自定义相机需要很长时间来保存图像(Swift 和 AVFoundation)

Question

我下面的代码是一个有效的自定义相机。我的目标是在这里拍照并将其调整为正方形。之后，我将图像分配给UIImage，并通过segue传递给后期控制器。在图像本身保存之前，Segue 最终会发生。我知道这一点，因为 segue 会发生，几秒钟后控制台将打印 UIImage 的值。

class CameraViewController: UIViewController {

@IBOutlet weak var photoButton: UIButton!
@IBOutlet weak var previewView: UIView!

var captureSession: AVCaptureSession?
var stillImageOutput: AVCaptureStillImageOutput?
var previewLayer: AVCaptureVideoPreviewLayer?
var buttonImage = UIImage(named: "CameraButton.png")
var captImage = UIImage()
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}
override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    photoButton.setBackgroundImage(buttonImage, forState: .Normal)
    captureSession = AVCaptureSession()
    captureSession!.sessionPreset = AVCaptureSessionPresetPhoto
    let backCamera = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    var error: NSError?
    var input: AVCaptureDeviceInput!
    do {
        input = try AVCaptureDeviceInput(device: backCamera)
    } catch let error1 as NSError {
        error = error1
        input = nil
    }
    if error == nil && captureSession!.canAddInput(input) {
        captureSession!.addInput(input)
        stillImageOutput = AVCaptureStillImageOutput()
        stillImageOutput!.outputSettings = [AVVideoCodecKey: AVVideoCodecJPEG]
        if captureSession!.canAddOutput(stillImageOutput) {
            captureSession!.addOutput(stillImageOutput)
            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            previewLayer!.videoGravity = AVLayerVideoGravityResizeAspectFill
            previewLayer!.connection?.videoOrientation = AVCaptureVideoOrientation.Portrait
            previewView.layer.addSublayer(previewLayer!)
            captureSession!.startRunning()
        }
    }
}
override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    previewLayer!.frame = previewView.bounds
}
@IBAction func didPressTakePhoto(sender: UIButton) {
    if let videoConnection = stillImageOutput!.connectionWithMediaType(AVMediaTypeVideo) {
        videoConnection.videoOrientation = AVCaptureVideoOrientation.Portrait
        stillImageOutput?.captureStillImageAsynchronouslyFromConnection(videoConnection, completionHandler: {(sampleBuffer, error) in
            if (sampleBuffer != nil) {
                let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(sampleBuffer)
                let dataProvider = CGDataProviderCreateWithCFData(imageData)
                let cgImageRef = CGImageCreateWithJPEGDataProvider(dataProvider, nil, true, CGColorRenderingIntent.RenderingIntentDefault)
                var image = UIImage(CGImage: cgImageRef!, scale: 1.0, orientation: UIImageOrientation.Right)
                //Crop the image to a square
                let imageSize: CGSize = image.size
                let width: CGFloat = imageSize.width
                let height: CGFloat = imageSize.height
                if width != height {
                    let newDimension: CGFloat = min(width, height)
                    let widthOffset: CGFloat = (width - newDimension) / 2
                    let heightOffset: CGFloat = (height - newDimension) / 2
                    UIGraphicsBeginImageContextWithOptions(CGSizeMake(newDimension, newDimension), false, 0.0)
                    image.drawAtPoint(CGPointMake(-widthOffset, -heightOffset), blendMode: .Copy, alpha: 1.0)
                    image = UIGraphicsGetImageFromCurrentImageContext()
                    UIGraphicsEndImageContext()
                    self.captImage = image
                    print(self.captImage)
                }
            }
        })
        self.performSegueWithIdentifier("fromCustomCamera", sender: self)
    }

}
@IBAction func didPressTakeAnother(sender: AnyObject) {
    captureSession!.startRunning()
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "fromCustomCamera"{
        let svc = segue.destinationViewController as! PostViewController
        svc.imageRec = self.captImage
    }
}
}

Answer 1

如果要确保在调用完成后执行，则必须在异步函数的完成处理程序中调用performSegueWithIdentifier