Android相机调用-CameraX【外接摄像头】【USB摄像头】

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.
     *
     * 
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.
     */
    @ExperimentalLensFacing
    public static final int LENS_FACING_EXTERNAL = 2;

1，在AndroidManifest.xml添加权限

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OEM
    implementation "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 cameraProviderFuture;
    private PreviewView previewView;
    private ProcessCameraProvider cameraProvider;
    ImageView picture = null;

    @Override
    protected 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() {
            @Override
            public void onClick(View view) {
                takePhoto(picture);//取图识别
            }
        });
    }

    @Override
    public 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 CameraProvider
        cameraProviderFuture = 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

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraProvider.unbindAll();
    }

    

5，界面布局

6，测试效果（文字识别部分请忽略）

s

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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