iOS7带来NSURLSession
了NSURLSessionConfigure
,我们可以自定义URLCache,所以我尝试了,但没有运气,似乎我的URLCache根本没用过.
- (void)testURLCache { NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration]; config.requestCachePolicy = NSURLRequestUseProtocolCachePolicy; NSURLCache *cache = [[NSURLCache alloc] initWithMemoryCapacity:1024 * 100 diskCapacity:1024 * 100 diskPath:@"test.urlcache"]; NSLog(@"usage:%lu", (unsigned long)[cache currentDiskUsage]); config.URLCache = cache; NSURLSession *session = [NSURLSession sessionWithConfiguration:config]; for (int i = 0; i < 40; i++) { NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://ajax.googleapis.com/ajax/libs/angularjs/1.2.6/angular.min.js?%d", i]]]; NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (error) { NSLog(@"error:%@", error); } else { NSLog(@"done:%d", i); } }]; [task resume]; [NSThread sleepForTimeInterval:0.5]; } NSLog(@"usage:%lu", (unsigned long)[cache currentDiskUsage]); }
我观察到的东西:
1)一个test.urlcache
文件夹下创建Caches
文件夹,并用3个文件Cache.db
,Cache.db-shm
,Cache.db-wal
,的大小Cache.db
是4KB,在它没有记录.
2)每次运行代码时,第一次使用输出始终为0,在循环结束后,使用量变为4096,下次使用次数再次变为0.
似乎有两个潜在的问题:
你的缓存太小了.从历史上看,如果缓存的项超过总缓存大小的10%,则不会缓存.
您在最后一次请求后0.5秒检查磁盘使用情况.将缓存写入持久存储可能为时尚早.
下面我使用更大的缓存并在最终检查磁盘使用情况之前等待10秒,缓存工作正常.我还使用GCD对串行任务进行排队,以消除任意0.5秒延迟,这更加安全,并且当它通过网络检索数据以及何时使用缓存时更加明显.
- (void)testURLCache { NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration]; config.requestCachePolicy = NSURLRequestUseProtocolCachePolicy; // this is too small and won't cache // NSURLCache *cache = [[NSURLCache alloc] initWithMemoryCapacity:100 * 1024 diskCapacity:100 * 1024 diskPath:@"small.urlcache"]; // use bigger cache NSURLCache *cache = [[NSURLCache alloc] initWithMemoryCapacity:10 * 1024 * 1024 diskCapacity:20 * 1024 * 1024 diskPath:@"big.urlcache"]; config.URLCache = cache; // I'm going to add tasks to serial queue so that (a) I don't block main queue; // and (b) I don't need arbitrary delay, but I can just signal when it's done. dispatch_queue_t queue = dispatch_queue_create("com.domain.app.datatasks", 0); NSURLSession *session = [NSURLSession sessionWithConfiguration:config]; for (int i = 0; i < 40; i++) { dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); dispatch_async(queue, ^{ NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://ajax.googleapis.com/ajax/libs/angularjs/1.2.6/angular.min.js?%d", i]]]; NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (error) { NSLog(@"error:%@", error); } else { NSLog(@"done:%d", i); } dispatch_semaphore_signal(semaphore); // signal dispatched block that request is done }]; [task resume]; dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); // wait until task is complete }); } // when the queued tasks finish, then check disk usage both immediately and 10 seconds later dispatch_async(queue, ^{ // check cache size immediately after the data tasks finish NSLog(@"usage:%lu", (unsigned long)[cache currentDiskUsage]); // check again in 10 seconds double delayInSeconds = 10.0; dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC)); dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ NSLog(@"usage:%lu", (unsigned long)[cache currentDiskUsage]); }); }); }
顺便说一句,对于像这样的网络任务,我通常使用操作队列而不是调度队列,然后将我的数据任务包装在并发NSOperation
子类中.然后我可以使用依赖关系来指示最终的完成操作,但同时它们都允许并发,但也决定了并发度,但这似乎超出了原始问题的范围,我希望尽可能简单.