IGListKit/Example/IGListKitExamples/ViewControllers/LoadMoreViewController.swift

/**
 Copyright (c) 2016-present, Facebook, Inc. All rights reserved.

 The examples provided by Facebook are for non-commercial testing and evaluation
 purposes only. Facebook reserves all rights not expressly granted.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

import UIKit
import IGListKit

class LoadMoreViewController: UIViewController, IGListAdapterDataSource, UIScrollViewDelegate {

    lazy var adapter: IGListAdapter = {
        return IGListAdapter(updater: IGListAdapterUpdater(), viewController: self, workingRangeSize: 0)
    }()
    let collectionView = IGListCollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())

    lazy var items = Array(0...20)
    var loading = false
    let spinToken = NSObject()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(collectionView)
        adapter.collectionView = collectionView
        adapter.dataSource = self
        adapter.scrollViewDelegate = self
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        collectionView.frame = view.bounds
    }

    //MARK: IGListAdapterDataSource

    func objects(for listAdapter: IGListAdapter) -> [IGListDiffable] {
        var objects = items as [IGListDiffable]
        
        if loading {
            objects.append(spinToken)
        }
        
        return objects
    }

    func listAdapter(_ listAdapter: IGListAdapter, sectionControllerFor object: Any) -> IGListSectionController {
        if let obj = object as? NSObject, obj === spinToken {
            return spinnerSectionController()
        } else {
            return LabelSectionController()
        }
    }

    func emptyView(for listAdapter: IGListAdapter) -> UIView? { return nil }

    //MARK: UIScrollViewDelegate

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let distance = scrollView.contentSize.height - (targetContentOffset.pointee.y + scrollView.bounds.height)
        if !loading && distance < 200 {
            loading = true
            adapter.performUpdates(animated: true, completion: nil)
            DispatchQueue.global(qos: .default).async(execute: {
                // fake background loading task
                sleep(2)
                DispatchQueue.main.async {
                    self.loading = false
                    let itemCount = self.items.count
                    self.items.append(contentsOf: Array(itemCount..<itemCount + 5))
                    self.adapter.performUpdates(animated: true, completion: nil)
                }
            })
        }
    }

}