条件绑定的初始化程序必须具有可选类型，而不是“日期”

Question

Xcode 报错

但我不知道会发生什么。我一直在寻找，我认为这可能是关于铸造和可选的。第一个给出 Initializer for conditional binding must have Optional type, not 'Date' 第二个和第三个给出 Initializer for conditional binding must have Optional type, not 'Double'

for article in (topic.articleArrays ?? nil)!{
            if let articleId = article.id,
            let articleHeadline = article.headline,
            let articleSummary = article.summary,
            let articleCity = article.city,
            let articleState = article.state,
            let articleDateretrieved = article.dateRetrieved,
            let articlePublisher = article.publisher,
            let articleLatitude = article.latitude,
            let articleLongitude = article.longitude,
            let articleRawBaseUrl = article.rawBaseUrl,
            let articleRawUrl = article.rawUrl {
                editedArticles?.append(NewsArticle(id: articleId, headline: articleHeadline, publisher: articlePublisher, summary: articleSummary, rawUrl: articleRawUrl, rawBaseUrl: articleRawBaseUrl, retrieved_date: articleDateretrieved, city: articleCity, state: articleState, latitude: articleLatitude, longitude: articleLongitude))
            }
        }

ediedArticles 的结构是我在下面列出的 NewsArticle

struct NewsArticle {
var id: String
var headline: String
var publisher: String
var summary: String
var rawUrl: String
var rawBaseUrl: String
var retrieved_date: Date
var city: String
var state: String
var latitude: Double
var longitude: Double
init(id: String, headline: String, publisher: String, summary: String, rawUrl: String, rawBaseUrl: String, retrieved_date: Date, city: String, state: String, latitude: Double, longitude: Double) {
    self.id = id
    self.headline = headline
    self.publisher = publisher
    self.summary = summary
    self.rawUrl = rawUrl
    self.rawBaseUrl = rawBaseUrl
    self.retrieved_date = retrieved_date
    self.city = city
    self.state = state
    self.latitude = latitude
    self.longitude = longitude
    }
}

topic.articlesArray 有不同的数据结构类型 SavedArticle (CoreData)

var articleArrays: [SavedArticle]? {
    return self.articles?.allObjects as? [SavedArticle]
}

并拥有 SavedArticle-CoreDataClass

var dateRetrieved: Date {
    get {
        return retrieved_date as Date
    }
    set(newDate) {
        retrieved_date = newDate as NSDate
    }
}

// TODO: Figured it out how to stored corrdinates in [Double]

convenience init?(id: String, headline: String, publisher: String, summary: String, retrieved_date: Date, city: String, state: String, latitude: Double, longitude: Double) {

    guard let context = NaberCoreDataHandler.sharedInstance.managedContext else { return nil }
    self.init(entity: SavedArticle.entity(), insertInto: context)

    self.id = id
    self.headline = headline
    self.publisher = publisher
    self.summary = summary
    self.dateRetrieved = retrieved_date
    self.city = city
    self.state = state
    self.latitude = latitude
    self.longitude = longitude
}

具有以下 SavedArticle-CoreDataProperties

@NSManaged public var city: String?
@NSManaged public var headline: String?
@NSManaged public var id: String?
@NSManaged public var publisher: String?
@NSManaged public var rawBaseUrl: String?
@NSManaged public var rawUrl: String?
@NSManaged public var retrieved_date: NSDate
@NSManaged public var state: String?
@NSManaged public var summary: String?
@NSManaged public var latitude: Double
@NSManaged public var longitude: Double
@NSManaged public var topics: SavedTopic?

如果有人能帮我找出问题所在，那就太好了。我一整天都在努力，没有任何帮助。谢谢！ :)

Answer 1

article.dateRetrieved、article.latitude 和 article.longitude 不是可选项。他们不是用 ?在它们的类型名称之后，所以它们永远不能为零。因此没有必要——事实上这是一个错误——尝试用“if let”语句解开它们。

删除编译器抱怨的三行代码。

当您创建 NewsArticle 并将其附加到editedArticles 时，您可以将文章的这些属性直接传递给 NewsArticle 的构造函数。

Answer 2

if let（和guard let）只能用于解开可选值。您可以使用常规的 let 语句在单独的行上分配这些值，或者直接将它们传递给函数，因为它们不需要解包。