如何使用相同的按钮启动和停止方法

Question

How would one go about starting and stopping this camera (or preview?) with the same onClick button? Starting the camera was no issue, but now also closing the camera, with the same button is proving to be more difficult for a newbie like me.

When pressing the button a second time, the program crashes now, which is not ideal.

public class MainActivity extends AppCompatActivity {

PreviewView previewView;
public int REQUEST_CODE_PERMISSIONS = 101;
public final String[] REQUIRED_PERMISSIONS = new String[]{"android.permission.CAMERA"};


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    previewView = findViewById(R.id.previewView);
    Button captureButton = findViewById(R.id.buttonPreview);
    captureButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
          if (allPermissionsGranted()) {
              startCamera();
          } else {
              ActivityCompat.requestPermissions(MainActivity.this, REQUIRED_PERMISSIONS, REQUEST_CODE_PERMISSIONS);
          }
      }
      });
}


@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull 
int[] grantResults) {
  super.onRequestPermissionsResult(requestCode, permissions, grantResults);
  if (allPermissionsGranted()) {
      startCamera();
  } else {
      Toast.makeText(this, "Permissions not granted by the user.", Toast.LENGTH_SHORT).show();
      finish();
  }
}

public boolean allPermissionsGranted() {

  for (String permission : REQUIRED_PERMISSIONS) {
      if (ContextCompat.checkSelfPermission(getApplicationContext(), permission) != PackageManager.PERMISSION_GRANTED) {
          return false;
      }
  }
  return true;
}
 public void startCamera() {
    ListenableFuture cameraProviderFuture = ProcessCameraProvider.getInstance(this);

    cameraProviderFuture.addListener(() -> {
        try {
            ProcessCameraProvider cameraProvider = (ProcessCameraProvider) cameraProviderFuture.get();
            Preview preview = new Preview.Builder().build();
            CameraSelector cameraSelector = new CameraSelector.Builder()
                    .requireLensFacing(CameraSelector.LENS_FACING_BACK)
                    .build();
            ImageAnalysis imageAnalysis =
                    new ImageAnalysis.Builder()
                            .setTargetResolution(new Size(1280, 720))
                            .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
                            .build();
            preview.setSurfaceProvider(previewView.getSurfaceProvider());
            Camera camera = cameraProvider.bindToLifecycle(
                    ((LifecycleOwner) this),
                    cameraSelector,
                    preview,
                    imageAnalysis);

        } catch (InterruptedException | ExecutionException e) {

        }
    }, ContextCompat.getMainExecutor(this));
}
}

Answer 1

Just need to create a boolean or int variable such as:

boolean ifCameraStarted=false;

When your called startCamera() you change this variable to true,and when you stopcamera change it to false; When you click the button,you judge with this variable if it is true or false and do different things