在展开可选值keyboardWillShow时意外地发现了nil

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下面的代码在调用keyboardWillShowNotification时运行：

I have this code below which runs when the keyboardWillShowNotification is called:

func keyboardWillShow(_ notification: Notification) { //ERROR IN THE LINE BELOW keyboard = (notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as AnyObject).cgRectValue animaton = (notification.userInfo?[UIKeyboardAnimationDurationUserInfoKey] as AnyObject).doubleValue UIView.animate(withDuration: 0.4, animations: { () -> Void in self.scrollView.frame.size.height = self.scrollViewHeight - self.keyboard.height }) }

我在第二行收到错误说：在展开可选值时意外发现nil 。基本上每当我点击其中一个textFields时，都会调用键盘的这个通知，并且 keyboardWillShow 中的代码将会运行。我知道我把 if ... let 语句，但我想知道为什么我这样做为nil。

I am getting an error on the second line saying: unexpectedly found nil while unwrapping an Optional value. Basically whenever I click on one of the textFields this notification for the keyboard will be called and the code in keyboardWillShow will run. I know I put if...let statements but I want to know why I am getting nil for this.

我不知道我是如何得到此错误或如何调试它。是因为我是从模拟器运行的吗？

I am not sure how I am getting this error or how to debug it either. Is it because I am running it from the simulator?

这是打印notification.userInfo给出的内容：

Here is what printing the notification.userInfo gives:

可选（[AnyHashable（UIKeyboardFrameEndUserInfoKey）：NSRect：{{0,315}，{320,253}}，AnyHashable（UIKeyboardIsLocalUserInfoKey）：1，AnyHashable（UIKeyboardBoundsUserInfoKey）： NSRect：{{0,0}，{320,253}}，AnyHashable（UIKeyboardAnimationCurveUserInfoKey）：7，AnyHashable（UIKeyboardCenterBeginUserInfoKey）：NSPoint：{160,694.5}，AnyHashable（UIKeyboardCenterEndUserInfoKey）：NSPoint：{ 160,441.5}，AnyHashable（UIKeyboardFrameBeginUserInfoKey）：NSRect：{{0,568}，{320,253}}，AnyHashable（UIKeyboardAnimationDurationUserInfoKey）：0.25]）

Optional([AnyHashable("UIKeyboardFrameEndUserInfoKey"): NSRect: {{0, 315}, {320, 253}}, AnyHashable("UIKeyboardIsLocalUserInfoKey"): 1, AnyHashable("UIKeyboardBoundsUserInfoKey"): NSRect: {{0, 0}, {320, 253}}, AnyHashable("UIKeyboardAnimationCurveUserInfoKey"): 7, AnyHashable("UIKeyboardCenterBeginUserInfoKey"): NSPoint: {160, 694.5}, AnyHashable("UIKeyboardCenterEndUserInfoKey"): NSPoint: {160, 441.5}, AnyHashable("UIKeyboardFrameBeginUserInfoKey"): NSRect: {{0, 568}, {320, 253}}, AnyHashable("UIKeyboardAnimationDurationUserInfoKey"): 0.25])

推荐答案

来自文档：

let UIKeyboardFrameEndUserInfoKey: String

描述

Description

包含CGR的NSValue对象的键在屏幕坐标中标识键盘的结束帧

The key for an NSValue object containing a CGRect that identifies the end frame of the keyboard in screen coordinates

您的第二个键：

let UIKeyboardAnimationDurationUserInfoKey: String

描述包含的双精度的NSNumber对象的键，以秒为单位标识动画的持续时间。

Description The key for an NSNumber object containing a double that identifies the duration of the animation in seconds.

所以你需要将第一个转换为NSValue，将第二个转换为NSNumber：

So you need to cast the first one to NSValue and the second one to NSNumber:

func keyboardWillShow(_ notification: Notification) { print("keyboardWillShow") guard let userInfo = notification.userInfo else { return } keyboard = (userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue animaton = (userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSNumber).doubleValue // your code }