GFFImageDownLoadManager.h中創建一個類對象的入口
+ (instancetype)shareImageDownLoadManager;
GFFImageDownLoadManager.m中具體的實現方法
+ (instancetype)shareImageDownLoadManager
{
static id instance;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[GFFImageDownLoadManager alloc]init];
});
return instance;
}