AVCaptureVideo未顯示標籤

Question

我試圖保留控制檯中的對象以顯示爲標籤（classifierText）。出現「僅從主線程使用UILabel.text」的警告。什麼似乎是問題，爲什麼項目被顯示爲標籤？

var previewLayer: AVCaptureVideoPreviewLayer! 

let classifierText: UILabel = { 
    let classifier = UILabel() 
    classifier.translatesAutoresizingMaskIntoConstraints = false 
    classifier.textColor = .black 
    classifier.font = UIFont(name: "Times-New-Roman", size: 10) 
    classifier.textAlignment = .center 
    return classifier 
}() 

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) { 
    guard let pixelBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return } 
    guard let model = try? VNCoreMLModel(for: Resnet50().model) else { return } 
    let request = VNCoreMLRequest(model: model) { (finishedReq, err) in 
    let results = finishedReq.results as? [VNClassificationObservation] 
    let firstObservation = results!.first 
    self.classifierText.text = "\(firstObservation!.identifier as String)" 

Answer 1

方法captureOutput(sampleBuffer, etc)不在主線程上運行。所以你試圖從一個不是主線程的線程改變標籤。

的解決方法是安排工作的主線程，就像這樣：

DispatchQueue.main.async { 
    self.classifierText.text = "\(firstObservation!.identifier as String)" 
}