1.需求背景

iOS15上有一个非常好用的scan text (也可以叫live text)功能，如果能加上，用于扫描文本OCR（光学字符识别Optical Character Recognition），直接插入到textField里还是很方便的。

ios15-iphone12-pro-photos-copy-text.png

2.为什么目前不支持？

因为我用的自定义textField，没有针对scan text进行适配。我查阅了很多关于iOS15 OCR的资料。但是给textField长按菜单，加上scan text的内容没有找到，大体都说自定义长按菜单需要在

override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool

这个函数里去添加对应的action，然后

override func target(forAction action: Selector, withSender sender: Any?) -> Any?

这个函数里也要去做对应方法的实现，才能有对应的功能。

那么scan text对应的是哪个selector方法呢？

UIResponderStandardEditActions这个类里，并没有看到和OCR或者scan text相关的方法。然后我翻阅官方文档，找到了个很类似OCR的API

extension UIResponder {
    @available(iOS 15.0, *)
    open func captureTextFromCamera(_ sender: Any?)
}

试了下，果然就是这个玩意儿

所以如果你要你的自定义textField或者textview拥有scan text OCR的能力，那么应该如下实现。

3.实现

override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
    if #available(iOS 15.0, *) {
        if action == #selector(UIResponderStandardEditActions.paste(_:)) ||
            action == #selector(UIResponder.captureTextFromCamera(_:)){
            return true
        }
    } else {
        return super.canPerformAction(action, withSender: sender)
    }
    return super.canPerformAction(action, withSender: sender)
}

override func target(forAction action: Selector, withSender sender: Any?) -> Any? {
    if #available(iOS 15.0, *) {
        if action == #selector(UIResponderStandardEditActions.paste(_:)) ||
            action == #selector(UIResponderStandardEditActions.select(_:)) ||
            action == #selector(UIResponderStandardEditActions.selectAll(_:)) ||
            action == #selector(UIResponder.captureTextFromCamera(_:)) {
            return super.target(forAction: action, withSender: sender)
        }
    } else {
        // Fallback on earlier versions
        if action == #selector(UIResponderStandardEditActions.paste(_:)) ||
            action == #selector(UIResponderStandardEditActions.select(_:)) ||
            action == #selector(UIResponderStandardEditActions.selectAll(_:))
            {
            return super.target(forAction: action, withSender: sender)
        }
    }
    return nil
}

4.限制

4.1 版本和设备限制

只支持iOS15+，且iPhone Xs及以后的设备。如下是官方说明

For this property to be true, the device must have the A12 Bionic chip or later.

所以我们需要判断iOS 系统版本是iOS15，且支持OCR。

4.2 如何判断是否支持live text

一种是ImageAnalyzer.isSupported，如果是iOS 16就用这个判断，需要引入import VisionKit 这个visionKit。

另一种是利用实例化方法， canPerformAction(_:withSender:) ，官方的说法如下：

To determine whether the data scanner runs on the user’s device, pass captureTextFromCamera(_:) to the canPerformAction(_:withSender:) method.

例如

if UITextField().canPerformAction(#selector(UIResponder.captureTextFromCamera(_:)), withSender: self) { ... }

我之前以为直接用button的实例，来判断就可以了，居然不生效。一直返回false，我还不清楚说明原因。但是用上面这种，直接声明一个UITextField的实例来判断，就正常了，真的神奇。如果是在UIController里面，用下面的代码也可以：

if #available(iOS 15.0, *), self.canPerformAction(#selector(UIResponder.captureTextFromCamera(_:)), withSender: self) {
    print("support live text")
    button.addTarget(self, action: #selector(UIResponder.captureTextFromCamera(_:)), for: .touchUpInside)
} else {
    print("this device is not support live text")
}

所以这个条件，也是有点迷。

5.扩展运用 -- 如何自定义一个按钮，调用scan text识别文字功能？

自定义的按钮，和textField最大的不同，就是textField默认遵循了UIKeyInput or UITextInput 这两个中的某个协议，所以我们自定定义的按钮，那么我们要自己去遵循至少，这两个之一的协议，然后实现对应的代理方法，否则会崩溃。官方说明如下：

To receive callbacks from the data scanner, the responder should conform to either the UIKeyInput or UITextInput protocol. If it conforms to UIKeyInput, the scanner calls the insertText: protocol method. If it conforms to UITextInput, the scanner calls the setMarkedText(_:selectedRange:) and unmarkText() protocol methods.

class ViewController: UIViewController, UIKeyInput {
        var hasText: Bool = false
        
    override func viewDidLoad() {
        super.viewDidLoad()
        let button = UIButton.init(frame: CGRect(x: 100, y: 200, width: 100, height: 100))
                if #available(iOS 15.0, *), self.canPerformAction(#selector(UIResponder.captureTextFromCamera(_:)), withSender: self) {
            print("support live text")
            button.addTarget(self, action: #selector(UIResponder.captureTextFromCamera(_:)), for: .touchUpInside)
        } else {
            print("this device is not support live text")
        }
        button.backgroundColor = .red
        view.addSubview(button)
    }
    
    func deleteBackward() {
        
    }
    
    func insertText(_ text: String) {
        //ORC scan text的 insert Text 按钮回调
        print("OCR 扫描到的文字是: \(text)")
        labelTest.text = text
    }
}

参考文献：

https://developer.apple.com/documentation/uikit/uiresponder/3778577-capturetextfromcamera?changes=_5

https://developer.apple.com/documentation/visionkit/imageanalyzer/3974561-issupported

https://stackoverflow.com/questions/69702884/how-to-know-a-device-is-available-to-use-capturetextfromcamera-api/73995804#73995804