MVVM 模式服务调用响应未出现在 swift 的 Viewcontroller 中

MVVM pattern service call response not coming in Viewcontroller in swift

提问人:Swift 提问时间:11/16/2023 更新时间:11/16/2023 访问量:41

问:

我正在使用MVVM模式进行服务调用

代码:在ViewController中,调用和响应也来了,但为什么为零?postGenericCallVMprint("testing viewmodel data in viewcontroller \(String(describing: postVM.postDataVM?.postCount))")

我哪里错了?

struct RequestObject {
var params: [String: Any]? = nil
var method: HTTPMethod
var urlPath: String
var isTokenNeeded: Bool
var isLoaderNeed: Bool = false
var isErrorNeed: Bool = false
var vc: UIViewController?
}

class APINetworkManager2: NSObject {
static let sharedInstance = APINetworkManager2()

fileprivate override init() {
    super.init()
}

func serviceCall<T: Decodable>(requestObject: RequestObject, completion: @escaping (Result<APIResponse<T>, Error>) -> Void) {
    
    guard let url = URL(string: requestObject.urlPath) else {
        return
    }
    
    var urlRequest = URLRequest(url: url)
    
    if requestObject.isTokenNeeded {
        let token = "Bearer token" // Replace with your actual token
        urlRequest.setValue(token, forHTTPHeaderField: "Authorization")
    }
    
    urlRequest.httpMethod = requestObject.method.rawValue
    
    if let params = requestObject.params {
        let paramsReq: [String: Any] = ["jsonrpc": "2.0", "params": params]
        do {
            urlRequest.httpBody = try JSONSerialization.data(withJSONObject: paramsReq)
        } catch {
            completion(.failure(error))
            return
        }
    }
    
    let task = URLSession.shared.dataTask(with: urlRequest) { data, _, error in
        
        if let data, let string = String(data: data, encoding: .utf8) {
            print("debug check \(string)")
        }
        do {
            
            let response = try JSONDecoder().decode(APIResponse<T>.self, from: data!)
            
            DispatchQueue.main.async {
                completion(.success(response))
            }
        } catch {
            DispatchQueue.main.async {
                completion(.failure(error))
            }
        }
    }
    task.resume()
}
}

这是我的 VIewmodel 代码,在这里打印 o/p 结果视图模型:模型数据即将到来

class PostViewModel {

var postDataVM: PostGenResult?

func postGenericCallVM(){
    
    let param = ["page_no" : "1"] as? [String:Any]
    
    let requestObject = RequestObject(
        params: param,
        method: .post,
        urlPath: "https://hsfjkhskdn",
        isTokenNeeded: true,
        isLoaderNeed: true,
        isErrorNeed: true
    )
    APINetworkManager2.sharedInstance.serviceCall(requestObject: requestObject) { (result: Result<APIResponse<PostGenResult>, Error>) in
        switch result {
        case .success(let response):
            self.postDataVM = response.result as? PostGenResult
            print("result view model: \(self.postDataVM)")
            
        case .failure(let error):
            print("Error decoding JSON: \(error)")
        }
    }
}
}

O/P:在ViewController中成功获取响应

结果视图模型:可选(PracticeCode.PostGenResult(pageCount: 1, perPage: 10, postCount: 5, userReminder: [PracticeCode.UserReminder(id: 17, receiverID: 7, type: “Subscription”, message: “Your Subscription is due in 2

这是我的ViewController代码: 这里

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    
    postVM.postGenericCallVM()
    
    print("testing viewmodel data in viewcontroller \(postVM.postDataVM?.postCount)")
    
}
}

服务呼叫正在呼叫和响应即将到来,但给出零testing viewmodel data in viewcontroller

在 ViewController 中测试 ViewModel 数据:NIL

JSON Swift Web 服务 MVVM

评论

1赞 Teja Nandamuri 11/16/2023
postVM.postGenericCallVM()是异步调用,之后的 print 语句会立即执行,因此在 print 语句中它将是 nil。您可以转换为支持 async/await,或者使用基于闭包的回调,甚至使用基于 combine 的订阅者/发布者来了解 API 调用何时完成,以便随后可以执行 print 语句。postGenericCallVM()

答:

1赞 son 11/16/2023 #1

这是真的,因为您正在请求一个任务,并且需要一些时间进行回调。asyncpostVM.postGenericCallVM()

//Will execute on background thread
APINetworkManager2.sharedInstance.serviceCall

另一方面,这些代码将同步执行。有关更多详细信息,您可以在此处放置日志。

print("Requesting")
postVM.postGenericCallVM()
print("testing viewmodel data in viewcontroller \(postVM.postDataVM?.postCount)")

然后你会看到打印顺序应该是:

Requesting

testing viewmodel data in viewcontroller \(postVM.postDataVM?.postCount)

result view model: \(self.postDataVM)

如何处理?方法1,在函数中添加@escaping补全。postGenericCallVM

func postGenericCallVM(completion: @escaping (() -> Void)) {
    ...
    switch result {
        ...
    }
    completion()
}

postVM.postGenericCallVM { [weak self] in
    //TODO: Re-check postVM.postDataVM here
}

方法二、使用async await

func postGenericCallVM() async {
    await withCheckedContinuation { continuetion in
    ...
        APINetworkManager2.sharedInstance.serviceCall {
            ...
            continuetion.resume(returning: ())
        }
    }
}

Task {
    await postVM.postGenericCallVM()
    print("\(postVM.postDataVM)")
}