判断缓存，
先 memory cache,
再 disk cache (NSFileManager )

/**
 *  Check if image has already been cached
 *
 *  @param url image url
 *
 *  @return if the image was already cached
 */
- (BOOL)cachedImageExistsForURL:(NSURL *)url;

/**
 *  Check if image has already been cached on disk only
 *
 *  @param url image url
 *
 *  @return if the image was already cached (disk only)
 */
- (BOOL)diskImageExistsForURL:(NSURL *)url;

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CTNetworking 分析

@interface FireSingleAPI : UIViewController

-> 遵守协议

@interface TestAPIManager : CTAPIBaseManager <CTAPIManager>

-> 继承

@interface CTAPIBaseManager : NSObject

单元测试

FireSingleAPI（FireSingleAPIViewController ）
~> 由 管理
@interface TestCaseFactory : NSObject

if (testCaseType == TestCaseTypeFireSingleAPI) {
       testCase = [[FireSingleAPI alloc] init];      //   testCase = [[FireSingleAPIViewController alloc] init];
   }

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YTKNetworking 分析

YTKNetworkingDemo

@interface UploadImageApi : YTKRequest
@interface RegisterApi : YTKRequest
@interface GetUserInfoApi : YTKRequest
@interface GetImageApi : YTKRequest
~>
@interface YTKRequest : YTKBaseRequest
~>
@interface YTKBaseRequest : NSObject

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AFN 分析

为了兼容 iOS 7 和 iOS 8的 NSURLSessionTask implementation
AFURLSessionManager.m 文件中
方法混淆

@interface _AFURLSessionTaskSwizzling : NSObject

@end

@implementation _AFURLSessionTaskSwizzling

+ (void)load {

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why excute self.session getTasksWithCompletionHandler in initWithSessionConfiguration? #3499
AFURLSessionManager
I believe this for restoring a session from the background.