swift - AVCaptureVideo 不显示标签

Question

我正在尝试保留控制台中的对象，以将其显示为标签(分类器文本)。出现“UILabel.text must be used from main thread only”的警告。为什么项目显示为标签似乎有什么问题？

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

captureOutput(sampleBuffer, etc) 方法不在主线程上运行。所以你试图从一个不是主线程的线程更改标签。

解决方案是在主线程上安排工作，像这样:

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