我尝试在 SwiftUI 中遵循 MVVM 模式，但遇到了核心数据和获取请求的问题。
我看过的所有视频和读过的文章在视图中都有一个@FetchRequest，用于访问和修改核心数据。
如何将其放入 SettingsVCModel 中？我似乎无法弄清楚，因此我将获取请求保留在视图结构（SettingsVC）内并在那里使用它。
但是到目前为止，这都是通过按钮来执行操作的。现在我需要使用一个切换按钮来完成此操作，该切换按钮只有一个与之关联的绑定变量，并且没有像按钮那样的操作。
我在 SettingsVCModel 内的 @Published bio 上尝试了 didSet 方法，但是您无权访问获取请求。
我正在使用的代码如下：
struct SettingsVC: View {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(fetchRequest: UserSettings.getUserSettings()) var userSettings : FetchedResults<UserSettings>
@ObservedObject var model = SettingsVCModel()
var body: some View {
NavigationView {
Form{
Section(header: Text("Application")){
Toggle(isOn: $model.bio, label: {Text(model.determineBiometricType())})
Picker(selection: $model.unitSelection, label: Text("Units")) {
Text("Imperial").tag(0)
Text("Metric").tag(1)
}
SettingsButton(toggleButton: $model.openSettings, title: "System Authorizations")
}
Section(header: Text("Feedback")){
NavigationLink(destination: ContactVC()){
Text("Contact Me")
}
SettingsButton(toggleButton: $model.rateApp, title: "Please Rate Body Insights")
SettingsButton(toggleButton: $model.tellAFriend, title: "Tell a Friend")
}
Section(header: Text("General")){
NavigationLink(destination: AboutVC()){
Text("About")
}
SettingsButton(toggleButton: $model.openPrivacyPolicy, title: "Privacy Policy", openPrivacyPolicy: true)
}
}
.onAppear{
self.model.bio = self.userSettings.first!.useBiometricUnlock
self.model.unitSelection = self.userSettings.first!.usesMetric ? 1 : 0
}
.navigationBarTitle("Settings")
.sheet(isPresented: $model.tellAFriend, content: {
ShareSheetView(activityItems: ["Hey, check out this cool app! https://apps.apple.com/uy/app/body-insights/id1397531585"])
})
}
}
}
final class SettingsVCModel : ObservableObject{
@Published var unitSelection = 0
@Published var tellAFriend = false
@Published var openPrivacyPolicy = false
@Published var bio = false
@Published var openSettings = false {
didSet{
if openSettings{
openAppSettingsApp()
openSettings = false
}
}
}
@Published var rateApp = false {
didSet{
if rateApp{
openRateApp()
rateApp = false
}
}
}
func openRateApp() {
let appID = "1397531585"
let urlString = "https://itunes.apple.com/us/app/appName/id\(appID)?mt=8&action=write-review"
let url = URL(string: urlString)!
UIApplication.shared.open(url, options: [:], completionHandler: nil)
}
func openAppSettingsApp() {
guard
let settingsURL = URL(string: UIApplication.openSettingsURLString),
UIApplication.shared.canOpenURL(settingsURL)
else {
return
}
UIApplication.shared.open(settingsURL)
return
}
func determineBiometricType() -> String {
let authContext = LAContext()
let _ = authContext.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: nil)
switch(authContext.biometryType) {
case .none:
return "Not Avaliable"
case .touchID:
return "TouchID"
case .faceID:
return "FaceID"
@unknown default:
return "Not Avaliable"
}
}
}
public class UserSettings : NSManagedObject, Identifiable {
@NSManaged public var useBiometricUnlock : Bool
@NSManaged public var usesMetric : Bool
@NSManaged public var name : String
@NSManaged public var birthday : Date
@NSManaged public var age : Int
static func getUserSettings() -> NSFetchRequest<UserSettings> {
let request : NSFetchRequest<UserSettings> = UserSettings.fetchRequest() as! NSFetchRequest<UserSettings>
request.sortDescriptors = []
return request
}
static func save(){
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
do {
try context.save()
} catch{
print(error)
}
}
static func preloadData(){
let preloadKey: String = "preloadKey"
let isPreloaded = UserDefaults.standard.bool(forKey: preloadKey)
if !isPreloaded {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let defaultSettings = UserSettings(context: context)
let deviceName = UIDevice.current.name
let firstName = deviceName.components(separatedBy: " ").first
let isMetric = NSLocale.current.usesMetricSystem
defaultSettings.name = firstName ?? ""
defaultSettings.useBiometricUnlock = false
defaultSettings.usesMetric = isMetric
defaultSettings.age = 0
defaultSettings.birthday = Date()
UserDefaults.standard.set(true, forKey: preloadKey)
UserSettings.save()
}
}
}
看来你只能在视图中使用 SwiftUI 的
FetchRequestDynamicProperty获取请求：
/// Property wrapper to help Core Data clients drive views from the results of
/// a fetch request. The managed object context used by the fetch request and
/// its results is provided by @Environment(\.managedObjectContext).
@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
@propertyWrapper public struct FetchRequest<Result> : DynamicProperty where Result : NSFetchRequestResult {
动态属性：
/// Represents a stored variable in a `View` type that is dynamically
/// updated from some external property of the view. These variables
/// will be given valid values immediately before `body()` is called.
@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
public protocol DynamicProperty {
/// Called immediately before the view's body() function is
/// executed, after updating the values of any dynamic properties
/// stored in `self`.
mutating func update()
}
我最终放弃了
EnvironmentObjectCoreData 可以被认为是 ViewModel 本身。我们在视图中使用 @FetchRequest 来“观察”CoreData 描述的模型发生的变化。如果您还将 CloudKit 与 CoreData 一起使用，那么当您的视图处于活动状态时，您的 @FetchRequest 也处于活动状态，并且来自 iCloud 的任何入站更改都将被“观察到”，并将导致您的视图更新。
如果您想从您自己构建的 ViewModel 中的 CoreData 获取数据，只需使用非 SwiftUI 函数即可。我今天刚刚在 ViewModel 中写了这个：
let request = API.fetchRequest()
let sort = NSSortDescriptor(keyPath: \API.priority, ascending: true)
request.sortDescriptors = [sort]
do {
if let apis = try container.viewContext.fetch(request) as? [API] {
logger.debug("APIs fetched: \(apis.count)")
self.apis = apis
}
} catch {
logger.debug("Fetch failed 😭")
}
就像这样，我将数据提取到我的 ViewModel 中，现在我可以将其分配给一些 @Published 属性。快乐编码！