Swift 1.2：UITableView.reloadData（）调用的速度不够快。 滚动之前如何确定数据已加载？

Question

I want to make sure my tableView data is fully loaded before I tell it to scroll to the last cell at the bottom. Here is the code I have:

self.tableView.reloadData()
self.tableView.scrollToRowAtIndexPath(NSIndexPath(index: (self.chatMessages.count - 1)), atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)

Which doesn't work, and only alerts the UITableView instead of calling the method. I've tried to call reloadData() from the main thread and that still doesn't work.

dispatch_async(dispatch_get_main_queue()) {
self.tableView.reloadData()
}

self.tableView.scrollToRowAtIndexPath(NSIndexPath(index: (self.chatMessages.count - 1)), atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)

How can I make this work without a SIGBART Error?

Here's my stack trace:

2015-08-11 16:31:17.026 SuperCommunication[13769:441407] *** Terminating app due to uncaught exception 'NSRangeException', reason: '-[UITableView _contentOffsetForScrollingToRowAtIndexPath:atScrollPosition:]: section (1) beyond bounds (1).'
*** First throw call stack:
(
    0   CoreFoundation                      0x0000000105316c65 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x0000000106e81bb7 objc_exception_throw + 45
    2   CoreFoundation                      0x0000000105316b9d +[NSException raise:format:] + 205
    3   UIKit                               0x0000000105ca447d -[UITableView _contentOffsetForScrollingToRowAtIndexPath:atScrollPosition:] + 429
    4   UIKit                               0x0000000105ca5338 -[UITableView scrollToRowAtIndexPath:atScrollPosition:animated:] + 33
    5   SuperCommunication                  0x0000000103f023f4 _TFC18SuperCommunication14ViewController30loadMessagesForSelectedChannelfS0_FT_T_ + 852
    6   SuperCommunication                  0x0000000103f0006d _TFC18SuperCommunication14ViewController9tableViewfS0_FTCSo11UITableView23didSelectRowAtIndexPathCSo11NSIndexPath_T_ + 973
    7   SuperCommunication                  0x0000000103f000ef _TToFC18SuperCommunication14ViewController9tableViewfS0_FTCSo11UITableView23didSelectRowAtIndexPathCSo11NSIndexPath_T_ + 79
    8   UIKit                               0x0000000105ca6d89 -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 1293
    9   UIKit                               0x0000000105ca6eca -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 219
    10  UIKit                               0x0000000105bd95ec _applyBlockToCFArrayCopiedToStack + 314
    11  UIKit                               0x0000000105bd9466 _afterCACommitHandler + 533
    12  CoreFoundation                      0x0000000105249ca7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
    13  CoreFoundation                      0x0000000105249c00 __CFRunLoopDoObservers + 368
    14  CoreFoundation                      0x000000010523fa33 __CFRunLoopRun + 1123
    15  CoreFoundation                      0x000000010523f366 CFRunLoopRunSpecific + 470
    16  GraphicsServices                    0x0000000109388a3e GSEventRunModal + 161
    17  UIKit                               0x0000000105bb58c0 UIApplicationMain + 1282
    18  SuperCommunication                  0x0000000103f0dbf7 main + 135
    19  libdyld.dylib                       0x00000001075b7145 start + 1
    20  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Answer 1

Your problem is in wrong NSIndexPath object initializer. You need to use NSIndexPath(forRow: yourRow, inSection: yourSection) :

self.tableView.reloadData()
self.tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: self.chatMessages.count - 1, inSection: 0), atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)

Update:

Maybe performing scroll after some delay will help you:

self.tableView.reloadData()
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(0.1 * Double(NSEC_PER_SEC))), dispatch_get_main_queue()) { () -> Void in
    self.tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: self.chatMessages.count - 1, inSection: 0), atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)
}

Answer 2

One possible solution would be

func tableView(tableView: UITableView!, willDisplayCell cell: UITableViewCell!, forRowAtIndexPath indexPath: NSIndexPath!) {
    if indexPath.row == self.chatMessages.count - 1 {
       //perform scroll
    }
}