SwiftUI:在 ViewModel 中预览数据

Question

我从一个从 web 加载数据的 viewModel 加载我的数据。问题:我想设置一些预览示例数据以在预览窗口中包含内容。目前我的预览包含一个空列表，因为我不提供数据。

我怎样才能做到这一点？

struct MovieListView: View {

    @ObservedObject var viewModel = MovieViewModel()

    var body: some View {
       List{
        ForEach(viewModel.movies) { movie in
                MovieRow(movie: movie)
                    .listRowInsets(EdgeInsets())
            }
        }
    }
}

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

class MovieViewModel: ObservableObject{

    private let provider = NetworkManager()

    @Published var movies = [Movie]()

    init() {
       loadNewMovies()
    }

    func loadNewMovies(){
         provider.getNewMovies(page: 1) {[weak self] movies in
                   print("\(movies.count) new movies loaded")
                   self?.movies.removeAll()
            self?.movies.append(contentsOf: movies)}
    }
}

Answer 1

这是可能的方法(基于 View 模型成员的依赖注入(inject)而不是紧耦合)

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        // create Movie to be previewed inline, say from bundled data
        MovieListView(viewModel: MovieViewModel(provider: nil, movies: [Movie(...)]))
    }
}

class MovieViewModel: ObservableObject {

    private var provider: NetworkManager?

    @Published var movies: [Movie]

    // same as before by default, but allows to modify if/when needed explicitly
    init(provider: NetworkManager? = NetworkManager(), movies: [Movie] = []) {
        self.provider = provider
        self.movies = movies

        loadNewMovies()
    }

    func loadNewMovies(){
         provider?.getNewMovies(page: 1) {[weak self] movies in
                print("\(movies.count) new movies loaded")
                self?.movies.removeAll()
                self?.movies.append(contentsOf: movies)
        }
    }
}