如何在 SwiftUI 中声明 viewModel 对象? [英] How should the viewModel object be declared in SwiftUI?

问题描述

我正在尝试使用在我的视图结构中声明为 @ObservedObject 的 @ObservableObject viewModel.问题是当 viewModel 改变它的域"时.属性@Published var，UI 未更新.另外，我更改了在 init() {} 中调用的 getDomains() 函数内的域.看起来它被调用了两次，为什么会发生这种情况?这是我的 viewModel 代码:

I am trying to use an @ObservableObject viewModel which is declared as @ObservedObject inside my view struct. The problem is that when the viewModel changes it's "domains" property @Published var, the UI is not updating. Also, I change domains inside getDomains() function which is called inside init() {}. Looks like it is called twice, why is that happening? Here's my code for viewModel:

import Combine

class DomainsViewModel: ObservableObject {

    @Published var domains: [InterestDomain] = [InterestDomain]()
    
    init() {
        self.getDomains { (response) in
            print(response)
        }
    }
    
    func getDomains(completion: @escaping (Bool) -> Void) {
        NetworkEngine.shared.appNetwork.getInterestDomains { result in
            self.domains.removeAll()
            switch result {
            case .success(let domainsOfInterest):
                if let domainsList = domainsOfInterest {
                    self.domains = domainsList
                }
                completion(true)
            case .failure(_):
                completion(false)
            }
        }
    }

}

视图代码:进口基金会导入 SwiftUI导入组合

Code for the view: import Foundation import SwiftUI import Combine

struct DomainsOfInterestView: View {

    @ObservedObject var viewModel: DomainsViewModel = DomainsViewModel()
    
    @State var isActive = true
    
    var body: some View {
            VStack(alignment: .center) {
                HStack {
                    Text("Choose domains of interest for your profile")
                        .font(.headline)
                    Spacer()
                }.padding(.bottom, 16)
                
                ForEach(viewModel.domains.indices) { index in
                    DomainOfInterestElement(isActive: self.$isActive, domain: self.viewModel.domains[index].name)
                }

                OrangeButton(action: {
                }) {
                    Text("Save")
                }.padding(.top, 30)
                    .padding([.leading, .trailing], 30)
                Spacer()
            }.padding([.leading, .trailing], 12)
            .navigationBarTitle("Domains of interest")
    }
}

struct DomainsOfInterestView_Previews: PreviewProvider {
    static var previews: some View {
    DomainsOfInterestView()
    }
}

struct DomainOfInterestElement: View {
    @Binding var isActive: Bool
    var domain: String
    var body: some View {
        Button(action: {
            self.isActive.toggle()
        }) {
            VStack {
                Divider().padding(.bottom, 12)
                HStack {
                    checkBoxView()
                        .frame(width: 36, height: 36)
                    textView().font(.custom("SFProDisplay-Regular", size: 16))
                    Spacer()
                }
            }
        }
    }
    
    func checkBoxView() -> Image {
        switch isActive {
        case true:
            return Image(uiImage: #imageLiteral(resourceName: "check-box-active-2-1")).renderingMode(.original)
        case false:
            return Image(uiImage: #imageLiteral(resourceName: "check-box-active-1")).renderingMode(.original)
        }
    }
    func textView() -> Text {
        switch isActive {
        case true:
            return Text(domain)
                .foregroundColor(.black)
        case false:
            return Text(domain)
                .foregroundColor(Color.orGrayColor)
        }
    }
}

有人可以帮我吗?谢谢.

Could anyone help me please? Thanks.

推荐答案

DomainsOfInterestView 在其视图模型的每次更新时重新创建.并且每次都使用新的 DomainsViewModel 实例初始化视图模型属性.一个新的视图模型会将 domains 属性设置为 [InterestDomain]() 并且 self.getDomains 将被再次调用.

DomainsOfInterestView is recreated on every update of its view model. And you initialise the view model property with a new DomainsViewModel instance every time. A new view model will have the domains property set to [InterestDomain]() and self.getDomains will be called again.

首先，最好将 viewModel 注入到初始化器中的 DomainsOfInterestView，正如@youjin 在上一篇文章的评论中所写的那样.此外，如果您的最低部署目标允许，您可以使用 @StateObject 而不是 @ObservedObject.在这种情况下，每次更新视图时都不会重置 viewModel 属性.

First of all, better to inject the viewModel to DomainsOfInterestView in an initiailiser as @youjin wrote in a comment to the previous post. Also, you can use @StateObject instead of @ObservedObject if your minimum deployment target allows that. In this case, the viewModel property won't be reset every time the view is updated.

这篇关于如何在 SwiftUI 中声明 viewModel 对象?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！