSCachedURLResponse * _Nullable cachedResponse))completionHandler;

首先看一下蘋果該方法的API

/* Invoke the completion routine with a valid NSCachedURLResponse to
 * allow the resulting data to be cached, or pass nil to prevent
 * caching. Note that there is no guarantee that caching will be
 * attempted for a given resource, and you should not rely on this
 * message to receive the resource data.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                  willCacheResponse:(NSCachedURLResponse *)proposedResponse 
                                  completionHandler:(void (^)(NSCachedURLResponse * _Nullable cachedResponse))completionHandler;

看一下AFN中該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
          dataTask:(NSURLSessionDataTask *)dataTask
 willCacheResponse:(NSCachedURLResponse *)proposedResponse
 completionHandler:(void (^)(NSCachedURLResponse *cachedResponse))completionHandler
{
    NSCachedURLResponse *cachedResponse = proposedResponse;

    if (self.dataTaskWillCacheResponse) {
        cachedResponse = self.dataTaskWillCacheResponse(session, dataTask, proposedResponse);
    }

    if (completionHandler) {
        completionHandler(cachedResponse);
    }
}

• 該方法的作用就是詢問data task或上傳任務(wù)（upload task）是否緩存response械蹋。
• 當(dāng)task接收到所有期望的數(shù)據(jù)后出皇，session會(huì)調(diào)用此代理方法。
• 當(dāng)task接收到所有期望的數(shù)據(jù)后哗戈，session會(huì)調(diào)用此代理方法郊艘。如果你沒有實(shí)現(xiàn)該方法，那么就會(huì)使用創(chuàng)建session時(shí)使用的configuration對(duì)象決定緩存策略唯咬。這個(gè)代理方法最初的目的是為了阻止緩存特定的URLs或者修改NSCacheURLResponse對(duì)象相關(guān)的userInfo字典暇仲。
• 該方法只會(huì)當(dāng)request決定緩存response時(shí)候調(diào)用。作為準(zhǔn)則副渴，responses只會(huì)當(dāng)以下條件都成立的時(shí)候返回緩存：
  • 該request是HTTP或HTTPS URL的請(qǐng)求（或者你自定義的網(wǎng)絡(luò)協(xié)議奈附，并且確保該協(xié)議支持緩存）
  • 確保request請(qǐng)求是成功的（返回的status code為200-299）
  • 返回的response是來自服務(wù)器端的，而非緩存中本身就有的
  • 提供的NSURLRequest對(duì)象的緩存策略要允許進(jìn)行緩存
  • 服務(wù)器返回的response中與緩存相關(guān)的header要允許緩存
  • 該response的大小不能比提供的緩存空間大太多（比如你提供了一個(gè)磁盤緩存煮剧，那么response大小一定不能比磁盤緩存空間還要大5%）

后記

本篇主要介紹了NSURLSessionDataDelegate中四個(gè)代理方法的實(shí)現(xiàn)及其使用場(chǎng)景和注意事項(xiàng)斥滤。