【Android】CameraXで写真撮影

# はじめに
[以前の記事でCameraXの導入について解説](https://qiita.com/nakashimaakio/items/42cbaebca8d07ab09626)したが、CameraXでの写真撮影の方法について解説。

https://qiita.com/nakashimaakio/items/42cbaebca8d07ab09626

# ライブラリの導入
build.gradle(:app)に以下のライブラリを追加

```build.gradle
	implementation 'androidx.camera:camera-core:1.2.1'
	implementation 'androidx.camera:camera-camera2:1.2.1'
	implementation 'androidx.camera:camera-lifecycle:1.2.1'
	implementation 'androidx.camera:camera-view:1.2.1'
```

# カメラパーミッションの使用
マニフェストファイルにカメラを使用することを宣言。

```AndroidManifest.xml
<uses-permission android:name="android.permission.CAMERA"/>
```

# レイアウト作成
PreviewViewを使用してカメラ映像を表示。撮影用ボタンも追加。

```activity_main.xml
<androidx.constraintlayout.widget.ConstraintLayout
	xmlns:android="http://schemas.android.com/apk/res/android"
	xmlns:app="http://schemas.android.com/apk/res-auto"
	android:id="@+id/camera_container"
	android:layout_width="match_parent"
	android:layout_height="match_parent"
	android:background="@android:color/black">

	<androidx.camera.view.PreviewView
		android:id="@+id/view_finder"
		android:layout_width="0dp"
		android:layout_height="0dp"
		app:layout_constraintBottom_toBottomOf="parent"
		app:layout_constraintEnd_toEndOf="parent"
		app:layout_constraintStart_toStartOf="parent"
		app:layout_constraintTop_toTopOf="parent"/>

	<Button
		android:id="@+id/shutter_button"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:text="shutter"
		app:layout_constraintBottom_toBottomOf="parent"
		app:layout_constraintEnd_toEndOf="parent"
		app:layout_constraintStart_toStartOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
```

# 処理部分
`takePicture`メソッドで写真撮影処理を行っている。

```MainActivity.kt
class MainActivity : AppCompatActivity() {

	companion object {
		private const val REQUEST_CODE_PERMISSIONS = 10
		private val REQUIRED_PERMISSIONS = arrayOf(Manifest.permission.CAMERA)
	}

	private val binding by lazy { ActivityMainBinding.inflate(layoutInflater) }

	private val imageCapture: ImageCapture by lazy {
		ImageCapture.Builder().setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY).build()
	}

	override fun onCreate(savedInstanceState: Bundle?) {
		super.onCreate(savedInstanceState)
		setContentView(binding.root)

		if (allPermissionsGranted()) {
			startCamera()
		} else {
			ActivityCompat.requestPermissions(this, REQUIRED_PERMISSIONS, REQUEST_CODE_PERMISSIONS)
		}

		binding.shutterButton.setOnClickListener {
			takePicture()
		}
	}

	override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
		super.onRequestPermissionsResult(requestCode, permissions, grantResults)
		if (requestCode == REQUEST_CODE_PERMISSIONS) {
			if (allPermissionsGranted()) {
				startCamera()
			} else {
				Toast.makeText(this, "Permissions not granted by the user.", Toast.LENGTH_SHORT).show()
				finish()
			}
		}
	}

	private fun allPermissionsGranted() = REQUIRED_PERMISSIONS.all {
		ContextCompat.checkSelfPermission(baseContext, it) == PackageManager.PERMISSION_GRANTED
	}

	private fun startCamera() {
		val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
		cameraProviderFuture.addListener({ bindPreview(cameraProviderFuture.get()) }, ContextCompat.getMainExecutor(this))
	}

	private fun bindPreview(cameraProvider: ProcessCameraProvider) {
		val preview = Preview.Builder().build()
		val cameraSelector = CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build()
		preview.setSurfaceProvider(binding.viewFinder.surfaceProvider)
		cameraProvider.bindToLifecycle(this as LifecycleOwner, cameraSelector, preview, imageCapture)
	}

	private fun takePicture() {
		val contentValues = ContentValues()
		contentValues.put(MediaStore.MediaColumns.DISPLAY_NAME, SimpleDateFormat("yyyyMMddHHmmss").format(Date()) + ".jpg")
		contentValues.put(MediaStore.MediaColumns.MIME_TYPE, "image/jpeg")

		val outputFileOptions = ImageCapture.OutputFileOptions.Builder(contentResolver, MediaStore.Images.Media.EXTERNAL_CONTENT_URI, contentValues).build()

		imageCapture.takePicture(
			outputFileOptions,
			ContextCompat.getMainExecutor(this),
			object : ImageCapture.OnImageSavedCallback {
				override fun onImageSaved(outputFileResults: ImageCapture.OutputFileResults) {
					Toast.makeText(this@MainActivity, "success", Toast.LENGTH_LONG).show()
				}

				override fun onError(error: ImageCaptureException) {
					Toast.makeText(this@MainActivity, "error", Toast.LENGTH_LONG).show()
				}
			})
	}
}
```