How to retrieve continuous data from mysql - ios

Question

I'm trying to find tutorials or examples on how to load a tableView or collectionView for continuous scrolling.
For example, I have a database of over 1000 entries but I only want to fetch a 100 at a time. Then when the scroll reaches the bottom it automatically loads the next 100, and so on...
Does anyone know of any tutorials or examples?
I'm coding using swift 2 but any objective-C examples would be fine as I can usually figure out the translation.
I have created a test app to try it out. It fetches 20 records starting from zero.
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{
#IBOutlet weak var personTable: UITableView!
var people = []
var startIndex:Int = 0;
override func viewDidLoad() {
super.viewDidLoad()
self.personTable.delegate = self
self.personTable.dataSource = self
fetchData()
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.people.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("personCell") as! TableViewCell
cell.usernameLabel.text = people[indexPath.row]["username"] as? String
return cell
}
func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
if indexPath.row == people.count - 1{
self.startIndex += 20
fetchData()
}
}
func fetchData(){
let post = PostService()
let data = ["startIndex":String(self.startIndex),"limit":"20"]
let url = "http://**********/index.php?action=fetchPersonList"
post.post(data, url: url) { (succeeded, msg) -> () in
if succeeded{
if msg as! String != "<null>"{
self.people = msg as! NSArray
self.personTable.reloadData()
}
}
}
}
}
it works when the last cell is reached and reloads the data but doesn't stop until all the rows have been downloaded which is when it throws an error as there is no more data.
I'm not sure where to go from here.
I've looked for the last couple of hours online to try and find examples but either i'm not using the right search terms or there aren't that many out there.

Answer 1

After several hours of experimenting with this (that I was hoping to avoid by finding a tutorial which wasn't to be.) I eventually found a method that works.
This is the code that works for me.
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{
#IBOutlet weak var personTable: UITableView!
var people = [NSDictionary]()
var page = 0
var holdPage = false;
override func viewDidLoad() {
super.viewDidLoad()
self.personTable.delegate = self
self.personTable.dataSource = self
fetchData()
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.people.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("personCell") as! TableViewCell
cell.usernameLabel.text = people[indexPath.row]["username"] as? String
return cell
}
func scrollViewDidScroll(scrollView: UIScrollView) {
let actualPosition:CGFloat = scrollView.contentOffset.y;
let contentHeight:CGFloat = scrollView.contentSize.height
let viewHeight:CGFloat = scrollView.frame.height
if (actualPosition + viewHeight >= contentHeight && self.holdPage == false && self.page < 3) {
self.holdPage = true //this is used to stop this if statement from running more than once.
self.page++
self.fetchData()
}
}
func fetchData(){
let post = PostService()
let startIndex = self.page * 20
let data = ["startIndex":String(startIndex),"limit":"20"]
let url = "http://*********/index.php?action=fetchPersonList"
post.post(data, url: url) { (succeeded, msg) -> () in
if succeeded{
if let data = msg as? [NSDictionary]{
self.people = self.people + data
self.holdPage = false
self.personTable.reloadData()
}
}
}
}
}
I had to use the holdPage variable as I found that when the scroll reached the end it loaded several pages in one go.
The only drawback to this method is that it keeps adding rows to the people array as you scroll down making it bigger each time. I was initially looking to remove the rows that were no longer in view but that was proving to be very complex.
Unless someone can show me a good example?