swift parse query limit - swift

Question

Got a question about parse query.limit with swift
using below settings and limit to pull objects from parse
func getUsernames()
query.limit = self.limit
query.findObjectsInBackgroundWithBlock //display on TableView
self.usernamesArray.append(someuser)
self.tableView.reloadData()
}
then in tableView:willDisplayCell
if indexPath.row == self.usernamesArray.count - 1 {
self.limit += 5
self.getUsernames()
}
and in viewDidAppear
if self.usernames.count == 0 {
self.limit = self.limit + 10
self.getUsernames()
}
this works fine. whenever my table scrolls through the second last Cell another 5 is ready which is what i expected yay!.
problem is if usernamesArray.count has total value of 50 and when the last cell(50th cell/count) has reached/scrolled the tableView:willDisplayCell is keep getting called and the self.limit is keep increasing 55, 60, 65 etc .... it doesn't stop when it reaches the LAST Cell or Last data in array. it keeps using the LTE data and query.limit number increases 5 by 5 (when there isn't anymore array value available)
am i doing this right? or should i try different approach?
any master of swift will be appreciated! Thanks

Answer 1

No, you aren't doing it right. First, by just increasing the limit and querying you're always getting another copy of the data you already have and maybe a few additional items. You should be changing the offset (skip) for each new query, not the limit.
You also need to check the response to see how many items were returned. If the number of items returned is less than the request limit then you know you're at the end of the data and you shouldn't make any more requests. Set a flag so that when scrolling you know there isn't anything else you can load.

Answer 2

I found it easier to create a resultSet class that handles all this information.
class ParseResultSet: NSObject {
var limit = 20
var skip = 0
var total = 0
var limitReached = false
var orderByAscendingKey: String?
var orderByDescendingKey: String?
var searchActive: Bool?
func increaseSkipByLimit() {
skip += limit
}
func increaseTotal(byNumber: Int) {
total += byNumber
if byNumber == 0 {
self.limitHasBeenReached()
skip = total
}
else {
self.increaseSkipByLimit()
}
}
func limitHasBeenReached() {
limitReached = true
}
}
I then use a method where I get the objects from Parse in a completion block. I check if the limit has been reached and increment the total if it hasn't
func getObjects(classname: String, include: [String], completion: #escaping (_ result: [PFObject]) -> Void) {
if self.resultSet.limitReached == false || self.resultSet.searchActive == true {
fetchObjectsFromClass(parseClass: classname, include: include, completion: { [weak self] (objects) in
self?.resultSet.increaseTotal(byNumber: objects.count)
completion(objects)
})
}
else {
print("LIMIT REACHED")
}
}
In my case, the fetchObjectsFromClass is a global function where the query is generated and returns an array of PFObjects.
Hopefully this gives you an idea of what you need to do