如何在 Swift 5 中为多种类型进行扩展

Question

我有以下扩展，我希望它可用于 UITextView 和 UILabel。

extension UITextView {
    func setTextWithTypeAnimation(typedText: String, characterDelay: TimeInterval = 2.5) {
        text = ""
        var writingTask: DispatchWorkItem?
        writingTask = DispatchWorkItem { [weak weakSelf = self] in
            for character in typedText {
                DispatchQueue.main.async {
                    weakSelf?.text!.append(character)
                }
                Thread.sleep(forTimeInterval: characterDelay/100)
            }
        }

        if let task = writingTask {
            let queue = DispatchQueue(label: "typespeed", qos: DispatchQoS.userInteractive)
            queue.asyncAfter(deadline: .now() + 0.05, execute: task)
        }
    }
}

我尝试将类型设置为 UIView 在这里找到：Stack Overflow: Single extension for UITextView and UITextField in Swift

extension UIView  {
    func setTextWithTypeAnimation(typedText: String, characterDelay: TimeInterval = 2.5) {
        if self is UILabel || self is UITextView {
            text = ""
            var writingTask: DispatchWorkItem?
            writingTask = DispatchWorkItem { [weak weakSelf = self] in
                for character in typedText {
                    DispatchQueue.main.async {
                        weakSelf?.text!.append(character)
                    }
                    Thread.sleep(forTimeInterval: characterDelay/100)
                }
            }

            if let task = writingTask {
                let queue = DispatchQueue(label: "typespeed", qos: DispatchQoS.userInteractive)
                queue.asyncAfter(deadline: .now() + 0.05, execute: task)
            }
        }
    }
}

这当然行不通，因为 UIView 没有文本属性，所以我收到以下错误：

Use of unresolved identifier 'text'

我该如何解决这个问题？

Answer 1

这当然不行，因为 UIView 没有 text 属性

这正是您要考虑的部分。为了编写这个方法，你需要什么？两件事：它需要一个text 属性。它必须是一个类类型（因为你使用了weak 修饰符）。就这么说吧。

protocol TypeAnimated: AnyObject {
    var text: String? { get set }
}

除了由于历史原因，UITextView 有一个String! 而UILabel 有一个String?。这很令人沮丧，但我们可以通过一个新属性来连接两者：

protocol TypeAnimated: AnyObject {
    var animatedText: String { get set }
}

现在，给定该协议，您可以编写方法：

extension TypeAnimated  {
    func setTextWithTypeAnimation(typedText: String, characterDelay: TimeInterval = 2.5) {
        animatedText = ""
        var writingTask: DispatchWorkItem?
        writingTask = DispatchWorkItem { [weak weakSelf = self] in
            for character in typedText {
                DispatchQueue.main.async {
                    weakSelf?.animatedText!.append(character)
                }
                Thread.sleep(forTimeInterval: characterDelay/100)
            }
        }

        if let task = writingTask {
            let queue = DispatchQueue(label: "typespeed", qos: DispatchQoS.userInteractive)
            queue.asyncAfter(deadline: .now() + 0.05, execute: task)
        }
    }
}

现在，您只需标记任何想要符合此协议的类型，它们就会获得扩展名。

extension UILabel: TypeAnimated {
    var animatedText: String {
        get { return text ?? "" }
        set { text = newValue }
    }
}

extension UITextView: TypeAnimated {
    var animatedText: String {
        get { return text ?? "" }
        set { text = newValue }
    }
}

---

作为旁注，每次执行时生成一个新队列几乎肯定不是您的意思。您可能应该将其设置为对主队列的一系列asyncAfter 调用，或使用计时器，或在asyncAfter 块内调用asyncAfter。但这一切都不会真正影响您的问题。

我没有对此进行测试，但这可能是我解决问题的方法：

extension TypeAnimated  {
    func setTextWithTypeAnimation(typedText: String, characterDelay: TimeInterval = 2.5/100) {
        func addNextCharacter(from string: Substring) {
            DispatchQueue.main.asyncAfter(deadline: .now() + characterDelay) { [weak self] in
                if let self = self, let nextChar = string.first {
                    self.animatedText.append(nextChar)
                    addNextCharacter(from: string.dropFirst())
                }
            }

        }

        animatedText = ""
        addNextCharacter(from: typedText[...])
    }
}