背景

由于Jetpack Compose提升了开发效率和应用的性能，Jetpack Compose 已经被用在越来越多的应用中。CameraX相对于之前版本的相机库也有很大的性能提升，更加方便于调用和操作，下面我们简单的说一说如何在Compose中调用相机进行预览，并进行拍照。

1. 先简要的说明一下需要的相关依赖(Compose和CameraX)

implementation "androidx.compose.ui:ui:$compose_version"
implementation "androidx.compose.ui:ui-viewbinding:$compose_version"
implementation "androidx.compose.ui:ui-tooling-preview:$compose_version"
// The following line is optional, as the core library is included indirectly by camera-camera2
implementation "androidx.camera:camera-core:$camerax_version"
implementation "androidx.camera:camera-camera2:$camerax_version"
// If you want to additionally use the CameraX Lifecycle library
implementation "androidx.camera:camera-lifecycle:$camerax_version"
// If you want to additionally use the CameraX View class
implementation "androidx.camera:camera-view:$camerax_version"
// If you want to additionally use the CameraX Extensions library
implementation "androidx.camera:camera-extensions:$camerax_version"

2. 提供相机对象; 使用PreviewView提供相机预览；
   2.1. application中对CameraX配置

   class MyApplication : Application(), CameraXConfig.Provider {
   
        //这里标注只使用后摄像头，按需配置
        override fun getCameraXConfig(): CameraXConfig {
           return CameraXConfig.Builder.fromConfig(Camera2Config.defaultConfig())
           .setMinimumLoggingLevel(Log.ERROR)
           .setAvailableCamerasLimiter(CameraSelector.DEFAULT_BACK_CAMERA) 
           .build()
        }
   }
   

   2.2. 提供CameraX的相关扩展方法

   /**
      * 提供相机对象
       * @param onProvide 提供回调方法
       */
   fun Context.provideCameraProvider(onProvide: (ProcessCameraProvider?) -> Unit) {
       val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
       cameraProviderFuture.addListener({
           var processCameraProvider: ProcessCameraProvider? = null
           try {
               processCameraProvider = cameraProviderFuture.get()
           } catch (e: Exception) {
               HiLogger.singleton().printStackTrace(e)
           }
           onProvide.invoke(processCameraProvider)
       }, ContextCompat.getMainExecutor(this))
   }
   
   /** 拍照功能绑定到生命周期 **/
   @SuppressLint("RestrictedApi")
   fun PreviewView.imageCapture(
       owner: LifecycleOwner,
       provider: ProcessCameraProvider?
   ): ImageCapture {
       val viewPort = ViewPort.Builder(Rational(width, height), display.rotation).build()
       val preview = Preview.Builder()
           .setCameraSelector(CameraSelector.DEFAULT_BACK_CAMERA)
           .build()
           .also { it.setSurfaceProvider(surfaceProvider) }
       val cameraSelector = CameraSelector.Builder()
           .requireLensFacing(CameraSelector.LENS_FACING_BACK)
           .build()
       val imageCapture = ImageCapture.Builder()
           .setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)
           .build()
       val useCaseGroup = UseCaseGroup.Builder()
           .addUseCase(preview)
           .addUseCase(imageCapture)
           .setViewPort(viewPort)
           .build()
       provider?.unbindAll() //防止相机未解绑而发生闪退
       provider?.bindToLifecycle(owner, cameraSelector, useCaseGroup)
       return imageCapture
   }
   

   2.3. 提供Compose中使用的相机预览View

   /**
    * 相机预览视图
    * @param modifier 修饰器
    * @param cameraPictureFile 相机拍下来的图片
    * @param isPreviewEnable 是否开启预览
    * @param cameraProvider 相机提供对象
    * @param onStartPreview 开始预览
    * @param onTakePicture 拍照操作
    */
   @Composable
   @Preview(name = "效果预览", widthDp = 240, heightDp = 150)
   fun CameraPreviewView(
       modifier: Modifier = Modifier,
       cameraProvider: ProcessCameraProvider? = null,
       cameraPictureFile: File? = null,
       isPreviewEnable: Boolean = false,
       onStartPreview: () -> Unit = {},
       onTakePicture: (ImageCapture?) -> Unit = {},
   ) = Box(modifier.clip(ShunYunTongTheme.shapes.small)) {
       val localContext = LocalContext.current
       val lifecycleOwner = LocalLifecycleOwner.current
       val previewView = remember {
           PreviewView(localContext).apply {
               implementationMode = PreviewView.ImplementationMode.PERFORMANCE
           }
       }
       var cameraPreviewRunning by remember { mutableStateOf(false) }
       var imageCapture by remember { mutableStateOf<ImageCapture?>(null) }
       LaunchedEffect(isPreviewEnable, cameraProvider) {
           if (isPreviewEnable && cameraProvider != null) {
               try {
                   imageCapture =
                       previewView.imageCapture(lifecycleOwner, cameraProvider)
                   cameraPreviewRunning = true
               } catch (e: Exception) {
                   HiLogger.singleton().printStackTrace(e)
               }
           } else cameraPreviewRunning = false
       }
       AndroidView(
           modifier = Modifier
               .fillMaxSize()
               .background(Color.White),
           factory = { previewView })
       if (!isPreviewEnable) Image(
           modifier = Modifier
               .fillMaxSize()
               .click { onStartPreview() },
           contentDescription = null,
           contentScale = ContentScale.Crop,
           painter = imagePainter(cameraPictureFile ?: R.mipmap.ic_launcher),
       )
       Text(
           modifier = Modifier
               .align(Alignment.BottomCenter)
               .padding(bottom = dimensionResource(R.dimen.dp_12))
               .wrapContentSize()
               .clip(AppTheme.shapes.large)
               .background(Color.White)
               .border(1.dp, Color.LightGray, AppTheme.shapes.large)
               .click {
                   if (cameraProvider == null || !cameraPreviewRunning)
                       onStartPreview()
                   else onTakePicture(imageCapture)
               }
               .padding(
                   vertical = dimensionResource(R.dimen.dp_4),
                   horizontal = dimensionResource(R.dimen.dp_12),
               ),
           text = when {
               isPreviewEnable -> "点击拍照"
               else -> if (cameraPictureFile == null) "开启预览" else "重新拍照"
           },
           style = TextStyle(
               color = Color.Black,
               fontWeight = FontWeight.Bold,
               fontSize = fontDimensionResource(R.dimen.sp_15)
           )
       )
   }
   

   2.4. 调用示例

     class MyActivity : BaseActivity {
            private val viewModel by viewModels<MyViewModel>()
            override fun onCreate(savedInstanceState: Bundle?) {
               super.onCreate(savedInstanceState)
               setContent {
                   CameraPreviewView(
                       modifier = Modifier
                           .padding(dimensionResource(R.dimen.dp_16))
                           .fillMaxWidth()
                          .aspectRatio(16f / 9f)
                         .clip(AppTheme.shapes.small),
                      cameraProvider = cameraProvider,
                      isPreviewEnable = isPreviewEnable,
                      cameraPictureFile = cameraPictureFile,
                      onStartPreview = onStartPreview,
                      onTakePicture = onTakePicture
                  )
               }
               provideCameraProvider { provider ->
                   if (provider == null)
                   return@provideCameraProvider
                   viewModel.applyNewState { cameraProvider = provider }
               }
           }
      }
   

结尾

以上就是一个完整的调用示例了，拍照需要使用ImageCapture捕获照片，如下：

fun takePicture(
        context: Context,
        imageCapture: ImageCapture?,
        destImageFile: File,
        onStart: () -> Unit = {},
        onError: (Throwable) -> Unit = {},
        onSuccess: (File?) -> Unit,
    ) {
        onStart.invoke()
        if (imageCapture == null) {
            onError.invoke(Throwable("ImageCapture对象为空"))
            return
        }
        destImageFile.parentFile?.mkdirs()
        val executor = ContextCompat.getMainExecutor(context)
        val outputOptions = ImageCapture.OutputFileOptions
            .Builder(destImageFile)
            .build()
        val savedCallback = object : ImageCapture.OnImageSavedCallback {
            @SuppressLint("RestrictedApi")
            override fun onImageSaved(outputFileResults: ImageCapture.OutputFileResults) {
                onSuccess.invoke(outputOptions.file)
            }

            override fun onError(exception: ImageCaptureException) {
                onError.invoke(exception)
            }
        }
        imageCapture.takePicture(outputOptions, executor, savedCallback)
    }

*希望对初学者有所帮助，不懂的可以留言，如需转载请注明原文出处！