def camerax_version = "1.0.0"
// CameraX core library using camera2 implementation
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"

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             android:layout_width="match_parent"
             android:layout_height="match_parent">

    <androidx.camera.view.PreviewView
        android:id="@+id/viewFinder"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    
</FrameLayout>

manifest中添加：
<uses-feature android:name="android.hardware.camera.any" />
    <uses-permission android:name="android.permission.CAMERA" />


fragment或activity中使用registerforactivityresult

import androidx.camera.lifecycle.ProcessCameraProvider
import com.google.common.util.concurrent.ListenableFuture

class MainActivity : AppCompatActivity() {
    private lateinit var cameraProviderFuture : ListenableFuture<ProcessCameraProvider>//定义一个字段
    override fun onCreate(savedInstanceState: Bundle?) {
     startCamera()
    }

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

 private fun startCamera() {
       cameraProviderFuture = ProcessCameraProvider.getInstance(requireContext())//创建 ProcessCameraProvider 的实例。这用于将相机的生命周期绑定到生命周期所有者。这消除了打开和关闭相机的任务，因为 CameraX 具有生命周期感知能力。

        cameraProviderFuture.addListener(Runnable {//----------1
            val cameraProvider = cameraProviderFuture.get()//用来把相机的生命周期绑定到fragment
            bindPreview(cameraProvider)
        }, ContextCompat.getMainExecutor(requireContext()))
    }

    private fun bindPreview(cameraProvider : ProcessCameraProvider) {
        val preview : Preview = Preview.Builder()//构建preview-----------------2
            .build().also {
                it.setSurfaceProvider(previewView.surfaceProvider)//和androidx.camera.view.PreviewView控件绑定
            }

        val cameraSelector : CameraSelector = CameraSelector.Builder()//选择前后相机----------------3
            .requireLensFacing(CameraSelector.LENS_FACING_BACK)//可选择前相机或后相机
            .build()


        var camera = cameraProvider.bindToLifecycle(this as LifecycleOwner, cameraSelector, preview)//把相机的生命周期绑定到fragment---------4
                                                                                                    //目前只有preview这一个usecase
    }