swift 异步组执行

/// 缓存图片

  private func cacheImages(viewModels : [StatusViewModel]) {

    // 0.创建group

    let group = dispatch_group_create()

   

    // 1.缓存图片

    for viewmodel in viewModels {

      for picURL in viewmodel.picURLs {

        dispatch_group_enter(group)

        SDWebImageManager.sharedManager().downloadImageWithURL(picURL,options: [],progress: nil,completed: { (_,_,_) -> Void in

          dispatch_group_leave(group)

        })

      }

    }

   

    // 2.刷新表格

    dispatch_group_notify(group,dispatch_get_main_queue()) { () -> Void in

      self.tableView.reloadData()

    }

  }