我正在使用CameraX，预览、图像和视频捕获。我创建了一个片段类，它使用绑定到生命周期来避免所有手动相机预览状态管理等（按照 Google 的建议）。问题是，有时如果我将应用程序置于后台然后置于前台，相机预览为黑色并且不显示预览。除了重新创建片段之外，没有其他方法可以恢复它。有什么提示我可能做错了什么吗？
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.util.Size;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.camera.core.AspectRatio;
import androidx.camera.core.Camera;
import androidx.camera.core.CameraSelector;
import androidx.camera.core.ImageAnalysis;
import androidx.camera.core.ImageCapture;
import androidx.camera.core.ImageCaptureException;
import androidx.camera.core.Preview;
import androidx.camera.core.UseCaseGroup;
import androidx.camera.core.VideoCapture;
import androidx.camera.lifecycle.ProcessCameraProvider;
import androidx.camera.view.PreviewView;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.mlkit.vision.face.Face;
import
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.util.List;
import java.util.Set;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
public class CameraViewFragment extends BaseFragment {
private static final int REQUEST_CAMERA_PERMISSIONS = 100;
private CameraViewFragmentListener listener;
private final Executor executor = Executors.newSingleThreadExecutor();
private Camera camera;
private Handler handler = new Handler();
private boolean isRecording;
private Preview preview;
private ImageCapture imageCapture;
private VideoCapture videoCapture;
private ImageAnalysis imageAnalysis;
private FaceDetector faceDetector;
public interface CameraViewFragmentListener {
void onCameraPictureTaken(byte[] buffer);
void onCameraPermissionsRejected();
void onCameraVideoRecorded(Uri file);
void onCameraVideoRecordError(Throwable ex);
void onCameraFacesDetect(List<Face> faces);
void onCameraFacesDetectError(Exception e);
enum CameraFeature {
PREVIEW,
IMAGE_CAPTURE,
VIDEO_CAPTURE,
FACE_DETECTION
}
Set<CameraFeature> cameraGetRequestedFeatures();
}
private FragmentCameraViewBinding binding;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
binding = FragmentCameraViewBinding.inflate(inflater, container, false);
return binding.getRoot();
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
int rc = ActivityCompat.checkSelfPermission(requireContext(), Manifest.permission.CAMERA);
if (rc == PackageManager.PERMISSION_GRANTED) {
startCamera();
} else {
requestCameraPermission();
}
}
private void requestCameraPermission() {
requestPermissions(new String[]{Manifest.permission.CAMERA}, REQUEST_CAMERA_PERMISSIONS);
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (requestCode == REQUEST_CAMERA_PERMISSIONS) {
if (permissions.length == 1 && permissions[0].equals(Manifest.permission.CAMERA) && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Logger.log(Logger.info, "[VRM] Camera permission granted.");
startCamera();//createCameraSource();
} else {
Logger.log(Logger.error, "[VRM] Camera permission NOT granted.");
if (listener != null) {
listener.onCameraPermissionsRejected();
}
requestCameraPermission();
}
}
}
/**
* Restarts the camera.
*/
@Override
public void onResume() {
super.onResume();
//startCamera();
}
/**
* Stops the camera.
*/
@Override
public void onPause() {
super.onPause();
}
/**
* Releases the resources associated with the camera source, the associated detector, and the
* rest of the processing pipeline.
*/
@Override
public void onDestroy() {
super.onDestroy();
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof CameraViewFragmentListener) {
listener = (CameraViewFragmentListener) context;
} else if (getParentFragment() instanceof CameraViewFragmentListener) {
listener = (CameraViewFragmentListener) getParentFragment();
}
}
@Override
public void onDetach() {
super.onDetach();
listener = null;
}
private void startCamera() {
final ListenableFuture<ProcessCameraProvider> cameraProviderFuture = ProcessCameraProvider.getInstance(requireContext());
cameraProviderFuture.addListener(() -> {
try {
ProcessCameraProvider cameraProvider = cameraProviderFuture.get();
Set<CameraViewFragmentListener.CameraFeature> features = listener.cameraGetRequestedFeatures();
bindUseCases(cameraProvider, features);
} catch (ExecutionException | InterruptedException e) {
// No errors need to be handled for this Future.
// This should never be reached.
Logger.log(Logger.error, "Exception while initializing CameraX: {}", e);
}
}, ContextCompat.getMainExecutor(requireContext()));
}
void bindUseCases(@NonNull ProcessCameraProvider cameraProvider, Set<CameraViewFragmentListener.CameraFeature> features) {
cameraProvider.unbindAll();
final CameraSelector cameraSelector = new CameraSelector.Builder()
.requireLensFacing(CameraSelector.LENS_FACING_FRONT)
.build();
final WindowManager wm = (WindowManager) requireContext().getSystemService(Context.WINDOW_SERVICE);
final UseCaseGroup.Builder useCaseGroupBuilder = new UseCaseGroup.Builder();
if (features.contains(CameraViewFragmentListener.CameraFeature.PREVIEW)) {
preview = new Preview.Builder()
.setTargetAspectRatio(AspectRatio.RATIO_4_3)
//.setTargetResolution(new Size(480, 640))
.build();
binding.preview.setScaleType(PreviewView.ScaleType.FILL_CENTER);
preview.setSurfaceProvider(binding.preview.getSurfaceProvider());
useCaseGroupBuilder.addUseCase(preview);
} else {
preview = null;
}
if (features.contains(CameraViewFragmentListener.CameraFeature.IMAGE_CAPTURE)) {
imageCapture = new ImageCapture.Builder()
.setCameraSelector(cameraSelector)
.setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)
//.setTargetAspectRatio(AspectRatio.RATIO_4_3)
.setTargetResolution(new Size(480, 640))
.setTargetRotation(wm.getDefaultDisplay().getRotation())
.build();
useCaseGroupBuilder.addUseCase(imageCapture);
} else {
imageCapture = null;
}
if (features.contains(CameraViewFragmentListener.CameraFeature.VIDEO_CAPTURE)) {
videoCapture = new VideoCapture.Builder()
.setCameraSelector(cameraSelector)
//.setTargetResolution(new Size(480, 640))
.setBitRate(1000)
.setTargetAspectRatio(AspectRatio.RATIO_4_3)
.setTargetRotation(wm.getDefaultDisplay().getRotation())
.build();
useCaseGroupBuilder.addUseCase(videoCapture);
} else {
videoCapture = null;
}
if (features.contains(CameraViewFragmentListener.CameraFeature.FACE_DETECTION)) {
imageAnalysis = new ImageAnalysis.Builder()
.setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
.build();
faceDetector = new FaceDetector(new FaceDetector.FaceDetectorListener() {
@Override
public void onFaceDetectSuccess(List<Face> faces) {
if (listener!=null)
listener.onCameraFacesDetect(faces);
}
@Override
public void onFaceDetectError(Exception e) {
if (listener!=null)
listener.onCameraFacesDetectError(e);
}
});
imageAnalysis.setAnalyzer(executor, faceDetector.createAnalyzer());
useCaseGroupBuilder.addUseCase(imageAnalysis);
} else {
imageAnalysis = null;
}
camera = cameraProvider.bindToLifecycle(this, cameraSelector, useCaseGroupBuilder.build());
}
public void requestTakePicture() {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ImageCapture.OutputFileOptions outputFileOptions = new ImageCapture.OutputFileOptions.Builder(bos).build();
imageCapture.takePicture(outputFileOptions, executor, new ImageCapture.OnImageSavedCallback() {
@Override
public void onImageSaved(@NonNull ImageCapture.OutputFileResults outputFileResults) {
handler.post(() -> {
//Toast.makeText(MainActivity.this, "Image Saved successfully", Toast.LENGTH_SHORT).show();
if (listener != null) {
listener.onCameraPictureTaken(bos.toByteArray());
}
});
}
@Override
public void onError(@NonNull ImageCaptureException error) {
error.printStackTrace();
}
});
}
public void startVideoRecording(File file) {
VideoCapture.OutputFileOptions outputFileOptions = new VideoCapture.OutputFileOptions
.Builder(file)
.build();
videoCapture.startRecording(outputFileOptions, executor, new VideoCapture.OnVideoSavedCallback() {
@Override
public void onVideoSaved(@NonNull VideoCapture.OutputFileResults outputFileResults) {
handler.post(() -> {
isRecording = false;
//Toast.makeText(MainActivity.this, "Image Saved successfully", Toast.LENGTH_SHORT).show();
if (listener != null) {
listener.onCameraVideoRecorded(outputFileResults.getSavedUri());
}
});
}
@Override
public void onError(int videoCaptureError, @NonNull String message, @Nullable Throwable cause) {
isRecording = false;
if (listener != null) {
listener.onCameraVideoRecordError(cause);
}
}
});
isRecording = true;
}
public void stopVideoRecording() {
videoCapture.stopRecording();
isRecording = false;
}
public boolean isRecording() {
return isRecording;
}
}
这里提出了一个问题： https://issuetracker.google.com/issues/147354615
使用建议的解决方案，您应该在 onResume() 中重新分配预览，例如：
private void setPreview() {
if (getLifecycle().getCurrentState() != Lifecycle.State.DESTROYED) {
Preview preview = new Preview.Builder().setTargetAspectRatio(AspectRatio.RATIO_4_3).build();
CameraSelector cameraSelector = new CameraSelector.Builder()
.requireLensFacing(CameraSelector.LENS_FACING_BACK).build();
preview.setSurfaceProvider(previewView.getSurfaceProvider());
cam = cameraProvider.bindToLifecycle(StockOCRFragment.this, cameraSelector, imageCapture, preview);
}
}
@Override
public void onPause() {
super.onPause();
stopped = true;
if (cameraProvider != null) {
cameraProvider.unbindAll();
}
}
@Override
public void onResume() {
super.onResume();
if (stopped && cameraProvider != null) {
setPreview();
}
}