<div id="readability-page-1" class="page"><div>Swift State Enum 을 이용하여 tableview의 empty, pagination, error view를 처리하는 방법<ul><li><a href="https://www.raywenderlich.com/5542-enum-driven-tableview-development">Link</a></li><li>위의 글을 참조하여 itunes search list에 적용한다.</li><li>original source</li></ul><pre data-lang="swift"><code data-lang="swift">class ListController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

 fileprivate let cellId = "cellId"
 fileprivate let footerId = "footerId"

 override func viewDidLoad() {
 super.viewDidLoad()
 collectionView.backgroundColor = .white

 collectionView.register(ListCell.self, forCellWithReuseIdentifier: cellId)
 collectionView.register(LoadingFooter.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionFooter, withReuseIdentifier: footerId)

 fetchData()
 }

 var results = [Result]()

 fileprivate let searchTerm = "BTS"

 fileprivate func fetchData() {
 let urlString = "https://itunes.apple.com/search?term=\(searchTerm)&amp;offset=0&amp;limit=20"
 Service.shared.fetchGenericJSONData(urlString: urlString) { (searchResult: SearchResult?, err) in

 if let err = err {
 print("Failed to paginate data:", err)
 return
 }

 self.results = searchResult?.results ?? []
 DispatchQueue.main.async {
 self.collectionView.reloadData()
 }
 }
 }

 override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -&gt; UICollectionReusableView {
 let footer = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: footerId, for: indexPath)
 return footer
 }

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForFooterInSection section: Int) -&gt; CGSize {
 let height: CGFloat = isDonePaginating ? 0 : 100
 return .init(width: view.frame.width, height: height)
 }

 override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -&gt; Int {
 return results.count
 }

 var isPaginating = false
 var isDonePaginating = false

 override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -&gt; UICollectionViewCell {
 let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! ListCell

 let track = results[indexPath.item]
 cell.configure(viewData: track)
 // initiate pagination
 if indexPath.item == results.count - 1 &amp;&amp; !isPaginating {
 print("fetch more data")

 isPaginating = true

 let urlString = "https://itunes.apple.com/search?term=\(searchTerm)&amp;offset=\(results.count)&amp;limit=20"
 Service.shared.fetchGenericJSONData(urlString: urlString) { (searchResult: SearchResult?, err) in

 if let err = err {
 print("Failed to paginate data:", err)
 return
 }

 if searchResult?.results.count == 0 {
 self.isDonePaginating = true
 }

 sleep(2)

 self.results += searchResult?.results ?? []
 DispatchQueue.main.async {
 self.collectionView.reloadData()
 }
 self.isPaginating = false
 }
 }

 return cell
 }

 func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -&gt; CGSize {
 return .init(width: view.frame.width, height: 100)
 }

}

</code></pre><h2 id="different-states">Different States</h2><ul><li>잘 디자인된 리스트는 다음의 4가지 state를 가진다 <ul><li>Loading: The app is busy fetching new data.</li><li>Error: A service call or another operation has failed.</li><li>Empty: The service call has returned no data.</li><li>Populated: The app has retrieved data to display.</li></ul></li></ul><h2 id="state-enumeul-iyonghayeo-refactoring">state enum을 이용하여 refactoring</h2><ul><li>enum 추가</li></ul><pre data-lang="swift"><code data-lang="swift"> case loading
 case paging([Result])
 case populated([Result])
 case empty
 case error(Error)

 var currentResults: [Result] {
 switch self {
 case .paging(let results):
 return results
 case .populated(let results):
 return results
 default:
 return []
 }
 }

</code></pre><ul><li>property observer를 적용한 state variable 추가</li><li>다른곳에 사용한 collectionView.reloadData() 는 모두 지운다.</li></ul><pre data-lang="swift"><code data-lang="swift"> var state = State.loading {
 didSet {
 DispatchQueue.main.async {
 self.collectionView.reloadData()
 }
 }
 }

</code></pre><ul><li><code>results</code> 전역 변수를 지우고 <code>state.currentResults</code> 로 변경한다.</li><li><code>isPaginating</code>, <code>isDonePaginating</code> 전역변수도 지우고 state 변경으로 refactoring</li></ul><pre data-lang="swift"><code data-lang="swift"> fileprivate func loadPage() {
 state = .paging(state.currentResults)
 let urlString = "https://itunes.apple.com/search?term=\(searchTerm)&amp;offset=\(state.currentResults.count)&amp;limit=20"
 Service.shared.fetchGenericJSONData(urlString: urlString) { (searchResult: SearchResult?, err) in
 if let err = err {
 self.state = .error(err)
 return
 }

 if searchResult?.results.count == 0 {
 self.state = .empty
 return
 }

 sleep(2)

 var allResults = self.state.currentResults
 allResults += searchResult?.results ?? []
 self.state = .populated(allResults)
 }
 }
</code></pre><h2 id="final-source">final source</h2><ul><li><a href="https://github.com/wonkwh/BlogShowcase/blob/develop/BlogShowcase/BlogShowcase/showcase/EnumListController.swift">here</a></li></ul><h2 id="next">next</h2><ul><li>swift composale architecture 를 이용하여 변경</li></ul></div></div>

kwanghyun won

Swift State Enum 을 이용하여 tableview의 empty, pagination, error view를 처리하는 방법

Enum-Driven TableView Development

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