Swift 警告信息不明确

Question

你能给我解释一下这个警告消息的意思吗？

let x = cell.backgroundView!.layer.sublayers as! [CALayer]

Forced cast from '[CALayer]?' to '[CALayer]' only unwraps optionals; did you mean to use '!'?

Answer 1

使用强制转换没有意义。 sublayers returns 一个可选数组。您应该安全地打开可选数组。

if let sublayers = cell.backgroundView?.layer.sublayers {
    // do something with sublayers (which is a non-optional [CALayer])
}

还要注意在 backgroundView 之后使用 ? 而不是 !。

请花时间阅读 relevant sections in the Swift book. Otherwise your app is going to crash. See 了解有关该结果的大量详细信息，学习如何正确使用可选值。