SDWebImage-01

SDWebImage默认沙盒缓存时长是一个星期，单位是秒（second）;

 1 // 当app接收到内存警告
 2 - (void)applicationDidReceiveMemoryWarning:(UIApplication *)application
 3 {
 4     SDWebImageManager *mgr = [SDWebImageManager sharedManager];
 5     
 6     // 1,取消正在下载对操作
 7     [mgr cancelAll];
 8     
 9     // 2,清除内存缓存
10     [mgr.imageCache clearMemory];
11     
12 //    mgr.imageCache.maxCacheAge = 1 * 24 * 60 * 60 * 7; // one week
13 //    mgr.imageCache.maxCacheSize // bytes
14 }