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Android相机调用有原生的Camera和Camera2，我觉得调用代码都太复杂了，CameraX调用代码简洁很多。

说明文档：https://developer.android.com/jetpack/androidx/releases/camera?hl=zh-cn

现有查到的调用资料都不够新，对于外接摄像头（USB摄像头）这类非前置也非后置摄像头的设备调用，都说是没有实现。旧版本的库可能更多目标用户是基于手机的，1.3.0-alpha03版本针对外接摄像头有增加配置项（CameraSelector.LENS_FACING_EXTERNAL），使用该配置项可以实现外接摄像头的调用。

0，摄像头选择可用值

    /** A camera on the devices that its lens facing is resolved. */public static final int LENS_FACING_UNKNOWN = -1;/** A camera on the device facing the same direction as the device's screen. */public static final int LENS_FACING_FRONT = 0;/** A camera on the device facing the opposite direction as the device's screen. */public static final int LENS_FACING_BACK = 1;/*** An external camera that has no fixed facing relative to the device's screen.** <p>The behavior of an external camera highly depends on the manufacturer. Currently it's* treated similar to a front facing camera with little verification. So it's considered* experimental and should be used with caution.*/@ExperimentalLensFacingpublic static final int LENS_FACING_EXTERNAL = 2;

1，在AndroidManifest.xml添加权限

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

2，在settings.gradle或build.gradle添加maven

    repositories {google()mavenCentral()maven { url 'https://jitpack.io' }}

3，在build.gradle添加依赖库

    //摄像头预览库implementation "androidx.camera:camera-core:1.3.0-alpha04"// CameraX Camera2 extensions[可选]拓展库可实现人像、HDR、夜间和美颜、滤镜但依赖于OEMimplementation "androidx.camera:camera-camera2:1.3.0-alpha04"// CameraX Lifecycle library[可选]避免手动在生命周期释放和销毁数据implementation "androidx.camera:camera-lifecycle:1.3.0-alpha04"// CameraX View class[可选]最佳实践，最好用里面的PreviewView，它会自行判断用SurfaceView还是TextureView来实现implementation 'androidx.camera:camera-view:1.3.0-alpha04'

4，开启预览代码

    private ListenableFuture<ProcessCameraProvider> cameraProviderFuture;private PreviewView previewView;private ProcessCameraProvider cameraProvider;ImageView picture = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);picture = (ImageView) findViewById(R.id.picture);previewView=findViewById(R.id.previewView);//初始化//高版本系统动态权限申请if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_DENIED) {if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {requestPermissions(new String[]{Manifest.permission.CAMERA,}, 11);}} else {//启动相机startCamera();}takePhoto.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View view) {takePhoto(picture);//取图识别}});}@Overridepublic void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {super.onRequestPermissionsResult(requestCode, permissions, grantResults);if (requestCode==11){//获取权限后，开启摄像头//启动相机startCamera();}}private void startCamera() {// 请求 CameraProvidercameraProviderFuture = ProcessCameraProvider.getInstance(this);//检查 CameraProvider 可用性，验证它能否在视图创建后成功初始化cameraProviderFuture.addListener(() -> {try {ProcessCameraProvider cameraProvider = cameraProviderFuture.get();bindPreview(cameraProvider);} catch (ExecutionException | InterruptedException e) {// No errors need to be handled for this Future.// This should never be reached.}}, ContextCompat.getMainExecutor(this));}//选择相机并绑定生命周期和用例private void bindPreview(@NonNull ProcessCameraProvider cp) {this.cameraProvider=cp;Preview preview = new Preview.Builder().build();@SuppressLint("UnsafeOptInUsageError")CameraSelector cameraSelector = new CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK)//CameraSelector.LENS_FACING_EXTERNAL.build();preview.setSurfaceProvider(previewView.getSurfaceProvider());cameraProvider.unbindAll();//解绑组件cameraProvider.bindToLifecycle((LifecycleOwner) this, cameraSelector, preview);}//拍照，这里偷懒了，直接取了预览控件的图片，需要拍照的再去看看官方文档吧public void takePhoto(View view){Log.e("OCR", "takePhoto");Bitmap bitmap = previewView.getBitmap();view.setBackground(new BitmapDrawable(getApplicationContext().getResources(),bitmap)); //show picture}@Overrideprotected void onDestroy() {super.onDestroy();cameraProvider.unbindAll();}

5，界面布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:layout_margin="5dp"android:orientation="vertical"><androidx.camera.view.PreviewViewandroid:id="@+id/previewView"android:layout_width="300dp"android:layout_height="300dp"android:layout_gravity="center"/><Buttonandroid:id="@+id/take_photo"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_margin="5dp"android:text="取图"/><ImageViewandroid:id="@+id/picture"android:layout_width="300dp"android:layout_height="300dp"android:layout_gravity="center"/></LinearLayout></androidx.coordinatorlayout.widget.CoordinatorLayout>

6，测试效果（文字识别部分请忽略）

7，库的调用版本是比较新的，建议JDK版本不要太低，我使用的是16.0.2

新人入行，经验分享，如有所误，欢迎指出~

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