UITableView performance problems in Swift - ios

Question

I'm creating a simple messenger app and using uitableview to display messages. I have created two XIB files for two types of cells i.e. incoming and outgoing. Also I have added constraints to each cell to make textViews to be not at full width of the screen (picture below)
The problem is, when i scroll table view up and down i see some jumps of content (i.e. bad performance). I made all views opaque, but it didn't help. As data storage i'm using Realm.io, to fetch messages from it. I get group_key, and list messages in this group.
Here's my code:
extension MessageChatViewController : UITableViewDataSource {
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
var count = 0
if !groupKey.isEmpty {
let messagesForGroupInRealm = realm.objects(Messages).filter("group_key = '\(groupKey)'")
if messagesForGroupInRealm.count != 0 {
count += messagesForGroupInRealm.count
}
}
return count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let messagesForGroupInRealm = messagesForCurrentChat.sorted("created_at", ascending: true)
if messagesForGroupInRealm.count != 0 {
if indexPath.row < messagesForGroupInRealm.count {
let message = messagesForGroupInRealm[indexPath.row]
if message.owner_key == gCredentials["account_key"] {
let cell = tableView.dequeueReusableCellWithIdentifier("OutgoingChatMessageCell", forIndexPath: indexPath) as! OutgoingChatMessageCell
cell.outgoingTextView.text = message.content
cell.outgoingTextView.font = UIFont(name: "NotoSans", size: 16)
return cell
} else {
let cell = tableView.dequeueReusableCellWithIdentifier("IncomingChatMessageCell", forIndexPath: indexPath) as! IncomingChatMessageCell
cell.incomingTextView.text = message.content
cell.incomingTextView.font = UIFont(name: "NotoSans", size: 16)
return cell
}
}
}
return UITableViewCell()
}
}
I also use dynamic height of cells:
override func viewDidLoad() {
super.viewDidLoad()
....
tableView.registerNib(UINib(nibName: "OutgoingChatMessageCell", bundle: nil), forCellReuseIdentifier: "OutgoingChatMessageCell")
tableView.registerNib(UINib(nibName: "IncomingChatMessageCell", bundle: nil), forCellReuseIdentifier: "IncomingChatMessageCell")
....
tableView.rowHeight = UITableViewAutomaticDimension
tableView.estimatedRowHeight = 44.0
....
}
func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return UITableViewAutomaticDimension
}
So is there any way to get best performance for tableView? Maybe i need somehow cache something ?:) Or maybe i made some mistake... Thanks for any advices (for Obj-C also)!

Answer 1

I seems like you are re-querying and sorting the entire dataset every time you draw a cell (or get a count). That would be a lot of unneeded overhead and could easily slow things down.
Why don't you make messagesForGroupInRealm a class member? Then you only have to do the query once (on init), and can then just keep accessing it directly from there.