问题描述
我有一个带有核心数据模型的SwiftUI应用，其组织方式如下：
这是Task类扩展
extension Task {
@nonobjc public class func fetchRequest() -> NSFetchRequest<Task> {
return NSFetchRequest<Task>(entityName: "Task")
}
@NSManaged public var taskID: UUID
@NSManaged public var name: String
@NSManaged public var descr: String
@NSManaged public var type: String
@NSManaged public var date: Date
@NSManaged public var priority: Int
@NSManaged public var isCompleted: Bool
@NSManaged public var notificationID: UUID
@NSManaged public var subject: Subject
}
这是Subject类的扩展名：
extension Subject {
@nonobjc public class func fetchRequest() -> NSFetchRequest<Subject> {
return NSFetchRequest<Subject>(entityName: "Subject")
}
@NSManaged public var name: String
@NSManaged public var icon: String
@NSManaged public var color: UIColor
@NSManaged public var subjectID: UUID
@NSManaged public var tasks: NSSet?
public var taskArray: [Task] {
let set = tasks as? Set<Task> ?? []
return set.sorted {
$0.name < $1.name
}
}
}
// MARK: Generated accessors for tasks
extension Subject {
@objc(addTasksObject:)
@NSManaged public func addToTasks(_ value: Task)
@objc(removeTasksObject:)
@NSManaged public func removeFromTasks(_ value: Task)
@objc(addTasks:)
@NSManaged public func addToTasks(_ values: NSSet)
@objc(removeTasks:)
@NSManaged public func removeFromTasks(_ values: NSSet)
}
这是我创建新Task对象的视图：
struct NewTask: View {
// MARK: - Variables
@Binding var showSheet: Bool // To close the sheet view and go back to home
@State private var closeAlert: Bool = false // Close alert trigger
@State private var name: String = "" // Task's name
@State private var type: TaskType = TaskType.Homework // Task's type
@State private var subject = Subject() // Task's subject
@State private var description: String = "" // Task's description
@State private var priority: Int = 1 // Task's priority
@State private var date: Date = Date() // Task's date
@State private var notificationEnabled: Bool = UserDefaults.standard.bool(forKey: "notificationsEnabled")
@Environment(\.managedobjectContext) var moc // Managed Object Context for Core Data managing
@FetchRequest(entity: Subject.entity(),sortDescriptors: []) var subjects: FetchedResults<Subject>
init() {
self.subject = subjects[0]
}
// MARK: - View body
var body: some View {
NavigationView {
Form {
// Name input
TextField("app.inputTask.name",text: $name)
// Description input
TextField("app.inputTask.description",text: $description)
// Priority input
HStack {
Stepper("app.inputTask.priority",value: $priority,in: 1...3)
Text(String(priority)).padding(.leading,10)
}
// Type input
Picker(selection: $type,label: Text("app.inputTask.type")) {
ForEach(TaskType.allCases,id: \.self) {
Text(LocalizedStringKey($0.rawValue))
}
}
// Subject selection
Picker(selection: $subject,label: Text("app.inputTask.subject")) {
ForEach(self.subjects,id: \.subjectID) { subject in
Text(subject.name)
}
}
// Date picker for date
DatePicker(LocalizedStringKey("app.inputTask.date"),selection: $date,in: Date()...,displayedComponents: [.date,.hourAndMinute])
Button(action: {
print("Materie:")
//print(subjects)
},label: {
Text("Testing")
})
}
.alert(isPresented: $closeAlert) {
Alert(title: Text("app.warning"),message: Text("app.warning.discardChanges"),primaryButton: .default(Text("app.buttons.confirm"),action: {
self.showSheet.toggle()
}),secondaryButton: .default(Text("app.buttons.cancel")))
}
.navigationBarTitle("app.tasks.newTask")
.navigationBarItems(leading: HStack {
Button(action: {
if !self.name.isEmpty || !self.description.isEmpty {
self.closeAlert.toggle()
} else {
self.showSheet.toggle()
}
}) {
Text("app.buttons.close").foregroundColor(Color.red).bold()
}
},trailing: HStack {
Button(action: {
// Create and save the object
let task = Task(context: self.moc)
task.name = self.name
task.descr = self.description
task.priority = self.priority
task.type = self.type.rawValue
task.date = self.date
task.taskID = UUID()
task.notificationID = UUID()
// Relationship
task.subject = self.subject
subject.addToTasks(task)
// Schedule the notification for the task
if self.notificationEnabled == true {
scheduleNotification(title: name,body: description,date: date,notifUUID: task.notificationID)
}
// Close the new task view
self.showSheet.toggle()
}) {
Text("app.buttons.save").bold()
}
.disabled(self.name.isEmpty == true)
})
}
}
}
我要做的就是创建任务对象，并通过它们之间的关系将其链接到主题。 但是，当我保存新的Task对象时，出现错误“由于未捕获的异常'NSinvalidargumentexception'而终止应用程序”，原因：'-[Subject addTasksObject：]：无法识别的选择器发送到实例0x60000293cb00' 以NSException类型的未捕获异常终止。”
我正在使用Xcode 12 beta，但我不认为这是一个错误，我认为在创建任务对象后建立关系时做错了事
解决方法
原因是在@State private var subject初始化中-您不能这样做，因为Subject()无效-它应该与上下文一起使用，但是上下文尚不可用，并且在{中没有更新{1}}，因为获取请求尚未在初始化中执行，所以状态保持无效。
这里是解决此问题的一种可行方法（未经测试-由于代码不可测试，因此您可能需要修复编译器警告/错误）
请注意init声明/设置/使用位置。
subject