在 SwiftUI 中，视图不会随着模型更新而更新

如何解决在 SwiftUI 中，视图不会随着模型更新而更新

在项目中，我调用了 Google 的 eBook API 来列出图书。它默认列出哈利波特书籍。除此之外，我有一个搜索栏来搜索其他主题的书，比如“java”。它工作正常，当我开始在搜索字段中写入时，我的视图模型会更新模型中的书籍数组。但是，它根本没有更新我的观点。我已提供以下所有代码。

型号：

import Foundation

struct BookModel {
    var books: [Book] = []
    
    struct Book: Identifiable {
        var id: String
        var title: String
        var authors: String
        var desc: String
        var imurl: String
        var url: String
    }
}

视图模型：

import Foundation
import SwiftyJSON

class BookViewModel: ObservableObject {
    @Published var model = BookModel()
    
    init(searchText: String) {
        let url = "https://www.googleapis.com/books/v1/volumes?q=\(searchText)"
        print(url)
        
        let session = URLSession(configuration: .default)
        session.dataTask(with: URL(string: url)!) { (resp,_,error) in
            if error != nil {
                print(error?.localizedDescription ?? "Error")
                return
            }
            let json = try! JSON(data: resp!)
            let items = json["items"].array!
            
            for item in items {
                let id = item["id"].stringValue
                let title = item["volumeInfo"]["title"].stringValue
                let authors = item["volumeInfo"]["authors"].array ?? []
                var author: String = ""
                for name in authors {
                    author += "\(name.stringValue)"
                }
                let description = item["volumeInfo"]["description"].stringValue
                let imurl = item["volumeInfo"]["imageLinks"]["thumbnail"].stringValue
                let webReaderLink = item["volumeInfo"]["previewLink"].stringValue
                print(title)
                DispatchQueue.main.async {
                    self.model.books.append(BookModel.Book(id: id,title: title,authors: author,desc: description,imurl: imurl,url: webReaderLink))
                }
            }
        }
        .resume()
        
        // For testing
        for i in model.books {
            print(i.title)
        }
    }
    
    //MARK:- Access to the model
    
    var books: [BookModel.Book] {
        model.books
    }
}

内容视图：

import SwiftUI

struct ContentView: View {
    @ObservedObject var viewModel = BookViewModel(searchText: "harry+potter")

    var body: some View {
        CustomNavigationView(view: AnyView(Home(viewModel: viewModel)),placeHolder: "Search",largeTitle: true,title: "Books") { (text) in
            if text != "" {
                BookViewModel(searchText: text.lowercased().replacingOccurrences(of: " ",with: "+"))
            }
        } onCancel: {
            BookViewModel(searchText: "harry+potter")
        }
        .edgesIgnoringSafeArea(.all)
    }
}

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

主页：

import SwiftUI
import SDWebImageSwiftUI

struct Home: View {
    @ObservedObject var viewModel: BookViewModel
    @State private var show: Bool = false
    @State var previewURL = ""
    
    var body: some View {
        List {
            ForEach(viewModel.books) { book in
                HStack {
                    if book.imurl != "" {
                        WebImage(url: URL(string: book.imurl))
                            .resizable()
                            .frame(width: 120,height: 170)
                    } else {
                        Image(systemName: "character.book.closed.fill")
                            .font(.system(size: 60))
                            .frame(width: 120,height: 170)
                    }
                    VStack(alignment: .leading,spacing: 10) {
                        Text(book.title)
                            .fontWeight(.bold)
                        Text(book.authors)
                        Text(book.desc)
                            .font(.system(size: 13))
                            .lineLimit(4)
                            .multilineTextAlignment(.leading)
                    }
                }
                .onTapGesture {
                    self.previewURL = book.url
                    show.toggle()
                }
            }
        }
        .sheet(isPresented: $show) {
            NavigationView {
                WebView(url: $previewURL)
                    .navigationBarTitle("Book Preview")
            }
        }
    }
}

自定义导航视图：

import SwiftUI

struct CustomNavigationView: UIViewControllerRepresentable {
    func makeCoordinator() -> Coordinator {
        return CustomNavigationView.Coordinator(parent: self)
    }
    
    var view: AnyView
    
    //onSearch and onCancel Closures
    var onSearch: (String) -> ()
    var onCancel: () -> ()
    
    var title: String
    var largeTitle: Bool
    var placeHolder: String
    
    init(view: AnyView,placeHolder: String? = "Search",largeTitle: Bool? = false,title: String,onSearch: @escaping (String) -> (),onCancel: @escaping () -> ()) {
        self.title = title
        self.largeTitle = largeTitle!
        self.placeHolder = placeHolder!
        self.view = view
        self.onSearch = onSearch
        self.onCancel = onCancel
    }
    
    func makeUIViewController(context: Context) -> UINavigationController {
        let childView = UIHostingController(rootView: view)
        let controller = UINavigationController(rootViewController: childView)
        
        controller.navigationBar.topItem?.title = title
        controller.navigationBar.prefersLargeTitles = largeTitle
        
        let searchController = UISearchController()
        searchController.searchBar.placeholder = placeHolder
        searchController.obscuresBackgroundDuringPresentation = false
        searchController.searchBar.delegate = context.coordinator
        
        controller.navigationBar.topItem?.hidesSearchBarWhenScrolling = false
        controller.navigationBar.topItem?.searchController = searchController
        
        return controller
    }
    func updateUIViewController(_ uiViewController: UINavigationController,context: Context) {
        uiViewController.navigationBar.topItem?.title = title
        uiViewController.navigationBar.topItem?.searchController?.searchBar.placeholder = placeHolder
        uiViewController.navigationBar.prefersLargeTitles = largeTitle
    }
    
    //Search Bar Delegate
    class Coordinator: NSObject,UISearchBarDelegate {
        var parent: CustomNavigationView
        
        init(parent: CustomNavigationView) {
            self.parent = parent
        }
        
        func searchBar(_ searchBar: UISearchBar,textDidChange searchText: String) {
            self.parent.onSearch(searchText)
        }
        func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
            self.parent.onCancel()
        }
    }
}

完整项目链接： https://github.com/shawkathSrijon/eBook-Reader.git

解决方法

您可能需要使用 ObservableObjectPublisher objectWillChange 来表达您对新更改的看法。

DispatchQueue.main.async {
    self.model.books.append(BookModel.Book(id: id,title: title,authors: author,desc: description,imurl: imurl,url: webReaderLink))
    self.objectWillChange.send() // <-- Here
}