Scrolling bottom in tableview and performance - ios

Question

I need to scroll to bottom. I have a chat app like whatsapp. So when view appears table view should show last row. I am achiving this with following line and works nice.
tableView.setContentOffset(CGPointMake(0, CGFloat.max), animated: false)
Also I need to scroll to bottom when keyboard appears. I am using Auto Layout and above line is not working. For to do this i am using following line:
func scrollToLastRow(animated: Bool) {
if self.numberOfRowsInSection(0) > 0 {
self.scrollToRowAtIndexPath(NSIndexPath(forRow: self.numberOfRowsInSection(0) - 1, inSection: 0), atScrollPosition: .Bottom, animated: animated)
}
}
This is a extension for Tableview.
This solution is working fine when there is no too much message. Then I tried with 5000 messages (so tableview have 5000 rows, but i am paging them) And when keyboard appears i see cpu usage is %98-100. I think the second code is problem for pagination, it causes loading every message to ram and my app freezes and receiving ram warning.
How to scroll to bottom without any performance issue?

Answer 1

If you have pagination, you can try to only load your current page as well as the final page, assuming you have 20 messages in each page, in this case your table have 40 rows only. Then you can use your function:
func scrollToLastRow(animated: Bool) {
if self.numberOfRowsInSection(0) > 0 {
self.scrollToRowAtIndexPath(NSIndexPath(forRow: self.numberOfRowsInSection(0) - 1, inSection: 0), atScrollPosition: .Bottom, animated: animated)
}
}

Answer 2

try this method :
let delay = 0.1 * Double(NSEC_PER_SEC)
let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))
dispatch_after(time, dispatch_get_main_queue(), {
let numberOfSections = self.tableView.numberOfSections
let numberOfRows = self.tableView.numberOfRowsInSection(numberOfSections-1)
if numberOfRows > 0 {
let indexPath = NSIndexPath(forRow: numberOfRows-1, inSection: (numberOfSections-1))
self.tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)
}
})

Answer 3

If your are creating IM app. I recommend you reverse the tableView.
So the first row appears at bottom, and don't needs scrolling at beginning anymore.
Here is a cocoapod could help: https://github.com/marty-suzuki/ReverseExtension
If you stil want to scroll to specific row
implement the UIScrollViewDelegate.scrollViewDidEndScrollingAnimation.
and goes like this.
func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
if scrollView.contentSize.height > lastContentHeight {
self.tableView.scrollToBottom()
self.lastContentHeight = scrollView.contentSize.height
}
}