1：類圖介紹

在AFHTTPSessionManager 初始化方法中可以看到 AFNetworking 預設使用的網路請求序列化類是AFHTTPRequestSerializer，一下是關於它的類圖：

2：類功能分析：

 一：初始化函式：

- (instancetype)init {
    self = [super init];
    if (!self) {
        return nil;
    }

    ①
    
    self.stringEncoding = NSUTF8StringEncoding;

    ②

    self.mutableHTTPRequestHeaders = [NSMutableDictionary dictionary];
    self.requestHeaderModificationQueue = dispatch_queue_create("requestHeaderModificationQueue", DISPATCH_QUEUE_CONCURRENT);
    // Accept-Language HTTP Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
    NSMutableArray *acceptLanguagesComponents = [NSMutableArray array];
    [[NSLocale preferredLanguages] enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        float q = 1.0f - (idx * 0.1f);
        [acceptLanguagesComponents addObject:[NSString stringWithFormat:@"%@;q=%0.1g", obj, q]];
        *stop = q <= 0.5f;
    }];
    [self setValue:[acceptLanguagesComponents componentsJoinedByString:@", "] forHTTPHeaderField:@"Accept-Language"];

    ③

    NSString *userAgent = nil;
#if TARGET_OS_IOS
    // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
    userAgent = [NSString stringWithFormat:@"%@/%@ (%@; iOS %@; Scale/%0.2f)☺", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[UIDevice currentDevice] model], [[UIDevice currentDevice] systemVersion], [[UIScreen mainScreen] scale]];
#elif TARGET_OS_WATCH
    // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
    userAgent = [NSString stringWithFormat:@"%@/%@ (%@; watchOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[WKInterfaceDevice currentDevice] model], [[WKInterfaceDevice currentDevice] systemVersion], [[WKInterfaceDevice currentDevice] screenScale]];
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
    userAgent = [NSString stringWithFormat:@"%@/%@ (Mac OS X %@)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[NSProcessInfo processInfo] operatingSystemVersionString]];
#endif
    
    if (userAgent) {

        
        if (![userAgent canBeConvertedToEncoding:NSASCIIStringEncoding]) {
            NSMutableString *mutableUserAgent = [userAgent mutableCopy];
            if (CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)) {
                userAgent = mutableUserAgent;
            }
        }
        [self setValue:userAgent forHTTPHeaderField:@"User-Agent"];
    }

    ④

    // HTTP Method Definitions; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
    self.HTTPMethodsEncodingParametersInURI = [NSSet setWithObjects:@"GET", @"HEAD", @"DELETE", nil];

    ⑤

    self.mutableObservedChangedKeyPaths = [NSMutableSet set];
    for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
            [self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:AFHTTPRequestSerializerObserverContext];
        }
    }
    return self;
}
 

①：設定預設的編碼格式是utf8

②：根據系統的語言設定http請求頭欄位Accept-Language 的值，eg(zh-CN;q=0.8) 解釋後面的q表示前面語言的權值，如果是多種語言，伺服器可以根據圈值的大小優先響應哪種請求。具體含義可參見文章

③：這個步驟的操作意思是刪除user-agent 中所有的不能ascii編碼的字元，詳細的函式介紹：

CFStringTransform(CFMutableStringRef string, CFRange *range, CFStringRef transform, Boolean reverse)對於此函式的詳細介紹可參考文章，下面我將使用例項介紹此函式的威力，拿AFNetworking中使用舉例。

   1:將中文變成漢語拼音帶音調程式碼如下：

NSString *userAgent = @"中華人民共和國";
    NSMutableString *mutableUserAgent = [userAgent mutableCopy];
    CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin", false);
    NSLog(@"%@",mutableUserAgent);

2016-12-06 21:06:38.925 test2[15785:400567] zhōng huá rén mín gòng hé guó
 

 NSString *userAgent = @"中華人民共和國";
    NSMutableString *mutableUserAgent = [userAgent mutableCopy];
    CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII", false);
    NSLog(@"%@",mutableUserAgent);
    NSLog(@"%@",userAgent);

2016-12-06 21:09:41.519 test2[15858:404061] zhong hua ren min gong he guo

輸出結果：

2016-12-06 21:12:38.127 test2[15936:407291] 1Aa3

4：AFNetworking的使用解釋：

CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)

2016-12-06 21:44:40.206 test2[16642:436125] 1Aa a3zhong hua ren min gong he guo

④：http請求方法中 GET HEAD DELETE 此三種方法是對引數直接放在URI中，因此需要設定，對這幾種方式請求的引數編碼

⑤：主要是對系統的函式的監聽（KVO）系統的函式如下程式碼（_AFHTTPRequestSerializerObservedKeyPaths）：

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;
}