自动对焦后拍照AVCapture

Question

我想这样做:当相机对焦时，应用程序会自动拍照。但我发现没有办法检测相机是否对焦。我正在使用AVFoundation拍照，我是iOS新手，不知道如何编码，有人能帮我解决这个问题吗？

Answer 1

import UIKit
import AVFoundation
class ViewController: UIViewController {
    let captureSession = AVCaptureSession()
    let stillImageOutput = AVCaptureStillImageOutput()
    var error: NSError?
    override func viewDidLoad() {
        super.viewDidLoad()
        let devices = AVCaptureDevice.devices().filter{ $0.hasMediaType(AVMediaTypeVideo) && $0.position == AVCaptureDevicePosition.Back }
        if let captureDevice = devices.first as? AVCaptureDevice  {

            captureSession.addInput(AVCaptureDeviceInput(device: captureDevice, error: &error))
            captureSession.sessionPreset = AVCaptureSessionPresetPhoto
            captureSession.startRunning()
            stillImageOutput.outputSettings = [AVVideoCodecKey:AVVideoCodecJPEG]
            if captureSession.canAddOutput(stillImageOutput) {
                captureSession.addOutput(stillImageOutput)
            }
            if let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession) {
                previewLayer.bounds = view.bounds
                previewLayer.position = CGPointMake(view.bounds.midX, view.bounds.midY)
                previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
                let cameraPreview = UIView(frame: CGRectMake(0.0, 0.0, view.bounds.size.width, view.bounds.size.height))
                cameraPreview.layer.addSublayer(previewLayer)
                cameraPreview.addGestureRecognizer(UITapGestureRecognizer(target: self, action:"saveToCamera:"))
//get instance of phone camera
    let captureDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
     //try to enable auto focus
     if(captureDevice!.isFocusModeSupported(.continuousAutoFocus)) {
         try! captureDevice!.lockForConfiguration()
         captureDevice!.focusMode = .continuousAutoFocus
         captureDevice!.unlockForConfiguration()
        view.addSubview(cameraPreview)

     }
  }
        }
    }
    func saveToCamera(sender: UITapGestureRecognizer) {
        if let videoConnection = stillImageOutput.connectionWithMediaType(AVMediaTypeVideo) {
            stillImageOutput.captureStillImageAsynchronouslyFromConnection(videoConnection) {
                (imageDataSampleBuffer, error) -> Void in
                let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageDataSampleBuffer)
                 UIImageWriteToSavedPhotosAlbum(UIImage(data: imageData), nil, nil, nil)
            }
        }
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}