Swift-UITableView滚动到底部很慢

Question

Problem

scrolling to the bottom of table view is slow the table view contains about 25 items and there is a bit of complexity in creating each cell so creating 25 of them at the same time takes about 200 ms(believe me there is no way I can make it any more optimized)

Soloutions I've tried

there are basically two options for scrolling to bottom of table view(And I have searched the entire stack over flow for this)

1. tableView.scrollRectToVisible OR tableView.setContentOffset
2. tableView.scrollToRowAtIndexPath

the problem with the first option is, although it is pretty fast and it doesn't recreate every cell in the way from top to bottom of tableView, I need to call a new main queue to get it to work. if I call it in the same queue as the one that called tableView.reloadData() , then there will be a strange lag when scrolling the tableview(logs show that lots of cells are being re created unnecessarily, and I mean lots of them). and let me add that both threads are main thread. but still I must call the dispatch_get_main_queue() to get rid of that awkward lag. however new main thread adds a good delay to the initial load.
here is my code:

func loadData(groupID: String){
    self._chats = self._cache[groupID]!
    _tableView.reloadData()
    dispatch_async(dispatch_get_main_queue()) {
        let rect = CGRect(x: 0, y: self._tableView.contentSize.height - self._tableView.bounds.height, width: self._tableView.contentSize.width, height: self._tableView.bounds.height)
        self._tableView.scrollRectToVisible(rect, animated: false)
    }
}

again if I don't use the dispatch_get_main_queue() the tableView would be supper laggy. and if I do use it, then there will be about 100 ms delay in execution which makes the initial loading slow.

the second option is slow too, cause scrolling to the last indexPath means creating every cell in the way. and that cannot happen in the background and doing it in the main thread means freezing the UI for about 200 ms.

can you suggest any other solution or find something wrong with what I'm doing? I've tried every thing and still tableView isn't fast enough.

Answer 1

您可以使用Xcode Instruments之一的Time Profiler来了解您的应用堆栈在哪个进程上。