ios – 类扩展崩溃中的Swift NSNotificationCenter观察者

2019年7月27日 150次阅读

我试图创建一个通用机制,可以对iOS中的键盘显示和隐藏作出反应.我提出了简单的协议及其扩展,它不包含真实的动画,但是从采用这个协议的对象中提取它们：

import UIKit

protocol KeyboardAnimatable {
    func keyboardWillShowAnimation() -> (() -> Void)?
    func keyboardWillHideAnimation() -> (() -> Void)?
}

extension KeyboardAnimatable where Self: UIViewController {

    func setupKeyboardNotifcationListeners() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name: UIKeyboardWillHideNotification, object: nil)
    }

    func removeKeyboardNotificationListeners() {
        NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillHideNotification, object: nil)
    }

    func keyboardWillShow(notification: NSNotification) {
        let userInfo = notification.userInfo as! Dictionary<String, AnyObject>
        let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSTimeInterval
        let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey]!.intValue
        let curveAnimationOption = UIViewAnimationOptions(rawValue: UInt(animationCurve))
        let options: UIViewAnimationOptions = [.BeginFromCurrentState, curveAnimationOption]

        if let animation = keyboardWillShowAnimation() {
            UIView.animateWithDuration(animationDuration, delay: 0, options: options, animations: animation, completion: nil)
        }
    }

    func keyboardWillHide(notification: NSNotification) {
        let userInfo = notification.userInfo as! Dictionary<String, AnyObject>
        let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSTimeInterval
        let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey]!.intValue
        let curveAnimationOption = UIViewAnimationOptions(rawValue: UInt(animationCurve))
        let options: UIViewAnimationOptions = [.BeginFromCurrentState, curveAnimationOption]

        if let animation = keyboardWillHideAnimation() {
            UIView.animateWithDuration(animationDuration, delay: 0, options: options, animations: animation, completion: nil)
        }
    }

}

我在扩展KeyboardAnimatable中明确使用where子句,其中Self：UIViewController将其缩小,以便在添加观察者时可以使用self.
现在我可以创建一个采用这种协议的视图控制器,例如键盘显示时更改约束：

import UIKit

class ViewController: UIViewController, KeyboardAnimatable {

    @IBOutlet weak var constraintYCenter: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()
        setupKeyboardNotifcationListeners()
    }

    func keyboardWillShowAnimation() -> (() -> Void)? {
        return {
            self.constraintYCenter.constant = 100
            self.view.layoutIfNeeded()
        }
    }

    func keyboardWillHideAnimation() -> (() -> Void)? {
        return nil
    }

//    func keyboardWillShow(notification: NSNotification) {
//        print("will show")
//    }
//    
//    func keyboardWillHide(notification: NSNotification) {
//        print("will hide")
//    }

    deinit {
        removeKeyboardNotificationListeners()
    }
}

但是,当我运行此代码时,应用程序崩溃并出现以下错误：

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', 
reason: '-[KeyboardAnimatableDemo.ViewController keyboardWillShow:]: 
unrecognized selector sent to instance 0x7fb429f192d0'

看起来我的视图控制器不使用在协议扩展中实现的keyboardWillShow：方法.
当我取消注释直接在ViewController中实现的这两个方法时,它们可以工作(打印日志),但是使用普通键盘动画制作工具的整个概念是无用的.

我认为在setupKeyboardNotifcationListeners()中可能会发生一些奇怪的事情,但即使我将其更改为例如func setupKeyboardNotifcationListeners(vc：UIViewController)并且在注册观察者时没有任何更改时使用vc而不是self.

一种可能的解决方案也可以是仅为采用该协议的控制器的子集创建UIViewController扩展.类似于这个扩展UIViewcontroller的地方Self：KeyboardAnimatable但是这个没有编译,我没有找到任何这样的定义的例子,所以它甚至可能在Swift中不可能.

有没有人试图实现类似的东西,他成功了？

最佳答案 我通过删除协议并为这些方法引入“空”实现来解决这个问题.现在,键盘的扩展直接扩展了UIViewController,所以它应该很容易使用.

代码依旧：https://gist.github.com/AdamSliwakowski/6fa1e920254ce584d203

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