我正在制作QR扫描仪。当所有代码都写在ViewController内的某个地方时，我的代码可以工作，但是当我对其进行模块化时，就不会在AVCaptureMetadataOutputObjectsDelegate内得到回调。
import Foundation
import UIKit
import AVFoundation
class CameraSource : NSObject {
private var session : AVCaptureSession?
private var inputDevice : AVCaptureDeviceInput?
private var videoPreviewLayer : AVCaptureVideoPreviewLayer?
private var captureMetadataOutput : AVCaptureMetadataOutput?
func setCaptureMetadataOutput() {
self.captureMetadataOutput = nil
self.captureMetadataOutput = AVCaptureMetadataOutput()
}
func getCaptureMetadataOutput() -> AVCaptureMetadataOutput? {
return self.captureMetadataOutput
}
func setInputDevice(inputDevice : AVCaptureDeviceInput?) {
self.inputDevice = inputDevice
}
func getInputDevice() -> AVCaptureDeviceInput? {
return self.inputDevice
}
func setSession(session : AVCaptureSession?) {
self.session = session
}
func getSession() -> AVCaptureSession? {
return self.session
}
func setMetadataObjects(metaObjects : [AVMetadataObject.ObjectType], delegate : AVCaptureMetadataOutputObjectsDelegate) {
assert(self.captureMetadataOutput != nil)
self.captureMetadataOutput!.setMetadataObjectsDelegate(delegate, queue: DispatchQueue.main)
self.captureMetadataOutput!.metadataObjectTypes = metaObjects
}
func initViewoPreviewLayer(videoGravity : AVLayerVideoGravity, orientation : AVCaptureVideoOrientation) {
assert(session != nil)
videoPreviewLayer = AVCaptureVideoPreviewLayer(session: session!)
videoPreviewLayer!.videoGravity = videoGravity
videoPreviewLayer!.connection!.videoOrientation = orientation
}
func addVideoLayerToImageView(imageView : UIImageView) {
assert(self.videoPreviewLayer != nil)
imageView.layer.addSublayer(self.videoPreviewLayer!)
self.videoPreviewLayer!.frame = imageView.bounds
}
func startSession() {
assert(session != nil)
self.session!.startRunning()
}
/*==========================================================================
STATIC FUNCTIONS
==========================================================================*/
static func getBackCamera() -> AVCaptureDevice {
return AVCaptureDevice.default(.builtInWideAngleCamera, for: AVMediaType.video, position: .back)!
}
static func getFrontCamera() -> AVCaptureDevice {
return AVCaptureDevice.default(.builtInWideAngleCamera, for: AVMediaType.video, position: .front)!
}
static func isCameraAvailable() -> Bool {
if #available(iOS 10.0, *) {
let count : Int = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera],
mediaType: AVMediaType.video,
position: .unspecified).devices.count
if count > 0 { return true }
}
else {
let count = AVCaptureDevice.devices(for: AVMediaType.video).count
if count > 0 { return true }
}
return false
}
/*==========================================================================
CAMERA BUILDER CLASS
==========================================================================*/
class Builder {
var cameraSource : CameraSource
init() {
cameraSource = CameraSource()
}
func createSession() -> Builder {
if (cameraSource.getSession() != nil) {
cameraSource.setSession(session: nil)
}
cameraSource.setSession(session: AVCaptureSession())
return self
}
func setSessionPreset(preset : AVCaptureSession.Preset) -> Builder {
assert(cameraSource.getSession() != nil)
cameraSource.getSession()!.sessionPreset = preset
return self
}
func attachInputDevice(camera : AVCaptureDevice) throws -> Builder {
try self.prepareInputDevice(camera: camera)
try self.addInputToSession()
assert(cameraSource.inputDevice != nil)
return self
}
func addOutputToSessionForMetaData() throws -> CameraSource {
cameraSource.setCaptureMetadataOutput()
assert(cameraSource.getSession() != nil && cameraSource.getCaptureMetadataOutput() != nil)
if !cameraSource.getSession()!.canAddOutput(cameraSource.getCaptureMetadataOutput()!) {
throw AppErrorCode.cameraError("Unable to attach output to camera session")
}
cameraSource.getSession()!.addOutput(cameraSource.getCaptureMetadataOutput()!)
return self.cameraSource
}
/*==========================================================================
BUILDER PRIVATE FUNCTIONS
==========================================================================*/
private func prepareInputDevice(camera : AVCaptureDevice) throws {
do {
let inputDevice = try AVCaptureDeviceInput(device: camera)
cameraSource.setInputDevice(inputDevice: inputDevice)
} catch let error as NSError {
print(error.localizedDescription)
throw AppErrorCode.cameraError("Unable to attach input to camera session")
}
}
private func addInputToSession() throws {
if(cameraSource.getSession() == nil) {
throw AppErrorCode.cameraError("Unable to create camera session")
}
assert(cameraSource.getInputDevice() != nil && cameraSource.getSession()!.canAddInput(cameraSource.getInputDevice()!))
cameraSource.getSession()!.addInput(cameraSource.getInputDevice()!)
}
}
}
我的QR扫描仪代码看起来像
import UIKit
import Foundation
import AVFoundation
protocol QRScannerDelegate {
func scannedData(_ scannedString : String)
}
class QRScanner : NSObject {
private var cameraSource : CameraSource?
var delegate : QRScannerDelegate?
func prepareCamera (delegate : QRScannerDelegate) throws -> QRScanner {
do {
self.delegate = delegate
self.cameraSource = try CameraSource
.Builder()
.createSession()
.setSessionPreset(preset: .photo)
.attachInputDevice(camera: CameraSource.getBackCamera())
.addOutputToSessionForMetaData()
self.cameraSource!.setMetadataObjects(metaObjects: [.qr], delegate: self as AVCaptureMetadataOutputObjectsDelegate)
} catch let err as NSError {
print(err.localizedDescription)
self.cameraSource = nil
throw AppErrorCode.cameraError("Unable to process camera with one or more issue")
}
return self
}
func initViewoPreviewLayer(videoGravity : AVLayerVideoGravity, orientation : AVCaptureVideoOrientation) -> QRScanner{
assert(cameraSource != nil)
self.cameraSource!.initViewoPreviewLayer(videoGravity: videoGravity, orientation: orientation)
return self
}
func addVideoLayerToImageView(imageView : UIImageView) -> QRScanner{
assert(cameraSource != nil)
self.cameraSource!.addVideoLayerToImageView(imageView: imageView)
return self
}
func startSession() {
assert(cameraSource != nil)
self.cameraSource!.startSession()
}
}
extension QRScanner : AVCaptureMetadataOutputObjectsDelegate {
func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
print("Delegate called")
if metadataObjects.count == 0 {
self.delegate?.scannedData("No Data")
} else {
let metadataObj = metadataObjects[0] as! AVMetadataMachineReadableCodeObject
if metadataObj.type == AVMetadataObject.ObjectType.qr {
if metadataObj.stringValue != nil {
print("Scanner Getting data: \(metadataObj.stringValue!)")
self.delegate?.scannedData(metadataObj.stringValue!)
}
}
}
}
}
我在QRScannerDelegate中实现了ViewController，但是我什么也没得到。而且我什至没有在AVCaptureMetadataOutputObjectsDelegate内部获得回调。
我尝试将ViewController实例作为AVCaptureMetadataOutputObjectsDelegate传递，然后我获得了扫描信息的回调。
所以我的问题是为什么会这样？
1）当我以AVCaptureMetadataOutputObjectsDelegate的身份传递普通课程时，我没有得到回调。但是。
2）当我将UIViewController实例作为AVCaptureMetadataOutputObjectsDelegate传递时，我能够获得回调。
更新
这就是我从View Controller呼叫prepareCamera的方式
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
do {
try QRScanner().prepareCamera(delegate: self)
.initViewoPreviewLayer(videoGravity: .resizeAspectFill, orientation: .portrait)
.addVideoLayerToImageView(imageView: self.qrScannerImageView)
.startSession()
} catch {
print("Some Camera Error")
}
self.createOverlay()
}
答案 0 :(得分：1)
在不知道您如何呼叫prepareCamera的情况下很难确定，因为这是触发setMetadataObjectsDelegate的原因，但是对我来说，您似乎并没有在其中强烈引用QRScanner您的ViewController（将其实例化为实例变量）可以解释为什么当ViewController是您的AVCaptureMetadataOutputObjectsDelegate时，由于ViewController仍在内存中，因此回调被击中了。
还值得注意的是，如果ViewController是您的QRScannerDelegate，则需要将委托定义为weak var delegate : QRScannerDelegate?，以防止内存泄漏。
编辑： 更改
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
do {
try QRScanner().prepareCamera(delegate: self)
.initViewoPreviewLayer(videoGravity: .resizeAspectFill, orientation: .portrait)
.addVideoLayerToImageView(imageView: self.qrScannerImageView)
.startSession()
} catch {
print("Some Camera Error")
}
self.createOverlay()
}
到
var qrScanner = QRScanner()
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
do {
try self.qrScanner.prepareCamera(delegate: self)
.initViewoPreviewLayer(videoGravity: .resizeAspectFill, orientation: .portrait)
.addVideoLayerToImageView(imageView: self.qrScannerImageView)
.startSession()
} catch {
print("Some Camera Error")
}
self.createOverlay()
}
并更改
protocol QRScannerDelegate {
func scannedData(_ scannedString : String)
}
到
protocol QRScannerDelegate: class {
func scannedData(_ scannedString : String)
}
允许弱势代表
AVCaptureMetadataOutputObjectsDelegate很难，但是您可以用它做一些非常酷的事情！所以继续吧。
我拉出了我之前写的一些QRScanner代码，如果要查看，请把它放进去。它比您拥有的要精简得多，但是您可能会发现它很有帮助。 https://gist.github.com/aChase55/733ea89af1bfa80c65971d3bc691f0b2