Xcode 7 中的向下转换错误

Question

在 xcode 6 中，此代码运行良好，但在 Xcode 7GM 中，我收到一条错误消息：

Downcast from ‘[UILocalNotification]? to ‘[UILocalNotification]’ only unwraps optionals; did you mean to use ‘!’?

错误发生在我放了两个星号的那一行。在Xcode中，as!部分的a下面也有一个小红三角。

func removeItem(item: TodoItem) {
    **for notification in (UIApplication.sharedApplication().scheduledLocalNotifications as! [UILocalNotification]) { // loop through notifications...
        if (notification.userInfo!["UUID"] as! String == item.UUID) { // ...and cancel the notification that corresponds to this TodoItem instance (matched by UUID)
            UIApplication.sharedApplication().cancelLocalNotification(notification) // there should be a maximum of one match on UUID
            break
        }
    }

Answer 1

在Xcode 6中scheduledLocalNotifications声明为[AnyObject]!（需要向下转换）。
在 Xcode 7 中，scheduledLocalNotifications 被声明为 [UILocalNotification]?（只需要展开）

我建议使用可选绑定

func removeItem(item: TodoItem) {
  if let scheduledLocalNotifications = UIApplication.sharedApplication().scheduledLocalNotifications {
   for notification in scheduledLocalNotifications { // loop through notifications...
    if (notification.userInfo!["UUID"] as! String == item.UUID) { // ...and cancel the notification that corresponds to this TodoItem instance (matched by UUID)
        UIApplication.sharedApplication().cancelLocalNotification(notification) // there should be a maximum of one match on UUID
        break
    }
  }
}

Xcode 7 中的向下转换错误

Downcast error in Xcode 7

xcode7

downcast