android java CameraX调用系统相机

在 Android 中，使用 CameraX API 调用系统相机可以简化相机的集成和开发过程。以下是步骤：

1. 添加依赖项
在 app 的 build.gradle 文件中添加以下依赖项：

dependencies {
    def camerax_version = "1.0.0-beta12"

    // CameraX core library
    implementation "androidx.camera:camera-core:$camerax_version"
    // CameraX Camera2 extensions
    implementation "androidx.camera:camera-camera2:$camerax_version"
    // CameraX Lifecycle library
    implementation "androidx.camera:camera-lifecycle:$camerax_version"
    // CameraX View class
    implementation "androidx.camera:camera-view:1.0.0-alpha24"
}

2. 在布局文件中添加相机预览视图
在布局文件中添加一个 CameraView 视图，该视图将用于显示相机预览：

<androidx.camera.view.CameraView
    android:id="@+id/cameraView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

3. 创建相机实例
在 Activity 或 Fragment 中创建相机实例：

private lateinit var camera: Camera
private lateinit var cameraSelector: CameraSelector

private fun startCamera() {
    val cameraProviderFuture = ProcessCameraProvider.getInstance(this)

    cameraProviderFuture.addListener(Runnable {
        // Camera provider is now guaranteed to be available
        val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

        // Set up the preview use case
        val preview = Preview.Builder().build().also {
            it.setSurfaceProvider(cameraView.surfaceProvider)
        }

        // Set up the image capture use case
        val imageCapture = ImageCapture.Builder().build()

        // Set up the image analysis use case
        val imageAnalyzer = ImageAnalysis.Builder().build().also {
            it.setAnalyzer(cameraExecutor, LuminosityAnalyzer())
        }

        // Select the back camera as a default
        cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA

        // Set up the camera instance
        camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview, imageCapture, imageAnalyzer)
    }, ContextCompat.getMainExecutor(this))
}

4. 启动相机
在 onCreate() 方法中启动相机：

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    startCamera()
}

5. 拍照
实现拍照功能，可以在按钮点击事件中调用以下代码：

private fun takePhoto() {
    val imageCapture = imageCapture ?: return

    val photoFile = File(
        outputDirectory,
        SimpleDateFormat(FILENAME_FORMAT, Locale.US).format(System.currentTimeMillis()) + ".jpg"
    )

    val outputOptions = ImageCapture.OutputFileOptions.Builder(photoFile).build()

    imageCapture.takePicture(
        outputOptions,
        ContextCompat.getMainExecutor(this),
        object : ImageCapture.OnImageSavedCallback {
            override fun onImageSaved(outputFileResults: ImageCapture.OutputFileResults) {
                val savedUri = Uri.fromFile(photoFile)
                val msg = "Photo saved: $savedUri"
                Toast.makeText(baseContext, msg, Toast.LENGTH_SHORT).show()
            }

            override fun onError(exception: ImageCaptureException) {
                Log.e(TAG, "Photo capture failed: ${exception.message}", exception)
            }
        }
    )
}

以上是使用 CameraX API 调用系统相机的步骤。