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swift - 在我的 init() 方法中调用视图之前，我的 coreData 没有加载

问题描述

我正在使用此方法将状态值设置为我的 coreData 实体 UserSettings 中的值，以便可以在屏幕上显示它们。

获取 coreData 实体的最常见方法是使用获取请求，但由于某种原因，它没有加载值并说数组为空：

配置文件视图：

import HealthKit
import SwiftUI
import Combine //to use Just

struct ProfileView: View {
    
    @Environment(\.managedObjectContext) private var viewContext

    @ObservedObject var viewModel: AddViewModel = AddViewModel()
@FetchRequest(
            entity: UserSettings.entity(),
            sortDescriptors: [])
    private var userSettingEntity: FetchedResults<UserSettings>


init(){


let x = viewModel.fetchProgresses()
let y = userSettingEntity.count

print(y)
print(x.count)
if(!x.isEmpty){
    print(x[0].bmr)



userName = x[0].firstName!
  ageInputString = String(x[0].age)
  heightInputString = String(x[0].height)
  weightInputString = String(x[0].weight)
  selectedGender = Double(x[0].age)
  chosenActivityLevel = x[0].activityLevel!
  BMR = x[0].bmr
    
    }
}
   

    var body: some View {

    
    VStack{ //vertical stack for the form
        Form{
            Section{
                Text(String(BMR))
    }

Any help would be really useful :)

对于上下文，这是我的视图模型：

class AddViewModel: ObservableObject {
    
    @Published var userSettings = [UserSettings]()

    
    init() {
    //    print(fetchProgresses().count)

    }
    
    //Creating the data
    func addCalorieTrackerDate(id: UUID, firstName: String, height: Double, weight: Double, gender: String, age: Double, activityLevel: String, bmr: Double) {
        CoreDataManager.shared.addUserSettingsData(id: id, firstName: firstName, height: height, weight: weight, gender: gender, age: age, activityLevel: activityLevel, bmr: bmr) { (isAdded, error) in
            if let error = error {
                print(error)
            } else {
                print("Data has been added!")
                print(gender)
            }
        }
    }
    
    //fetching the data
    func fetchProgresses() -> [UserSettings] {
        CoreDataManager.shared.fetchCalorieTrackerData { (userSettings, error) in
            if let error = error {
                print(error)
            }
            if let userSettings = userSettings as? [UserSettings] {
                self.userSettings = userSettings
            }
        }
        return userSettings
    }

CoreDataManager.swift：

class CoreDataManager {
    
    static let shared: CoreDataManager = {
        let appDelegate = AppDelegate.instance!
        let instance = CoreDataManager(managedObjectContext: appDelegate.persistanceContainer.viewContext)
        return instance
    }()
    
    var managedContext: NSManagedObjectContext
    
  private init(managedObjectContext: NSManagedObjectContext) {
        managedContext = managedObjectContext
    }
}

//MARK:- CalorieTracker Insert/Update/Delete
extension CoreDataManager {
    func addUserSettingsData(id: UUID, firstName: String, height: Double, weight: Double, gender: String, age: Double, activityLevel: String, bmr: Double, completionHandler: @escaping (_ succeed: Bool, _ error: Error?) -> Void) {
        let userSettingsEntity = NSEntityDescription.insertNewObject(forEntityName: "UserSettings", into: managedContext) as? UserSettings
        userSettingsEntity?.id = id
        userSettingsEntity?.firstName = firstName
        userSettingsEntity?.height = height
        userSettingsEntity?.weight = weight
        userSettingsEntity?.gender = gender
        userSettingsEntity?.age = age
        userSettingsEntity?.activityLevel = activityLevel
        userSettingsEntity?.bmr = bmr
        
        do {
            try managedContext.save()
            completionHandler(true, nil)
        } catch let error {
            completionHandler(false, error)
        }
    }
    
    func fetchCalorieTrackerData(completionHandler: @escaping (_ succeed: Any?, _ error: Error?) -> Void) {
        var progresses = [UserSettings]()
        let progressRequest: NSFetchRequest<UserSettings> = NSFetchRequest<UserSettings>(entityName: "UserSettings")
        
        do {
            progresses = try managedContext.fetch(progressRequest)
            completionHandler(progresses, nil)
        } catch let error {
            completionHandler(nil, error)
        }
    }
    
    func deleteUserSettingData(){
        let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "UserSettings")
        let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
    
        do {
            try managedContext.execute(deleteRequest)
        } catch _ as NSError {
    }
    }
    
    
}

标签： swiftcore-dataswiftui

解决方案

您在不同的地方做类似的事情，所以最好重构它并拥有一个数据源。

在视图模型中进行更改fetchProgresses，因此它不会返回任何内容，因此您将从userSettings视图中使用已发布的属性。

然后在视图中删除获取请求和初始化内容，如前所述，从视图模型中获取数据

struct ProfileView: View {

    @ObservedObject var viewModel: AddViewModel = AddViewModel()

    var body: some View {
        VStack{  
            Form {
                Section {
                    Text(String(viewModel.userSettings.first?.bmr ?? 0))

由于您在这里使用的是表单而不是列表，因此您是否总是只在 UserSettings 数组中获得一项？如果是这样，那么您应该在视图模型中通过将发布的属性更改为来解决此问题

@Published var userSettings: UserSettings?

甚至更好，如果你想把它变成更正确的 MVVM，那么在 UserSettings 中为每个属性都有一个已发布的属性

@Published var firstName: String
@Published var bmr: String
...

那么您的视图代码会更简单

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