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Swift4 - Pagination

- 1 answer

I'm new in developing ios app. Still dont know much. I successfully can display the articles well from first page only but fail to show other articles from other page when I scroll-up to view more. I really need help if somebody knows how to do pagination from my collection View. Below is the picture of my api that I use.

API

And below is my code where i get the data from api -- (Artikel.swift)

import Foundation
import Alamofire
import SwiftyJSON
import os.log

struct Artikel: ServiceCompletionHandler {
    static func getCategories (completionHandler: @escaping ArrayCompletionHandler) {
        let headers: HTTPHeaders = [
            "Accept": "application/json"
        ]
        let parameters: Parameters = [
            "secret_key": Config.api_key
        ]
        Alamofire.request("\(Config.server_address)/article-categories", method: .post, parameters: parameters, headers: headers)
            .responseJSON { (response) -> Void in
                switch response.result {
                case .success:
                    let json = JSON(response.result.value!)
                    if json["data"].exists() {
                        if let data = json["data"]["data"].array {
                            completionHandler(data, nil)
                        } else {
                            completionHandler([], nil)
                        }
                    } else {
                        completionHandler([], nil)
                    }
                case .failure(let error):
                    print(error)
                    completionHandler([], "Network error has occured.")
                }
        }
    }
    static func getArticles(_ category_id: Int, completionHandler: @escaping ArrayCompletionHandler) {
        let headers: HTTPHeaders = [
            "Accept": "application/json",
            "secret-key": Config.api_key]

        let value: Int = category_id
        let newcategory = String(describing: value)

//        var nextpages = NewsSectionViewController.url

        let new_api = Config.server_addforarticle + newcategory

        Alamofire.request(new_api, method: .get, headers: headers)
            .responseJSON { (response) -> Void in
                switch response.result {
                case .success:
                    let json = JSON(response.result.value!)
//                    dump(json, name: "testing")
                    if let articles = json["articles"]["data"].array {
                        completionHandler(articles, nil)

                    }else{
                        completionHandler([], nil)
                    }
                case .failure(let error):
                    print(error)
                    completionHandler([], "Network error has occured.")
                }
        }
    }
    }

and here where i display my articles. But yeah, I cant do pagination it stuck to 4-5 articles only. I just dont have any idea how to do what I did in my android version.

NewsSectionViewController.swift

import UIKit
import SwiftyJSON
import AlamofireImage

protocol NewsSectionViewControllerDelegate {
    func updateArrowPosition()
}

class NewsSectionViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    // MARK: - Variables
    var itemIndex: Int = 0
    var category:JSON!
    var stories:[JSON] = []
    var delegate: NewsSectionViewControllerDelegate?

    // MARK: - Views
    @IBOutlet var titleLabel: UILabel!
    @IBOutlet var collectionView: UICollectionView!
    @IBOutlet var loadingIndicator: UIActivityIndicatorView!

    // MARK: - Constraint
    @IBOutlet var titleTopConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        self.titleLabel.text = category["name"].stringValue.uppercased()

        self.collectionView.contentInset = UIEdgeInsetsMake(0, 0, 114, 0)
        if #available(iOS 11.0, *) {
            if ((UIApplication.shared.keyWindow?.safeAreaInsets.top)! > CGFloat(0.0)) {
                self.collectionView.contentInset = UIEdgeInsetsMake(0, 0, 173, 0)
                self.collectionView.scrollIndicatorInsets = UIEdgeInsetsMake(0, 0, 173, 0)
            }
        }

        self.loadingIndicator.startAnimating()
        Artikel.getArticles(category["id"].intValue) {
            (articles, error) in
            self.loadingIndicator.stopAnimating()
            if error == nil {
                self.stories = articles
                self.collectionView.reloadData()
            }
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    // MARK: - Collection View
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.stories.count - 1
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        var cell: NewsItemCollectionViewCell?

        let item = stories[indexPath.row + 1]

        if indexPath.row == 0 {
            cell = collectionView.dequeueReusableCell(withReuseIdentifier: "BigCell", for: indexPath) as? NewsItemCollectionViewCell
        } else {
            cell = collectionView.dequeueReusableCell(withReuseIdentifier: "SmallCell", for: indexPath) as? NewsItemCollectionViewCell
        }

        cell!.titleLabel.text = item["title"].stringValue

        if let thumbUrlString = item["banner_url_large"].string {
            if let thumbUrl = URL(string: thumbUrlString) {
                cell?.coverImageView.af_setImage(withURL: thumbUrl)
            }
        }

        let wpDateFormatter = DateFormatter()
        wpDateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"

        let dayDateFormatter = DateFormatter()
        dayDateFormatter.dateStyle = .medium
        dayDateFormatter.doesRelativeDateFormatting = true

        let date = wpDateFormatter.date(from: item["date_publish_web"].stringValue)!
        cell!.timestampLabel.text = dayDateFormatter.string(from: date)

        return cell!

    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let story = self.stories[indexPath.row + 1]

        let newsContents = self.storyboard?.instantiateViewController(withIdentifier: "NewsContent") as! NewsContentViewController
        newsContents.story = story
        newsContents.title = self.category["name"].string
        self.navigationController?.pushViewController(newsContents, animated: true)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        if indexPath.row == 0 {
            let width = UIScreen.main.bounds.width - 30
            return CGSize(width: width, height: 385 - 20)
        } else {
            let width = (UIScreen.main.bounds.width - 45) / 2
            return CGSize(width: width, height: 210)
        }

    }

    // MARK: - ScrollView
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if scrollView == self.collectionView {
            self.titleTopConstraint.constant = 30 - scrollView.contentOffset.y
        }
        if let delegate = self.delegate {
            delegate.updateArrowPosition()
        }
    }


    /*
     // MARK: - Navigation

     // In a storyboard-based application, you will often want to do a little preparation before navigation
     override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
     // Get the new view controller using segue.destinationViewController.
     // Pass the selected object to the new view controller.
     }
     */

}

Any help I really appreciated and thank you in advance :)

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Answer

In NewsSectionViewController:

1) add global variables:

a) var nextPageUrl: String? ;

b) let numberOfPagination = 5 (5 it's a number of items in one url page);

c) add variable hasMoreItems

var hasMoreItems: Bool {
    get {
        guard let count = nextPageUrl?.count, count > 0 else {
            return false
        }
        return true
    }
}

d) add variable numberOfItems

var numberOfItems: Int {
    get {
        return secrets.count
    }
}

2) change this line self.stories = articles to self.stories += articles

3) add function for pagination:

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {

    if (indexPath.item + 1 == numberOfItems) && ((indexPath.item + 1) % numberOfPagination == 0) {

        if self.presenter.hasMoreItems {
            self.loadData()
        }
    }
}

f) add func loadData()

func loadData() {
    Artikel.getArticles(category["id"].intValue, nextPageUrl: nextPageUrl) {
        (articles, error) in
        self.loadingIndicator.stopAnimating()
        if error == nil {
            self.stories = articles
            self.collectionView.reloadData()
        }
    }
}

In Artikel:

1) change getArticles function

static func getArticles(_ category_id: Int, nextPageUrl: String?, completionHandler: @escaping ArrayCompletionHandler) {

    //...

    let new_api = nextPageUrl ?? Config.server_addforarticle + newcategory

    //...
}

2) in this function you can return nextPageUrl value in ArrayCompletionHandler

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source: stackoverflow.com
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