Kotlin“ surfaceChanged”，“ surfaceDestroyed”，SurfaceCreated“不会覆盖任何内容

如何解决Kotlin“ surfaceChanged”，“ surfaceDestroyed”，SurfaceCreated“不会覆盖任何内容

我正在片段中使用Surfaceview，但是surfaceHolder.Callback（surfaceCreated，surfaceChanged和surfaceDestroyed）的方法似乎没有覆盖任何内容。并且我还收到以下错误“对象不是抽象的，并且没有实现抽象成员“。

下面是图像中的错误。

e: /Users/malorimorow/AndroidStudioProjects/CapstoneProject/app/src/main/java/com/example/capstoneproject/main/ScannerFragment.kt: (158,32): Object is not abstract and does not implement abstract member public abstract fun surfaceChanged(p0: SurfaceHolder,p1: Int,p2: Int,p3: Int): Unit defined in android.view.SurfaceHolder.Callback

下面是源代码，您可以在overlay.apply方法中找到错误。我是kotlin的新手，非常感谢您的帮助。

class ScannerFragment : Fragment() {

    companion object {
        fun newInstance() = ScannerFragment()

        // We only need to analyze the part of the image that has text,so we set crop percentages
        // to avoid analyze the entire image from the live camera feed.
        const val DESIRED_WIDTH_CROP_PERCENT = 8
        const val DESIRED_HEIGHT_CROP_PERCENT = 74

        // This is an arbitrary number we are using to keep tab of the permission
        // request. Where an app has multiple context for requesting permission,// this can help differentiate the different contexts
        private const val REQUEST_CODE_PERMISSIONS = 10

        // This is an array of all the permission specified in the manifest
        private val REQUIRED_PERMISSIONS = arrayOf(Manifest.permission.CAMERA)
        private const val RATIO_4_3_VALUE = 4.0 / 3.0
        private const val RATIO_16_9_VALUE = 16.0 / 9.0
        private const val TAG = "ScannerFragment"
    }

    private var displayId: Int = -1
    private val viewModel: MainViewModel by viewModels()
    private var cameraProvider: ProcessCameraProvider? = null
    private var camera: Camera? = null
    private var imageAnalyzer: ImageAnalysis? = null
    private lateinit var container: ConstraintLayout
    private lateinit var viewFinder: PreviewView

    /** Blocking camera operations are performed using this executor */
    private lateinit var cameraExecutor: ExecutorService

    private lateinit var scopedExecutor: ScopedExecutor

    override fun onCreateView(
        inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?
    ): View {
        return inflater.inflate(R.layout.fragment_scanner,container,false)
    }

    override fun onDestroyView() {
        super.onDestroyView()

        // Shut down our background executor
        cameraExecutor.shutdown()
        scopedExecutor.shutdown()
    }

    override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
        super.onViewCreated(view,savedInstanceState)

        container = view as ConstraintLayout
        viewFinder = container.findViewById(R.id.viewfinder)

        // Initialize our background executor
        cameraExecutor = Executors.newSingleThreadExecutor()
        scopedExecutor = ScopedExecutor(cameraExecutor)

        // Request camera permissions
        if (allPermissionsGranted()) {
            // Wait for the views to be properly laid out
            viewFinder.post {
                // Keep track of the display in which this view is attached
                displayId = viewFinder.display.displayId

                // Set up the camera and its use cases
                setUpCamera()
            }
        } else {
            requestPermissions(
                REQUIRED_PERMISSIONS,REQUEST_CODE_PERMISSIONS
            )
        }

        // Get available language list and set up the target language spinner
        // with default selections.
        val adapter = ArrayAdapter(
            requireContext(),android.R.layout.simple_spinner_dropdown_item,viewModel.availableLanguages
        )

        targetLangSelector.adapter = adapter
        targetLangSelector.setSelection(adapter.getPosition(Language("en")))
        targetLangSelector.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
            override fun onItemSelected(
                parent: AdapterView<*>,view: View?,position: Int,id: Long
            ) {
                viewModel.targetLang.value = adapter.getItem(position)
            }

            override fun onNothingSelected(parent: AdapterView<*>) {}
        }

        viewModel.sourceLang.observe(viewLifecycleOwner,Observer { srcLang.text = it.displayName })
        viewModel.translatedText.observe(viewLifecycleOwner,Observer { resultOrError ->
            resultOrError?.let {
                if (it.error != null) {
                    translatedText.error = resultOrError.error?.localizedMessage
                } else {
                    translatedText.text = resultOrError.result
                }
            }
        })
        viewModel.modelDownloading.observe(viewLifecycleOwner,Observer { isDownloading ->
            progressBar.visibility = if (isDownloading) {
                View.VISIBLE
            } else {
                View.INVISIBLE
            }
            progressText.visibility = progressBar.visibility
        })

        overlay.apply {
            setZOrderOnTop(true)
            holder.setFormat(PixelFormat.TRANSPARENT)
            holder.addCallback(object : SurfaceHolder.Callback {
                override fun surfaceChanged(
                    holder: SurfaceHolder?,format: Int,width: Int,height: Int
                ) {
                }

                override fun surfaceDestroyed(holder: SurfaceHolder?) {
                }

                override fun surfaceCreated(holder: SurfaceHolder?) {
                    holder?.let { drawOverlay(it,DESIRED_HEIGHT_CROP_PERCENT,DESIRED_WIDTH_CROP_PERCENT
                    ) }
                }

            })
        }
    }


    /** Initialize CameraX,and prepare to bind the camera use cases  */
    private fun setUpCamera() {
        val cameraProviderFuture = ProcessCameraProvider.getInstance(requireContext())
        cameraProviderFuture.addListener(Runnable {

            // CameraProvider
            cameraProvider = cameraProviderFuture.get()

            // Build and bind the camera use cases
            bindCameraUseCases()
        },ContextCompat.getMainExecutor(requireContext()))
    }

    private fun bindCameraUseCases() {
        val cameraProvider = cameraProvider
            ?: throw IllegalStateException("Camera initialization failed.")

        // Get screen metrics used to setup camera for full screen resolution
        val metrics = DisplayMetrics().also { viewFinder.display.getRealMetrics(it) }
        Log.d(TAG,"Screen metrics: ${metrics.widthPixels} x ${metrics.heightPixels}")

        val screenAspectRatio = aspectRatio(metrics.widthPixels,metrics.heightPixels)
        Log.d(TAG,"Preview aspect ratio: $screenAspectRatio")

        val rotation = viewFinder.display.rotation

        val preview = Preview.Builder()
            .setTargetAspectRatio(screenAspectRatio)
            .setTargetRotation(rotation)
            .build()

        // Build the image analysis use case and instantiate our analyzer
        imageAnalyzer = ImageAnalysis.Builder()
            // We request aspect ratio but no resolution
            .setTargetAspectRatio(screenAspectRatio)
            .setTargetRotation(rotation)
            .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
            .build()
            .also {
                it.setAnalyzer(
                    cameraExecutor,TextAnalyzer(
                        requireContext(),lifecycle,viewModel.sourceText,viewModel.imageCropPercentages
                    )
                )
            }
        viewModel.sourceText.observe(viewLifecycleOwner,Observer { srcText.text = it })
        viewModel.imageCropPercentages.observe(viewLifecycleOwner,Observer { drawOverlay(overlay.holder,it.first,it.second) })

        // Select back camera since text detection does not work with front camera
        val cameraSelector =
            CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build()

        try {
            // Unbind use cases before rebinding
            cameraProvider.unbindAll()

            // Bind use cases to camera
            camera = cameraProvider.bindToLifecycle(
                this,cameraSelector,preview,imageAnalyzer
            )
            preview.setSurfaceProvider(viewFinder.createSurfaceProvider())
        } catch (exc: IllegalStateException) {
            Log.e(TAG,"Use case binding failed. This must be running on main thread.",exc)
        }
    }

    private fun drawOverlay(
        holder: SurfaceHolder,heightCropPercent: Int,widthCropPercent: Int
    ) {
        val canvas = holder.lockCanvas()
        val bgPaint = Paint().apply {
            alpha = 140
        }
        canvas.drawPaint(bgPaint)
        val rectPaint = Paint()
        rectPaint.xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)
        rectPaint.style = Paint.Style.FILL
        rectPaint.color = Color.WHITE
        val outlinePaint = Paint()
        outlinePaint.style = Paint.Style.STROKE
        outlinePaint.color = Color.WHITE
        outlinePaint.strokeWidth = 4f
        val surfaceWidth = holder.surfaceFrame.width()
        val surfaceHeight = holder.surfaceFrame.height()

        val cornerRadius = 25f
        // Set rect centered in frame
        val rectTop = surfaceHeight * heightCropPercent / 2 / 100f
        val rectLeft = surfaceWidth * widthCropPercent / 2 / 100f
        val rectRight = surfaceWidth * (1 - widthCropPercent / 2 / 100f)
        val rectBottom = surfaceHeight * (1 - heightCropPercent / 2 / 100f)
        val rect = RectF(rectLeft,rectTop,rectRight,rectBottom)
        canvas.drawRoundRect(
            rect,cornerRadius,rectPaint
        )
        canvas.drawRoundRect(
            rect,outlinePaint
        )
        val textPaint = Paint()
        textPaint.color = Color.WHITE
        textPaint.textSize = 50F

        val overlayText = getString(R.string.overlay_help)
        val textBounds = Rect()
        textPaint.getTextBounds(overlayText,overlayText.length,textBounds)
        val textX = (surfaceWidth - textBounds.width()) / 2f
        val textY = rectBottom + textBounds.height() + 15f // put text below rect and 15f padding
        canvas.drawText(getString(R.string.overlay_help),textX,textY,textPaint)
        holder.unlockCanvasAndPost(canvas)
    }

    /**
     *  [androidx.camera.core.ImageAnalysisConfig] requires enum value of
     *  [androidx.camera.core.AspectRatio]. Currently it has values of 4:3 & 16:9.
     *
     *  Detecting the most suitable ratio for dimensions provided in @params by comparing absolute
     *  of preview ratio to one of the provided values.
     *
     *  @param width - preview width
     *  @param height - preview height
     *  @return suitable aspect ratio
     */
    private fun aspectRatio(width: Int,height: Int): Int {
        val previewRatio = ln(max(width,height).toDouble() / min(width,height))
        if (abs(previewRatio - ln(RATIO_4_3_VALUE))
            <= abs(previewRatio - ln(RATIO_16_9_VALUE))
        ) {
            return AspectRatio.RATIO_4_3
        }
        return AspectRatio.RATIO_16_9
    }

    /**
     * Process result from permission request dialog box,has the request
     * been granted? If yes,start Camera. Otherwise display a toast
     */
    override fun onRequestPermissionsResult(
        requestCode: Int,permissions: Array<String>,grantResults: IntArray
    ) {
        if (requestCode == REQUEST_CODE_PERMISSIONS) {
            if (allPermissionsGranted()) {
                viewFinder.post {
                    // Keep track of the display in which this view is attached
                    displayId = viewFinder.display.displayId

                    // Set up the camera and its use cases
                    setUpCamera()
                }
            } else {
                Toast.makeText(
                    context,"Permissions not granted by the user.",Toast.LENGTH_SHORT
                ).show()
            }
        }
    }

    /**
     * Check if all permission specified in the manifest have been granted
     */
    private fun allPermissionsGranted() = REQUIRED_PERMISSIONS.all {
        ContextCompat.checkSelfPermission(
            requireContext(),it
        ) == PackageManager.PERMISSION_GRANTED
    }
}

解决方法

可能是因为版本冲突。只需删除所有3种方法并使用ALT+Enter来实现它们。再次。 如错误所述，surfaceChanged定义如下

fun surfaceChanged(p0: SurfaceHolder,p1: Int,p2: Int,p3: Int): Unit

但是在实现它时，您正在使SurfaceHolder参数为可空值。

holder.addCallback(object : SurfaceHolder.Callback {
            override fun surfaceChanged(
                holder: SurfaceHolder,format: Int,width: Int,height: Int
            ) {
            }

            override fun surfaceDestroyed(holder: SurfaceHolder) {
            }

            override fun surfaceCreated(holder: SurfaceHolder) {
                holder?.let { drawOverlay(it,DESIRED_HEIGHT_CROP_PERCENT,DESIRED_WIDTH_CROP_PERCENT
                ) }
            }

        })