CameraX的使用，面试学习

app:layout_constraintRight_toRightOf=“parent”

app:layout_constraintBottom_toBottomOf=“parent”

android:elevation=“2dp”

/>

<androidx.camera.view.PreviewView

android:id="@+id/viewFinder"

android:layout_width=“match_parent”

android:layout_height=“match_parent” />

第三步

在AndroidManifest.xml文件中申请权限

在第四步中要在activity的kt文件中添加请求权限的方法

第四步

创建mainactivity的kt文件，代码如下：

import androidx.appcompat.app.AppCompatActivity

import android.os.Bundle

import android.Manifest

import android.content.pm.PackageManager

import android.net.Uri

import android.util.Log

import android.widget.Toast

import androidx.core.app.ActivityCompat

import androidx.core.content.ContextCompat

import java.util.concurrent.Executors

import androidx.camera.core.*

import androidx.camera.lifecycle.ProcessCameraProvider

import kotlinx.android.synthetic.main.activity_main.*

import java.io.File

import java.nio.ByteBuffer

import java.text.SimpleDateFormat

import java.util.*

import java.util.concurrent.ExecutorService

typealias LumaListener = (luma: Double) -> Unit

class MainActivity : AppCompatActivity() {

private var imageCapture: ImageCapture? = null

private lateinit var outputDirectory: File

private lateinit var cameraExecutor: ExecutorService

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

setContentView(R.layout.activity_main)

// 请求相机权限

if (allPermissionsGranted()) {

startCamera()

} else {

ActivityCompat.requestPermissions(

this, REQUIRED_PERMISSIONS, REQUEST_CODE_PERMISSIONS)

}

// 设置拍照的监听按钮

camera_capture_button.setOnClickListener { takePhoto() }

outputDirectory = getOutputDirectory()

cameraExecutor = Executors.newSingleThreadExecutor()

}

private fun takePhoto() {

// 获得可修改的图像捕获用例

val imageCapture = imageCapture ?: return

// 创建带时间戳的输出文件用于保存文件

val photoFile = File(

outputDirectory,

SimpleDateFormat(FILENAME_FORMAT, Locale.US

).format(System.currentTimeMillis()) + “.jpg”)

// 创建输出选项对象

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

// 设置图像捕获监听器，拍照后触发

imageCapture.takePicture(

outputOptions, ContextCompat.getMainExecutor(this), object : ImageCapture.OnImageSavedCallback {

override fun onError(exc: ImageCaptureException) {

Log.e(TAG, “Photo capture failed: ${exc.message}”, exc)

}

override fun onImageSaved(output: ImageCapture.OutputFileResults) {

val sa

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vedUri = Uri.fromFile(photoFile)

val msg = “Photo capture succeeded: $savedUri”

Toast.makeText(baseContext, msg, Toast.LENGTH_SHORT).show()

Log.d(TAG, msg)

}

})

}

private fun startCamera() {

val cameraProviderFuture = ProcessCameraProvider.getInstance(this)

cameraProviderFuture.addListener(Runnable {

// 用于将摄像机的生命周期绑定到生命周期所有者

val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

val preview = Preview.Builder()

.build()

.also {

it.setSurfaceProvider(viewFinder.createSurfaceProvider())

}

imageCapture = ImageCapture.Builder()

.build()

// 默认选择后置摄像头，这边可以设置方法选择摄像头

val cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA

try {

cameraProvider.unbindAll()

// 将用例绑定到相机

cameraProvider.bindToLifecycle(

this, cameraSelector, preview, imageCapture)

} catch(exc: Exception) {

Log.e(TAG, “Use case binding failed”, exc)

}

}, ContextCompat.getMainExecutor(this))

}

private fun allPermissionsGranted() = REQUIRED_PERMISSIONS.all {

ContextCompat.checkSelfPermission(

baseContext, it) == PackageManager.PERMISSION_GRANTED

}

//申请权限的方法

override fun onRequestPermissionsResult(

requestCode: Int, permissions: Array, grantResults:

IntArray) {

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 getOutputDirectory(): File {

val mediaDir = externalMediaDirs.firstOrNull()?.let {

File(it, resources.getString(R.string.app_name)).apply { mkdirs() } }

return if (mediaDir != null && mediaDir.exists())

mediaDir else filesDir

}

override fun onDestroy() {

super.onDestroy()

cameraExecutor.shutdown()

}

companion object {

private const val TAG = “CameraXBasic”

private const val FILENAME_FORMAT = “yyyy-MM-dd-HH-mm-ss-SSS”

private const val REQUEST_CODE_PERMISSIONS = 10

private val REQUIRED_PERMISSIONS = arrayOf(Manifest.permission.CAMERA)

}

}

到此就可以利用CameraX实现一个可拍照储存的相机

CameraX的进阶使用

=======================================================================

CameraX可以和MLKit或Tensorflow Lite一起使用，来对图像进行实施分析。

如果要使用Tensorflow Lite，首先要在build.gradle(module:app)添加Tensorflow Lite的依赖，并进行gradle同步。

implementation ‘org.tensorflow:tensorflow-lite:0.0.0-nightly’

implementation ‘org.tensorflow:tensorflow-lite-gpu:0.0.0-nightly’

implementation ‘org.tensorflow:tensorflow-lite-support:0.0.0-nightly’

然后在ImageAnalysis.Analyzer接口的类中重写函数。

imageAnalysis.setAnalyzer(executor, ImageAnalysis.Analyzer { image ->

if (!::bitmapBuffer.isInitialized) {