Question

升级到1.2后，我遇到了编译错误：

NSDate?! is not convertible to NSDate

代码：

let dateCreated = photoCommentObjects[indexPath.row].createdAt as NSDate

其他尝试：

我也尝试过：

let dateCreated = photoCommentObjects[indexPath.row].createdAt as? NSDate

我收到错误：

Downcast from NSDate?! to 'NSDate' only unwraps optionals

Answer 1

这是一个类型问题。您有一个AnyObject类型的数组，但您无法在AnyObject上阅读该属性。

//sample data
class PhotoComment {
   let createdAt = NSDate()
}

let photoCommentObjects: [AnyObject] = [PhotoComment()]

//let's get the indexed object first and let's cast it from AnyObject
let photoComment = photoCommentObjects[indexPath.row] as! PhotoComment
//now trivially
let dateCreated = photoComment.createdAt

或

//let's cast the whole array first
let photoComments = photoCommentObjects as! [PhotoComment]
let dateCreated = photoComments[indexPath.row].createdAt

Answer 2

你试过吗？

let dateCreated = photoCommentObjects[indexPath.row].createdAt as! NSDate

自Sift 1.2起，您必须使用!明确标记强制转换。这提醒您，如果失败，您的应用程序将崩溃。

Answer 3

显然photoCommentObjects[indexPath.row].createdAt正在返回一种NSDate?!类型，它是一个隐式包含的可选项可选项。要打开它，首先使用NSDate?将结果强制转换为as以删除隐式包装的可选项，然后使用可选绑定来展开生成的NSDate?：

if let dateCreated = photoCommentObjects[indexPath.row].createdAt as NSDate? {
    // use dateCreated which is of type NSDate
}

结果是dateCreated将是普通NSDate。

或者，您可以使用：

if let temp = photoCommentObjects[indexPath.row].createdAt, dateCreated = temp {
    // each assignment unwraps one layer of Optional
    // use dateCreated which is of type NSDate
} else {
    println("something is nil")
}

Swift 1.2 NSDate？！不可转换为NSDate

其他尝试：

3 个答案: