How to pass image data of AVCaptureSession captured image to another view controller? - swift3

Question

I made a camera app using AVFoundation's AVCaptureSession and I wanted to pass the data of the captured image to another view controller.
This is the function where the capture os being handled:
func capturePhoto() {
self.counter += 1
if let videoConnection = sessionOutput.connection(withMediaType: AVMediaTypeVideo) {
videoConnection.videoOrientation = .landscapeRight
sessionOutput.captureStillImageAsynchronously(from: videoConnection, completionHandler: { (buffer, error) in
let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(buffer)
let data = NSData(data: imageData!)
// append the data to a global variable
DispatchQueue.main.async {
self.imageData?.append(data)
}
let image = UIImage(data: imageData!)!
UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
})
}
if self.counter == self.count {
self.timer?.invalidate()
self.timer = nil
self.counter = 0
self.shutterTimer.isHidden = true
self.shutterTimer.layer.removeAllAnimations()
// if the condition is met, then go to another vc with the image data
setupFrameAndSave()
}
}
this is the function that handles the segue to another view controller with the image data:
func setupFrameAndSave() {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let controller = storyboard.instantiateViewController(withIdentifier: "saveVC") as! SaveVC
controller.imageData = self.imageData
self.present(controller, animated: true, completion: nil)
}
Now, the problem is that the data that is being passed prints nil and placing the appending data to array inside DispatchQueue.main.async didn't do anything.