How do I update tableview cell when It had changed - swift

Question

When I scroll up&down then tableview cell has set overtimes so It affect lagging.
I want to update only when the data is updated.
Post.swift (It is model)
import Foundation
import Parse
class Post: PFObject, PFSubclassing {
#NSManaged var postBy: PFUser?
#NSManaged var postUser: String?
#NSManaged var postUserImg: PFFile?
#NSManaged var postText: String?
#NSManaged var postImg: PFFile?
#NSManaged var sell: NSNumber?
#NSManaged var commentPointer: PFObject?
#NSManaged var commentBy: String?
#NSManaged var comment: String?
#NSManaged var liked: NSArray?
#NSManaged var likeCount: NSNumber?
#NSManaged var mention: NSArray?
#NSManaged var hashtag: NSArray?
static func parseClassName() -> String {
return "Post"
}
override class func query() -> PFQuery<PFObject>? {
let query = PFQuery(className: Post.parseClassName())
return query
}
}
extension Post: FeedCellSupport {
var username:String?{
return postUser
}
var userImg:PFFile?{
return postUserImg
}
var commentText:String?{
guard let commentTxt = comment else {
return ""
}
return commentTxt
}
TableView.swift
protocol FeedCellSupport {
var postDate: String? { get }
var postId: String? { get }
var postObj: PFObject? { get }
var img: PFFile? { get }
var username:String?{ get }
var userImg:PFFile?{ get }
var commentText:String?{ get }
var commentFrom:String?{ get }
var postText: String? { get }
var likes: Int? { get }
var isLiked: Bool? { get }
var isSell: Bool? { get }
var hashtags: NSArray? { get }
var mentions: NSArray? { get }
}
func fetchObjects() {
let postQuery = Post.query()?
.whereKeyExists("objectId")
.includeKeys(["postBy", "commentPointer", "commentPointer.commentBy", "commentBy"])
.order(byDescending: "createdAt")
as! PFQuery<Post>
postQuery.limit = self.page
postQuery.cachePolicy = .networkElseCache
postQuery.findObjectsInBackground { (object:[Post]?, error:Error?) in
if error == nil {
self.results = object!
}else {
print(error?.localizedDescription as Any)
}
self.tableView.reloadData()
self.refresher.endRefreshing()
}
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "ShopDetailCell", for: indexPath) as! ShopDetailCell
if let object = results[indexPath.row] as? FeedCellSupport{
cell.postID = object.postObj!
cell.userNameLabel.text = object.username!
cell.userNameLabel.sizeToFit()
cell.descriptionLabel.text = object.postText!
cell.descriptionLabel.sizeToFit()
cell.commentByLabel.text = object.commentFrom!
cell.commentByLabel.sizeToFit()
cell.commentLabel.text = object.commentText!
cell.commentLabel.sizeToFit()
cell.delegate = self
}
return cell
}
How can I ensure that data is updated only when it changes?

Answer 1

What are your App functionalities? Your problem is associated with the way suitable to accomplish your task, that is: to update app contents.
So it is about business logic: when should the information be updated?
The solution to your problem is using user toggled events to refresh the contents or other possible solutions such as Application Delegate.
Except for these answers, the contents cannot update tableview automatically as your expectation.
Update
I considered this line of code is lagging:
if let object = results[indexPath.row] as? FeedCellSupport{
//other code
}
Because code inside these braces is dealing with data setting. You could try to mock up local data instead of this results array to say whether this is the problem.