1.示范文檔

首先看iOS Example

打開(kāi)Appdelegate文件

第一行代碼是

NSURLCache *URLCache = [[NSURLCache alloc] initWithMemoryCapacity:4 * 1024 * 1024 diskCapacity:20 * 1024 * 1024 diskPath:nil];

[NSURLCache setSharedURLCache:URLCache];

這個(gè)緩存類(lèi)以前沒(méi)有注意過(guò)，也沒(méi)有用過(guò)，打開(kāi)幫助文檔看看

Description:
Initializes an NSURLCache object with the specified values.(初始化一個(gè)NSURLCache實(shí)例)

Parameters:（參數(shù)）
memoryCapacity:The memory capacity of the cache, in bytes.
（內(nèi)存緩存的容量：?jiǎn)挝粸閎ytes）
diskCapacity:The disk capacity of the cache, in bytes.
（硬盤(pán)緩存的容量：?jiǎn)挝粸閎ytes）
path:In OS X, path is the location at which to store the on-disk cache.
In iOS, path is the name of a subdirectory of the application’s default cache directory in which to store the on-disk cache (the subdirectory is created if it does not exist).
OS X存儲(chǔ)路徑在硬盤(pán) cache文件夾
iOS：在應(yīng)用的默認(rèn)cache文件夾子目錄下，如果子目錄不存在時(shí)會(huì)創(chuàng)建一個(gè)新的
創(chuàng)建了網(wǎng)絡(luò)緩存實(shí)例，內(nèi)存緩存4M, 硬盤(pán)緩存為20M，路徑為默認(rèn)nil

這個(gè)日后再深入研究吧，不知道內(nèi)存、硬盤(pán)都滿(mǎn)了會(huì)發(fā)生什么情況

再看下面一句

[[AFNetworkActivityIndicatorManager sharedManager] setEnabled:YES];

屬于UIKit+AFNetworking里面的類(lèi)
點(diǎn)進(jìn)去發(fā)現(xiàn)注釋非常詳細(xì)，都是英文，慢慢啃吧

AFNetworkActivityIndicatorManager manages the state of the network activity indicator in the status bar. When enabled, it will listen for notifications indicating that a session task has started or finished, and start or stop animating the indicator accordingly. The number of active requests is incremented and decremented much like a stack or a semaphore, and the activity indicator will animate so long as that number is greater than zero.
AFNetworkActivityIndicatorManager類(lèi)是管理狀態(tài)欄上的網(wǎng)絡(luò)指示器，就是那個(gè)會(huì)轉(zhuǎn)的小菊花。當(dāng)設(shè)置enabled屬性為YES，它會(huì)接受session task（會(huì)話(huà)層任務(wù)？）的通知，當(dāng)任務(wù)結(jié)束、開(kāi)始或則指示器會(huì)相應(yīng)地以動(dòng)畫(huà)的形式開(kāi)始轉(zhuǎn)或者消失，如果網(wǎng)絡(luò)任務(wù)請(qǐng)求數(shù)量大于零，指示器將會(huì)持續(xù)轉(zhuǎn)一段時(shí)間

You should enable the shared instance of AFNetworkActivityIndicatorManager when your application finishes launching. In AppDelegate application:didFinishLaunchingWithOptions: you can do so with the following code:

[[AFNetworkActivityIndicatorManager sharedManager] setEnabled:YES];
這段話(huà)是教怎么用這個(gè)類(lèi)的，在應(yīng)用啟動(dòng)之后就在AppDelegate application:didFinishLaunchingWithOptions:方法內(nèi)調(diào)用

By setting enabled to YES for sharedManager, the network activity indicator will show and hide automatically as requests start and finish. You should not ever need to call incrementActivityCount or decrementActivityCount yourself.
只要設(shè)置enabled屬性為YES，這個(gè)類(lèi)就會(huì)自動(dòng)處理指示器出現(xiàn)和消失，不需要調(diào)用incrementActivityCount和decrementActivityCount這兩個(gè)參數(shù)

NS_EXTENSION_UNAVAILABLE_IOS("Use view controller based solutions where appropriate instead.")
iOS8新特性，擴(kuò)展，Today視圖之類(lèi)的，不能在擴(kuò)展中使用

@property (nonatomic, assign) NSTimeInterval activationDelay;
這個(gè)參數(shù)有點(diǎn)意思，按照蘋(píng)果人機(jī)交互原則，如果網(wǎng)絡(luò)請(qǐng)求過(guò)快就不需要顯示菊花轉(zhuǎn)，默認(rèn)值為1秒，這個(gè)參數(shù)猜測(cè)應(yīng)該是少于1秒的請(qǐng)求就不顯菊花，接下來(lái)在實(shí)現(xiàn)文件中再研究

@property (nonatomic, assign) NSTimeInterval completionDelay;
和activationDelay相對(duì)應(yīng)，如果有多個(gè)請(qǐng)求，指示器為了連貫，會(huì)有一個(gè)延遲消失的時(shí)間，默認(rèn)為0.17秒

- (void)setNetworkingActivityActionWithBlock:(nullable void (^)(BOOL networkActivityIndicatorVisible))block;
這個(gè)方法在指示器即將出現(xiàn)、消失時(shí)調(diào)用，調(diào)用這個(gè)方法可以通過(guò)block自定義某些邏輯，默認(rèn)是null，manager會(huì)自動(dòng)管理指示器的出現(xiàn)，消失，如果設(shè)置了block，需要手動(dòng)管理，其實(shí)就是調(diào)用系統(tǒng)的方法：[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:networkActivityIndicatorVisible];

NS_ASSUME_NONNULL_BEGIN

NS_ASSUME_NONNULL_END
蘋(píng)果為了和swift的可選類(lèi)型兼容設(shè)定的宏，用了這兩個(gè)宏，它們中間的方法參數(shù)默認(rèn)為_(kāi)_nonnull，只需要為特定的參數(shù)設(shè)置__nullable就可以了

實(shí)現(xiàn)文件：

typedef NS_ENUM(NSInteger, AFNetworkActivityManagerState) {
    AFNetworkActivityManagerStateNotActive,
    AFNetworkActivityManagerStateDelayingStart,
    AFNetworkActivityManagerStateActive,
    AFNetworkActivityManagerStateDelayingEnd
};
static NSTimeInterval const kDefaultAFNetworkActivityManagerActivationDelay = 1.0;
static NSTimeInterval const kDefaultAFNetworkActivityManagerCompletionDelay = 0.17;
按照OC規(guī)范定義了四個(gè)枚舉和兩個(gè)常量，之前所說(shuō)的按照apple人機(jī)交互原則設(shè)定

+ (instancetype)sharedManager {
    static AFNetworkActivityIndicatorManager *_sharedManager = nil;
    static dispatch_once_t oncePredicate;
    dispatch_once(&oncePredicate, ^{
        _sharedManager = [[self alloc] init];
    });

    return _sharedManager;
}
標(biāo)準(zhǔn)的單例寫(xiě)法

接下來(lái)主要探討一下網(wǎng)絡(luò)請(qǐng)求多任務(wù)下指示器的工作

- (instancetype)init {
    self = [super init];
    if (!self) {
        return nil;
    }
    self.currentState = AFNetworkActivityManagerStateNotActive;
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkRequestDidStart:) name:AFNetworkingTaskDidResumeNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkRequestDidFinish:) name:AFNetworkingTaskDidSuspendNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkRequestDidFinish:) name:AFNetworkingTaskDidCompleteNotification object:nil];
    self.activationDelay = kDefaultAFNetworkActivityManagerActivationDelay;
    self.completionDelay = kDefaultAFNetworkActivityManagerCompletionDelay;

    return self;
}
首先在初始化方法里設(shè)置了三個(gè)通知，通過(guò)currentState來(lái)控制指示器的狀態(tài)

看一下請(qǐng)求開(kāi)始的時(shí)候通知方法

1.在networkRequestDidStart:方法接收通知，驗(yàn)證請(qǐng)求地址，activityCount+1

2.主線程下更新currentState，設(shè)置開(kāi)始延時(shí)定時(shí)器[self startActivationDelayTimer]，定時(shí)器加入到NSRunLoopCommonModes的runloop

3.定時(shí)器到時(shí)方法activationDelayTimerFired，通過(guò)networkActivityOccurring(activityCount是否 > 0)屬性判斷CurrentState狀態(tài)，如果activityCount>0,把currentState設(shè)置為AFNetworkActivityManagerStateActive

4.最后通過(guò)setNetworkActivityIndicatorVisible方法展現(xiàn)指示器

請(qǐng)求結(jié)束的通知方法：

1.networkRequestDidFinish:方法接收通知，驗(yàn)證請(qǐng)求地址，activityCount－1，當(dāng)activityCount ＝＝ 0，狀態(tài)會(huì)有所變化
2.主線程下更新CurrentState，設(shè)置結(jié)束延時(shí)定時(shí)器[self startCompletionDelayTimer]，定時(shí)器加入到NSRunLoopCommonModes的runloop
3.定時(shí)器到時(shí)方法completionDelayTimerFired,調(diào)用[self setCurrentState:AFNetworkActivityManagerStateNotActive];設(shè)置currentState為無(wú)活動(dòng)
4.關(guān)閉定時(shí)器
[self cancelActivationDelayTimer]; [self cancelCompletionDelayTimer];
調(diào)用setNetworkActivityIndicatorVisible:方法使指示器菊花消失

指示器實(shí)現(xiàn)方法大概就是這樣了，順帶說(shuō)一下，session task通知是由AFURLSessionManager類(lèi)發(fā)出的異步通知

還有就是有一點(diǎn)不明白的地方，AFN使用了很多KVO手動(dòng)通知

比如說(shuō)：

[self willChangeValueForKey:@"networkActivityIndicatorVisible"];
[self didChangeValueForKey:@"networkActivityIndicatorVisible"];

這一對(duì)，但是沒(méi)有看見(jiàn)設(shè)置了觀察者和關(guān)閉自動(dòng)通知的方法。不知道設(shè)置kvo手動(dòng)通知的原因是什么