timstudt · January 17, 2019 09:11 · Jan 17, 2019
diff --git a/ViewStates.playground b/ViewStates.playground
@@ -0,0 +1,140 @@
+//: A UIKit based Playground for presenting user interface
+
+import UIKit
+import PlaygroundSupport
+
+// Models
+
+struct MyViewModel: Equatable { let text: String }
+
+enum MyError: Error, Equatable {
+    case noConnection(String)
+}
+
+// Protocols
+
+protocol ViewState: Equatable {
+    associatedtype T: Equatable
+    associatedtype Error: Equatable
+    var isLoading: Bool { get }
+    var data: T? { get }
+    var error: Error? { get }
+}
+
+protocol Presenting {
+    func loadData()
+}
+
+protocol UI: class {
+    associatedtype State
+    func render(state: State)
+}
+
+// Base Classes
+class Presenter<V: UI> {
+    weak var ui: V?
+}
+
+// Module Classes
+
+final class MyPresenter: Presenter<MyView>, Presenting {
+    func loadData() {
+        ui?.render(state: .loading)
+        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
+            self.ui?.render(state: .error(.noConnection("oops, we messed up!")))
+        }
+        DispatchQueue.main.asyncAfter(deadline: .now() + 4) {
+            self.ui?.render(state: .loaded(.init(text: "kidding..got some data")))
+        }
+    }
+}
+
+class MyView : UIViewController {
+    let presenter: MyPresenter
+    var lable: UILabel!
+
+    init(presenter: MyPresenter = MyPresenter()) {
+        self.presenter = presenter
+        super.init(nibName: nil, bundle: nil)
+        presenter.ui = self
+    }
+
+    required init?(coder aDecoder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    override func loadView() {
+        let view = UIView()
+        view.backgroundColor = .white
+
+        let label = UILabel()
+        label.frame = CGRect(x: 150, y: 200, width: 250, height: 20)
+        label.text = "Hello World!"
+        label.textColor = .black
+
+        view.addSubview(label)
+        self.lable = label
+        self.view = view
+    }
+
+    override func viewDidAppear(_ animated: Bool) {
+        super.viewDidAppear(animated)
+        presenter.loadData()
+    }
+
+    private func showSpinner() {
+        lable.textColor = .gray
+        lable.text = "..loading"
+    }
+
+    private func show(data: MyViewModel) {
+        lable.textColor = .black
+        lable.text = data.text
+    }
+
+    private func show(error: MyError) {
+        lable.textColor = .red
+        switch error {
+        case .noConnection(let mesg):
+            lable.text = mesg
+        }
+    }
+}
+
+extension MyView: UI {
+    typealias T = State
+    func render(state: State) {
+        switch state {
+        case .loading: showSpinner()
+        case .loaded(let data): show(data: data)
+        case .error(let error): show(error: error)
+        }
+    }
+}
+
+extension MyView {
+    enum State {
+        typealias T = MyViewModel
+        typealias Error = MyError
+        case loading, loaded(T), error(Error)
+    }
+}
+
+extension MyView.State: ViewState {
+    var isLoading: Bool { return self == .loading }
+    var data: MyViewModel? {
+        switch self {
+        case .loading, .error: return nil
+        case .loaded(let data): return data
+        }
+    }
+    var error: MyError? {
+        switch self {
+        case .loading, .loaded: return nil
+        case .error(let mesg): return mesg
+        }
+    }
+}
+
+// Present the view controller in the Live View window
+PlaygroundPage.current.liveView = MyView()