java - CameraX PreviewView 不显示任何内容

Question

我遵循了这些教程: https://developer.android.com/training/camerax/preview , https://proandroiddev.com/update-android-camerax-4a44c3e4cdcc我第一次运行应用程序时，预览工作正常，但在我旋转屏幕后，一切都坏了。我重新安装了应用程序，但预览不再起作用

public class ScanActivity extends AppCompatActivity {


private ListenableFuture<ProcessCameraProvider> cameraProviderFuture;

private PreviewView cameraView;
private Preview imagePreview;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_scan);
    cameraView = findViewById(R.id.cameraView);
    cameraProviderFuture = ProcessCameraProvider.getInstance(this);
    if(isPermissionsGranted()){
        cameraView.post(new Runnable() {
            @Override
            public void run() {
                startCamera();
            }
        });
    }
    else{
        ActivityCompat.requestPermissions(ScanActivity.this,
                new String[]{Manifest.permission.CAMERA},PERMISSION_REQUEST_CODE);
    }
}

private void startCamera(){
  imagePreview = new Preview.Builder()
           .setTargetRotation(cameraView.getDisplay().getRotation())
           .build();
  imagePreview.setSurfaceProvider(cameraView.getPreviewSurfaceProvider());
  final CameraSelector cameraSelector = new CameraSelector.Builder()
                            .requireLensFacing(CameraSelector.LENS_FACING_BACK)
                            .build();
  cameraProviderFuture.addListener(() -> {
      try {
          ProcessCameraProvider cameraProvider = cameraProviderFuture.get();
          cameraProvider.bindToLifecycle(ScanActivity.this,cameraSelector,imagePreview);
      } catch (ExecutionException|InterruptedException e) {
          e.printStackTrace();
      }
  },ContextCompat.getMainExecutor(this));

}

}

Answer 1

在相机初始化之前不应构建用例，这是 ProcessCameraProvider.getInstance() 异步执行的操作。因此，您可能会遇到的是在初始化完成之前构建预览用例，这就是预览不起作用的原因。您的代码应该如下所示。

cameraProviderFuture.addListener(() -> {
    try {
        ProcessCameraProvider cameraProvider = cameraProviderFuture.get(context);
        Preview preview = new Preview.Builder().build();
        preview.setSurfaceProvider(previewView.getSurfaceProvider());   
        cameraProvider.bindToLifecycle(lifecycleOwner, selector, preview);
    } catch (Exception exception) {
        exception.printStackTrace();
    }
}, ContextCompat.getMainExecutor(context));