合并SwiftUI远程获取数据-ObjectBinding不会更新视图

Posted 2021-04-13

我正在尝试学习Combine，这对我来说是PITA。我没学过RX Swift，所以这是全新的。我敢肯定，我缺少这种简单的东西，但希望能有所帮助。

我正在尝试从API提取一些JSON并加载到列表视图中。我有一个符合ObservableObject的视图模型，并更新了一个@Published属性，该属性是一个数组。我使用该VM来加载列表，但是看起来该API返回之前，视图的加载方式（列表显示为空白）。我希望这些属性包装器能够执行我认为应该做的事情，并在对象更改时重新渲染视图。

就像我说的那样，我确定我缺少简单的东西。如果您能找到它，我将很乐意为您提供帮助。谢谢

class PhotosViewModel: ObservableObject {

    var cancellable: AnyCancellable?

    @Published var photos = Photos()

    func load(user collection: String) {
        guard let url = URL(string: "https://api.unsplash.com/users/(collection)/collections?client_id=(Keys.unsplashAPIKey)") else {
            return
        }
        cancellable = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: Photos.self, decoder: JSONDecoder())
            .replaceError(with: defaultPhotosObject)
            .receive(on: RunLoop.main)
            .assign(to: .photos, on: self)
    }

}

struct PhotoListView: View {
    @EnvironmentObject var photosViewModel: PhotosViewModel
    var body: some View {
        NavigationView {
            List(photosViewModel.photos) { photo in
                NavigationLink(destination: PhotoDetailView(photo)) {
                    PhotoRow(photo)
                }
            }.navigationBarTitle("Photos")
        }
    }
}

struct PhotoRow: View {
    var photo: Photo
    init(_ photo: Photo) {
        self.photo = photo
    }
    var body: some View {
        HStack {
            ThumbnailImageLoadingView(photo.coverPhoto.urls.thumb)
            VStack(alignment: .leading) {
                Text(photo.title)
                    .font(.headline)
                Text(photo.user.firstName)
                    .font(.body)
            }
            .padding(.leading, 5)
        }
        .padding(5)
    }
}

答案

这最终导致我的Codable结构设置不正确。一旦在。replaceError方法中添加了默认对象而不是空白数组（感谢@Asperi），便能够看到解码错误并进行修复。现在就像魅力一样！

原件：

    func load(user collection: String) {
        guard let url = URL(string: "https://api.unsplash.com/users/(collection)/collections?client_id=(Keys.unsplashAPIKey)") else {
            return
        }
        cancellable = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: Photos.self, decoder: JSONDecoder())
            .replaceError(with: [])
            .receive(on: RunLoop.main)
            .assign(to: .photos, on: self)
    }

更新：

    func load(user collection: String) {
        guard let url = URL(string: "https://api.unsplash.com/users/(collection)/collections?client_id=(Keys.unsplashAPIKey)") else {
            return
        }
        cancellable = URLSession.shared.dataTaskPublisher(for: url)
            .map { $0.data }
            .decode(type: Photos.self, decoder: JSONDecoder())
            .replaceError(with: defaultPhotosObject)
            .receive(on: RunLoop.main)
            .assign(to: .photos, on: self)
    }