swift - 条件绑定(bind)的初始化程序必须具有可选类型，而不是 'Todo?.Type'

Question

正在编写一个有点旧的教程，需要帮助弄清楚如何在没有可选类型的情况下进行初始化

var resultsController: NSFetchedResultsController<Todo>!
let coreDataStack = CoreDataStack()



override func viewDidLoad() {
    super.viewDidLoad()
    //Request
    let request: NSFetchRequest<Todo> = Todo.fetchRequest()
    let sortDesriptors = NSSortDescriptor(key: "date", ascending: true)

    //Init
    request.sortDescriptors = [sortDesriptors]
    resultsController = NSFetchedResultsController(
        fetchRequest: request,
        managedObjectContext: coreDataStack.managedContext,
        sectionNameKeyPath: nil,
        cacheName: nil)

    resultsController.delegate = self
    //Fetch
    do {
        try resultsController.performFetch()
    } catch {
        print("Perfom fetch error: \(error)")
    }


}


var managedContext: NSManagedObjectContext!
var todo = Todo?

if let todo = todo {                 <--- same issue here
    textView.text = todo.title
    textView.text = todo.title
    segmentedControl.selectedSegmentIndex = Int(todo.priority)




if let todo = todo {                 //<-- need help here.
    todo.title = title
    todo.priority = Int16(segmentedControl.selectedSegmentIndex)
} else {
    let todo = Todo(context: managedContext)
    todo.title = title
    todo.priority = Int16(segmentedControl.selectedSegmentIndex)
    todo.date = Date()
}

Initializer for conditional binding must have Optional type, not 'Todo?.Type'

不断收到此错误消息

Answer 1

您需要通过 var todo = Todo(parameter1Name: Parameter1Type,parameter2Name: Parameter2Type) 初始化 todo。您还可以通过 var todo: Todo? 声明 Todo 的可选实例，或通过 var todo: Todo! 隐式解包可选实例并设置此值之后。可选类型可以在这里理解:What does an exclamation mark mean in the Swift language?

var managedContext: NSManagedObjectContext!

//Option 1:
var todo = Todo()

//Option 2:
var optionalTodo: Todo?

optionalTodo = Todo()

if let todo = todo {
    textView.text = todo.title
    textView.text = todo.title
    segmentedControl.selectedSegmentIndex = Int(todo.priority)
    todo.title = title
    todo.priority = Int16(segmentedControl.selectedSegmentIndex)
} else {
    let todo = Todo(context: managedContext)
    todo.title = title
    todo.priority = Int16(segmentedControl.selectedSegmentIndex)
    todo.date = Date()
}