1. DownloadWithEscaping 下载数据并且转义返回数据

  1.1 实现

struct PostDataModel:Identifiable, Codable {
    let userId: Int
    let id: Int
    let title: String
    let body: String
}

/// ViewModel
class DownloadWithEscapingViewModel: ObservableObject{
    @Published var posts: [PostDataModel] = []
    
    init() {
        getPosts()
    }
    
    // post 请求
    func getPosts(){
        // https://jsonplaceholder.typicode.com/posts
        // https://jsonplaceholder.typicode.com/posts/1
        guard let url = URL(string: "https://jsonplaceholder.typicode.com/posts") else{ return }
        
        downloadData(formURL: url) { returnedData in
            if let data = returnedData{
                // 解码模型
                guard let newPosts = try? JSONDecoder().decode([PostDataModel].self, from: data) else { return }
                
                DispatchQueue.main.async { [weak self] in
                    // 添加到数组中
                    //self?.posts.append(newPost)
                    self?.posts = newPosts
                }
            }else{
                print("No data returned.")
            }
        }
    }
    
    
    /// 封装请求接口 formURL:  外部名称   @escaping: 转义闭包
    func downloadData(formURL url: URL, completionHandler: @escaping (_ data: Data?) -> ()){
        URLSession.shared.dataTask(with: url) { data, response, error in
            // 检查有没有数据
            //guard let data = data else{
            //    print("No data.")
            //    return
            //}
            
            // 检查有没有错误
            //guard error == nil else{
            //    print("Error: \(String(describing: error))")
            //    return
            //}
            
            // 判断返回 httpurl 响应
            //guard let response = response as? HTTPURLResponse else{
            //    print("Invalid response.")
            //    return
            //}
            
            // 判断返回状态码
            //guard response.statusCode >= 200 && response.statusCode < 300 else{
            //    print("Status code should be 2xx, but is \(response.statusCode)")
            //    return
            //}
            
            // 打印接收数据
            //print("Successfully downloaded data!")
            //print(data)
            //let jsonData = String(data: data, encoding: .utf8)
            //print(jsonData ?? "")
            
            guard let data = data,
                  error == nil,
                  let response = response as? HTTPURLResponse,
                  response.statusCode >= 200 && response.statusCode < 300 else{
                print("Error downloading data.")
                completionHandler(nil)
                return
            }
            // 返回数据
            completionHandler(data)
        }.resume()
    }
}

/// 下载并且转义
struct DownloadWithEscapingBootcamp: View {
    @StateObject var vm = DownloadWithEscapingViewModel()
    
    var body: some View {
        List {
            ForEach(vm.posts) { post in
                VStack(alignment: .leading) {
                    Text(post.title)
                        .font(.headline)
                    Text(post.body)
                        .foregroundColor(.gray)
                }
                .frame(maxWidth: .infinity, alignment: .leading)
            }
        }
    }
}

  1.2 效果图:

2. DownloadWithCombine 下载数据并且组合使用数据

  2.1 实现

import Combine

struct PostModel:Identifiable, Codable {
    let userId: Int
    let id: Int
    let title: String
    let body: String
}

// ViewModel
class DownloadWithCombineViewModel: ObservableObject{
    @Published var posts:[PostModel] = []
    // 是否取消请求
    var cancellables = Set<AnyCancellable>()
    
    init() {
        getPosts()
    }
    
    // 获取数据
    func getPosts(){
        guard let url = URL(string: "https://jsonplaceholder.typicode.com/posts") else{ return }
        
        // Combine discussion:
        /*
        // 1. 注册信息，按月订阅一个包裹，订阅后然后发送给公司
        // 2. 公司将制做包裹，因此工厂继续制作他们的包裹
        // 3. 制作完包裹，然后运送包裹，您可能会在门前收到包裹
        // 4. 您将检查箱子，确保箱子没有损坏
        // 5. 打开并确保商品无误
        // 6. 最终可以使用
        // 7. 订阅的包裹，可以随时取消
        
        // 1. 创建发布者
        // 2. 后台线程上订阅发布者
        // 3. 主线程上接收
        // 4. tryMap 检查数据是否完好
        // 5. 解码 (解码数据到模型(PostModel))
        // 6. sink，进行同步，并将 item 放入项目
        // 7. store (随时取消订阅)
         */
        URLSession.shared.dataTaskPublisher(for: url)
            //.subscribe(on: DispatchQueue.global(qos: .background))
            .receive(on: DispatchQueue.main)
            .tryMap(handleOutput)
            .decode(type: [PostModel].self, decoder: JSONDecoder())
             // 不想处理错误信息，简单写法
            .replaceError(with: []) // 替代错误
            .sink(receiveValue: { [weak self]returnedPosts in
                self?.posts = returnedPosts
            })
            /*.sink { completion in
                // 打印信息 -> 包含 URLError
                //print("Completion: \(completion)")
                switch completion {
                case .finished:
                    print("Finished")
                case .failure(let error):
                    print("There was an error: \(error)")
                }
            } receiveValue: {[weak self] returnedPosts in
                self?.posts = returnedPosts
            }*/
            .store(in: &cancellables)
    }
    
    // 抽取函数
    func handleOutput(output: URLSession.DataTaskPublisher.Output) throws -> Data{
        guard let response = output.response as? HTTPURLResponse,
              response.statusCode >= 200 && response.statusCode < 300 else{
            throw URLError(.badServerResponse)
        }
        return output.data
    }
}

// 组合操作
struct DownloadWithCombine: View {
    @StateObject var viewModel = DownloadWithCombineViewModel()
    
    var body: some View {
        List {
            ForEach(viewModel.posts) { post in
                VStack(alignment: .leading) {
                    Text(post.title)
                        .font(.headline)
                    Text(post.body)
                        .foregroundColor(.gray)
                }
                .frame(maxWidth: .infinity, alignment: .leading)
            }
        }
    }
}

  2.2 效果图: