如何从 ViewModel 对象填充选择器，设置为第一个元素的初始状态并处理选择选择器项的操作

Posted 2023-02-24

【中文标题】如何从 ViewModel 对象填充选择器，设置为第一个元素的初始状态并处理选择选择器项的操作

【英文标题】：how to populate picker from ViewModel object, setting to initial state of first element and handle actions on selection of picker item

【发布时间】：2020-03-14 09:43:18

【问题描述】：

我有一个视图类，在选择器中显示来自 ViewModel 类的项目列表。此选择器的初始状态是 viewModel 类的对象数组中的第一个元素。

从选择器中选择项目时，我想在该视图中执行不同的操作 - 1. 单击按钮将对象信息发送到不同的屏幕。 2. 显示选择器中选定对象的相关信息。

import SwiftUI
import Combine
struct SetConfiguration: View 


@ObservedObject var profileListVM : ProfilesListViewModel = ProfilesListViewModel()  
@State private var selectedConfiguration  = 0 ///show "Add" as initial state
var body: some View 
HStack 
        Text("Configuration:")

        Picker(selection: $selectedConfiguration.onChange(connectToConfiguration), label: EmptyView()) 
            ForEach(profileListVM.profiles, id: \.self) 
                          choice in
                Text(choice.name).tag(choice)
            
        

        Text (“Selcted item is: \(self. selectedconfiguration.name)”)

        Button(action: 

        ) 
            Text("Edit")
        .sheet(isPresented: $showEditConfig) 
            EditConfigurationView()
                                         //  TODO pass  selectedConfiguration as profile object
        

        

viewModel 类：

class ProfilesListViewModel: ObservableObject  
 @Published var profiles: [ProfileViewModel] = [ProfileViewModel]()   
static var addNewProfile = ProfileViewModel(name: "Add Configuration")
init() 
    fetchAllProfiles()

func fetchAllProfiles() 
     profiles.append(ProfilesListViewModel.addNewProfile) ///Add is first object
    self.profiles = CoreDataManager.shared.getConfigurations().map(ProfileViewModel.init) /// fetch all profile objects    

【问题讨论】：

你编译过这段代码吗？我几乎可以肯定答案是否定的......

【参考方案1】：

我相信this is the context 是您的问题。这是工作示例：

// MARK: MOCKS FOR MODELS
struct ProfileViewModel: Hashable 
    let id = UUID()
    let name: String


class CoreDataManager 
    static let shared = CoreDataManager()

    func getConfigurations() -> [ProfileViewModel] 
        return [ProfileViewModel(name: "first"), ProfileViewModel(name: "second"),  ProfileViewModel(name: "third")]
    


// MARK: changed class because it's not even working because of lack of code
class ProfilesListViewModel: ObservableObject 

    @Published var profiles: [ProfileViewModel] = [ProfileViewModel]()
    static var addNewProfile = ProfileViewModel(name: "Add Configuration")

    init() 
        fetchAllProfiles()
    

    func fetchAllProfiles() 
        print("fetched")
        profiles.append(ProfilesListViewModel.addNewProfile) ///Add is first object
        self.profiles = CoreDataManager.shared.getConfigurations()
    



// MARK: the solution
struct SetConfiguration: View 

    @ObservedObject var profileListVM: ProfilesListViewModel = ProfilesListViewModel()
    @State private var selectedConfiguration = 0 ///show "Add" as initial state
    @State private var choosedConfiguration = 0

    var body: some View 

        VStack 

            HStack 

                Picker(selection: $selectedConfiguration.onChange(selectNewConfig), label: Text("Configuration")) 
                    ForEach(0 ..< self.profileListVM.profiles.count)  choice in
                        Text(self.profileListVM.profiles[choice].name).tag(choice)
                    
                
            

            Text("Selected item is: \(choosedConfiguration)")

        

    

    func selectNewConfig(_ newValue: Int) 
        print(newValue)
        withAnimation 
            choosedConfiguration = newValue
        

    

提示

为避免日后误会：

您应该添加所有工作代码和链接，或者将其简化以明确您想要实现的目标。不是每个 Swift 开发者都知道extension Binding，所以他们只会说：onChange 永远不会工作，他们是对的；

格式化您的代码；

添加一些模型示例或删除/简化它们。

我相信，你不需要choosedConfiguration，你可以用这个做一些实验。