Jetpack Compose中navigation-compose与CameraX搭配使用崩溃问题咨询

• 直接在Composable顶层执行cameraProviderFuture.get()：该方法为阻塞方法，会直接阻塞主线程，Future未完成时调用会抛出ExecutionException/InterruptedException，导航操作会触发NavHost页面重组，此时调用该方法大概率直接触发崩溃
• 相机核心实例（cameraProvider、imageCapture、camera、previewView）未使用remember包裹：Composable触发重组时这些实例会被重新初始化，导致点击拍照时持有的imageCapture为无效实例，甚至直接为空
• previewView直接在Composable顶层初始化：未和AndroidView的factory生命周期绑定，多次重组会创建多个PreviewView实例，和相机绑定的实例不一致
• 所用依赖均为早期alpha版本：navigation-compose 2.4.0-alpha09和camerax 1.1.0-alpha08本身存在大量已知生命周期适配、状态同步类bug

1. 相机核心实例加remember存储，避免重组丢失 #

@ExperimentalCoilApi
@Composable
fun CameraPreviewScreen(
    modifier: Modifier = Modifier,
    context: Context,
    lifecycleOwner: LifecycleOwner,
    outPutDirectory: File,
    onMediaCaptured: (Uri?) -> Unit
) {
    val cameraProviderFuture = remember { ProcessCameraProvider.getInstance(context) }
    val executor = remember { ContextCompat.getMainExecutor(context) }
    var imageCapture by remember { mutableStateOf<ImageCapture?>(null) }
    var camera by remember { mutableStateOf<Camera?>(null) }
    val previewView = remember { PreviewView(context) }
    val preview = remember { 
        Preview.Builder().build().also {
            it.setSurfaceProvider(previewView.surfaceProvider)
        } 
    }

    var lensFacing by remember { mutableStateOf(CameraSelector.LENS_FACING_BACK) }
    var flashEnabled by remember { mutableStateOf(false) }
    var flashRes by remember { mutableStateOf(R.drawable.ic_outlined_flash_on) }

2. 移除顶层阻塞的get调用，所有相机操作放到异步回调中 #

Box {
        AndroidView(
            factory = { ctx ->
                cameraProviderFuture.addListener(
                    {
                        // 仅在Future回调中调用get，避免阻塞主线程
                        val cameraProvider = cameraProviderFuture.get()
                        val cameraSelector = CameraSelector.Builder()
                            .requireLensFacing(lensFacing)
                            .build()
                        val newImageCapture = ImageCapture.Builder()
                            .setTargetRotation(previewView.display.rotation)
                            .build()
                        imageCapture = newImageCapture

                        try {
                            cameraProvider.unbindAll()
                            camera = cameraProvider.bindToLifecycle(
                                lifecycleOwner,
                                cameraSelector,
                                newImageCapture,
                                preview
                            )
                        } catch (e: Exception) {
                            Log.e("CameraX", "相机绑定失败", e)
                        }
                    }, executor
                )
                previewView
            },
            modifier = modifier
        )

3. 调整切换摄像头逻辑，避免操作未初始化的实例 #

// 底部切换摄像头按钮逻辑修改
        IconButton(
            onClick = {
                val newLensFacing = if (lensFacing == CameraSelector.LENS_FACING_BACK) CameraSelector.LENS_FACING_FRONT else CameraSelector.LENS_FACING_BACK
                lensFacing = newLensFacing
                cameraProviderFuture.addListener({
                    val cameraProvider = cameraProviderFuture.get()
                    val cameraSelector = CameraSelector.Builder()
                        .requireLensFacing(newLensFacing)
                        .build()
                    val currentImageCapture = imageCapture ?: return@addListener
                    try {
                        cameraProvider.unbindAll()
                        camera = cameraProvider.bindToLifecycle(
                            lifecycleOwner,
                            cameraSelector,
                            currentImageCapture,
                            preview
                        )
                    } catch (e: Exception) {
                        Log.e("CameraX", "切换摄像头失败", e)
                    }
                }, executor)
            }) {
            Icon(
                modifier = Modifier.size(34.dp),
                painter = painterResource(id = R.drawable.ic_outlined_rotate),
                contentDescription = null,
                tint = MaterialTheme.colors.surface
            )
        }

4. 拍照回调增加生命周期判断，避免页面销毁后触发导航 #

override fun onImageSaved(outputFileResults: ImageCapture.OutputFileResults) {
    Log.d(TAG, "image saved: ${photoFile.path}")
    // 仅页面处于活跃状态时触发回调导航
    if (lifecycleOwner.lifecycle.currentState.isAtLeast(Lifecycle.State.RESUMED)) {
        onMediaCaptured(Uri.fromFile(photoFile))
    }
}

5. 依赖版本升级 #

建议将依赖至少升级到正式稳定版，避免alpha版本自带bug：

• navigation-compose升级到2.4.1及以上稳定版
• camerax相关库升级到1.2.0及以上稳定版

内容的提问来源于stack exchange，提问作者Annon