ios - 来自 AnyObject 的 Swift 类型转换

Question

我正在尝试从我的商店中获取数据，但出现以下错误:

“事件”与“AnyObject”不同

我有一个events 变量，它是一个Event 数组。我猜从获取请求返回的数据来自 AnyObject 类型。所以我尝试将其类型转换为 [Event] 但它不起作用，我也不知道为什么。

var events: [Event] = []

func loadDataFromDB() {
  let fetchRequest = NSFetchRequest(entityName: "Event")
  events = context?.executeFetchRequest(fetchRequest, error: nil) as [Event]
}

Answer 1

当涉及可选链时，这似乎是某种错误。使用这些替代方案来解决问题:

events = context?.executeFetchRequest(fetchRequest, error: nil) as [AnyObject]? as [Event]
events = (context?.executeFetchRequest(fetchRequest, error: nil))! as [Event]
events = context!.executeFetchRequest(fetchRequest, error: nil) as [Event]

为了安全起见，我建议使用:

if let result = context?.executeFetchRequest(fetchRequest, error: nil) {
    events = result as [Event]
}

如果有错误，executeFetchRequest 返回 nil。