在解开可选值 keyboardWillShow 时意外发现 nil [英] unexpectedly found nil while unwrapping an Optional value keyboardWillShow

问题描述

我在下面有这个代码，当调用 keyboardWillShowNotification 时运行:

func keyboardWillShow(_ notification: Notification) {//错误在下一行键盘 = (notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as AnyObject).cgRectValueanimaton = (notification.userInfo?[UIKeyboardAnimationDurationUserInfoKey] as AnyObject).doubleValueUIView.animate(withDuration: 0.4, animations: { () -> Void inself.scrollView.frame.size.height = self.scrollViewHeight - self.keyboard.height})}

我在第二行收到一条错误消息:unexpectedly found nil while unwrapped an Optional value.基本上，每当我单击 textFields 之一时，都会调用此键盘通知，并且 keyboardWillShow 中的代码将运行.我知道我放了 if...let 语句，但我想知道为什么我的结果为零.

我不确定我是如何收到此错误或如何调试它的.是不是因为我是在模拟器上运行的?

这是打印notification.userInfo 给出的内容:

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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: {1160,}4AnyHashable("UIKeyboardFrameBeginUserInfoKey"): NSRect: {{0, 568}, {320, 253}}, AnyHashable("UIKeyboardAnimationDurationUserInfoKey"): 0.25])

解决方案

来自文档:

let UIKeyboardFrameEndUserInfoKey: String

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说明

一个 NSValue 对象的键，它包含一个标识以屏幕坐标表示的键盘结束帧

你的第二把钥匙:

let UIKeyboardAnimationDurationUserInfoKey: String

<块引用>

描述包含双精度值的 NSNumber 对象的键以秒为单位标识动画的持续时间.

因此您需要将第一个转换为 NSValue，将第二个转换为 NSNumber:

func keyboardWillShow(_ notification: Notification) {打印(键盘将显示")守卫让 userInfo = notification.userInfo else { return }键盘 = (userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValueanimaton = (userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSNumber).doubleValue//你的代码}

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
    }) 
}

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.

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?

Here is what printing the notification.userInfo gives:

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])

解决方案

From the docs:

let UIKeyboardFrameEndUserInfoKey: String 

Description

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

Your second key:

let UIKeyboardAnimationDurationUserInfoKey: String

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

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
}

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