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
java
/** 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.
*/
@ExperimentalLensFacing
public 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
java
private ListenableFuture<ProcessCameraProvider> 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
java
<?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">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="vertical">
<androidx.camera.view.PreviewView
android:id="@+id/previewView"
android:layout_width="300dp"
android:layout_height="300dp"
android:layout_gravity="center"
/>
<Button
android:id="@+id/take_photo"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:text="取图"/>
<ImageView
android: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）
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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