dismiss_guardian.swift

//
//  ContentView.swift
//  DissmissGesture
//
//  Created by MC on 2020/5/29.
//  Copyright © 2020 MC. All rights reserved.
//

import SwiftUI
import UIKit

struct ContentView: View {
    @State private var show = false
    @ObservedObject var dataModel = MyDataModel()
    
    var body: some View {
        DissmissGuardian(preventDismiss: $dataModel.preventDissmissal, attempted: $dataModel.attempted) {
            VStack {
                Spacer()
                
                Text("演示如何监听Dissmiss手势").font(.title)
                
                Spacer()
                
                Button("跳转到新的View") {
                    self.show = true
                }
                .sheet(isPresented: self.$show) {
                    MyCustomerView().environmentObject(self.dataModel)
                }
                
                Spacer()
            }
        }
    }
}

class MyDataModel: ObservableObject {
    @Published var attempted = false
    @Published var preventDissmissal = false
    
    @Published var firstName: String = "" {
        didSet {
            updatePrecentDissmissal()
        }
    }
    
    @Published var lastName: String = "" {
        didSet {
            updatePrecentDissmissal()
        }
    }
    
    func updatePrecentDissmissal() {
        self.preventDissmissal = (self.firstName != "" || self.lastName != "")
    }
    
    func save() {
        self.reset()
    }
    
    func reset() {
        self.firstName = ""
        self.lastName = ""
    }
}

protocol DismissGuardianDelegate {
    func attemptedUpdate(flag: Bool)
}

class DismissGuardianUIHostingController<Content>: UIHostingController<Content>, UIAdaptivePresentationControllerDelegate where Content: View {
    var preventDismissal: Bool
    var dismissGuardianDelegate: DismissGuardianDelegate?
    
    init(rootView: Content, preventDismissal: Bool) {
        self.preventDismissal = preventDismissal
        super.init(rootView: rootView)
    }
    
    @objc required dynamic init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func present(_ viewControllerToPresent: UIViewController, animated flag: Bool, completion: (() -> Void)? = nil) {
        viewControllerToPresent.presentationController?.delegate = self
        dismissGuardianDelegate?.attemptedUpdate(flag: false)
        super.present(viewControllerToPresent, animated: flag, completion: completion)
    }
    
    func presentationControllerDidAttemptToDismiss(_ presentationController: UIPresentationController) {
        dismissGuardianDelegate?.attemptedUpdate(flag: true)
    }
    
    func presentationControllerShouldDismiss(_ presentationController: UIPresentationController) -> Bool {
        return !self.preventDismissal
    }
}

struct DissmissGuardian<Content: View>: UIViewControllerRepresentable {
    @Binding var preventDismiss: Bool
    @Binding var attempted: Bool
    var content: Content
    
    init(preventDismiss: Binding<Bool>, attempted: Binding<Bool>, @ViewBuilder content: @escaping () -> Content) {
        self._preventDismiss = preventDismiss
        self._attempted = attempted
        self.content = content()
    }
    
    func makeUIViewController(context: Context) -> UIViewController {
        return DismissGuardianUIHostingController(rootView: self.content, preventDismissal: self.preventDismiss)
    }
    
    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {
        let dismissHosting = uiViewController as! DismissGuardianUIHostingController<Content>
        dismissHosting.preventDismissal = self.preventDismiss
        dismissHosting.rootView = self.content
        dismissHosting.dismissGuardianDelegate = context.coordinator
    }
    
    func makeCoordinator() -> Coordinator {
        return Coordinator(attempted: $attempted)
    }
    
    class Coordinator: NSObject, DismissGuardianDelegate {
        @Binding var attempted: Bool
        
        init(attempted: Binding<Bool>) {
            self._attempted = attempted
        }
        
        func attemptedUpdate(flag: Bool) {
            self.attempted = flag
        }
    }
}

struct MyCustomerView: View {
    @EnvironmentObject var dataModel: MyDataModel
    @Environment(\.presentationMode) private var presentationMode
    
    var body: some View {
        NavigationView {
            Form {
                TextField("姓", text: $dataModel.firstName)
                TextField("名", text: $dataModel.lastName)
            }
            .navigationBarTitle("编辑姓名")
            .navigationBarItems(trailing:
                Button("保存") {
                    self.dataModel.save()
                    self.presentationMode.wrappedValue.dismiss()
                }
            )
            .alert(isPresented: $dataModel.attempted) {
                Alert(title: Text("警告"), message: Text("请填写姓名"), primaryButton: .default(Text("仍然退出")), secondaryButton: .cancel())
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}