How to check if there is no text in an Image--MLKit VisionCloudTextRecognizer

Question

I have a class called MLVision which handles the text recognition.

class MLVision {

    lazy var vision = Vision.vision()
    var textRecognizer: VisionTextRecognizer!
    var textArray = [] as Array<String>
    var lineText :String = ""

    func startRecognising(image : UIImage,completion: @escaping (_ result: [String]) -> ()){

        let visionImage = VisionImage(image: image)

        let options = VisionCloudTextRecognizerOptions()
        options.languageHints = ["en","hi"]
        textRecognizer = vision.cloudTextRecognizer(options: options)

        textRecognizer.process(visionImage, completion: { (features, error) in
            guard error == nil, let features = features else {
                print("No text Found!!")
                return
            }

            for block in features.blocks {
                for line in block.lines{


                    self.lineText = line.text
                    self.separate(lineText: self.lineText)

                }
            }
            completion(self.textArray)
        })
    }

    func separate(lineText : String){
        let separators = CharacterSet(charactersIn: (":)(,•/·]["))
        let ofWordsArray = lineText.components(separatedBy: separators)

        for word in ofWordsArray{

            let low = word.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
            if low != ""{
                textArray.append(low)
            }
        }
    }
}

And this is the that ViewController I call the Mlvision class.

let mlVision = MLVision()

override func viewDidLoad() {
        super.viewDidLoad()
    mlVision.startRecognising(image: croppedImage!){ result in

                self.textArray = result
                self.searchIngredients(textArray: self.textArray)
        }
}

So basically my app recognises text then separates it and pass it in an Array.

I want to handle if I check an image without text to show an alert. I know that the guard error == nil, let features = features else {return} handles it but I want to check it from my ViewController. Is there a way to do that?

Answer 1

if i got your question right - you just want to handle errors from recognition in the scope where you started it, if so than you can modify your code to below using Result.

// add your own Errors
enum RecognitionError: Error {
    case textNotFound
}

//modify `completion` closure by passing `Result` object instead of array
func startRecognising(image : UIImage,
                  completion: @escaping (_ result: Result<[String], RecognitionError>) -> ()){

    let visionImage = VisionImage(image: image)

    let options = VisionCloudTextRecognizerOptions()
    options.languageHints = ["en","hi"]
    textRecognizer = vision.cloudTextRecognizer(options: options)

    textRecognizer.process(visionImage, completion: { (features, error) in
        guard error == nil, let features = features else {
            print("No text Found!!")
            completion(.failure(.textNotFound))
            return
        }

        for block in features.blocks {
            for line in block.lines{


                self.lineText = line.text
                self.separate(lineText: self.lineText)

            }
        }
        completion(.success(self.textArray))
    })
}

And handle it in your ViewController:

override func viewDidLoad() {
    super.viewDidLoad()
    mlVision.startRecognising(image: croppedImage!){ result in
        switch result {

        case .success(let array):
            self.textArray = result
            self.searchIngredients(textArray: self.textArray)

        case .failure(let error):
            print(error)
        }
    }
}