iosswiftfirebasefirebase-mlkit

Firebase MLKit Text Recognition Error


I'm trying to OCR my image using Firebase MLKit but it fails and return with error

Text detection failed with error: Failed to run text detector because self is nil.

/// Detects texts on the specified image and draws a frame for them.
func detectTexts() {
    let image = #imageLiteral(resourceName: "testocr")
    // Create a text detector.
    let textDetector = vision.textDetector()  // Check console for errors.

    // Initialize a VisionImage with a UIImage.
    let visionImage = VisionImage(image: image)
    textDetector.detect(in: visionImage) { (features, error) in
        guard error == nil, let features = features, !features.isEmpty else {
            let errorString = error?.localizedDescription ?? "No results returned."
            print("Text detection failed with error: \(errorString)")
            return
        }

        // Recognized and extracted text
        print("Detected text has: \(features.count) blocks")
        let resultText = features.map { feature in
            return "Text: \(feature.text)"
            }.joined(separator: "\n")
        print(resultText)
    }
}

Solution

  • It looks like you need to keep a strong reference to textDetector, otherwise the detector gets released before the completion block can be called.

    Changing your code a bit:

    var textDetector: VisionTextDetector?   // NEW
    
    /// Detects texts on the specified image and draws a frame for them.
    func detectTexts() {
        // ... truncated ...
        textDetector = vision.textDetector()   // NEW
        let visionImage = VisionImage(image: image)
        textDetector?.detect(in: visionImage) { (features, error) in   // NEW
            // Callback implementation
        }
    }
    

    You can also unwrap it to make sure it's not nil after you assign it:

    guard let textDetector = textDetector else { 
        print("Error: textDetector is nil.")
        return
    }
    

    I hope that helps!