我知道这个问题已被多次询问，但我没有其他选择，只能再次提出这个问题。我正在使用camera2 api在同一屏幕上显示前后摄像头。我创建了两个纹理视图，每个视图都有两个相机实例。即使这样，我也会遇到异常。
这是我的MainActivity.java代码：
public class MainActivity extends AppCompatActivity {
private static final String TAG = "AndroidCameraApi";
private TextureView textureView,textureView1;
private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
static {
ORIENTATIONS.append(Surface.ROTATION_0, 90);
ORIENTATIONS.append(Surface.ROTATION_90, 0);
ORIENTATIONS.append(Surface.ROTATION_180, 270);
ORIENTATIONS.append(Surface.ROTATION_270, 180);
}
private String cameraId,cameraId1;
protected CameraDevice cameraDevice,cameraDevice1;
protected CameraCaptureSession cameraCaptureSessions,cameraCaptureSessions1;
protected CaptureRequest.Builder captureRequestBuilder,captureRequestBuilder1;
private Size imageDimension,imageDimension1;
private static final int REQUEST_CAMERA_PERMISSION = 200;
private Handler mBackgroundHandler,mBackgroundHandler1;
private HandlerThread mBackgroundThread,mBackgroundThread1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_android_camera_api);
textureView = (TextureView) findViewById(R.id.texture);
textureView1 = (TextureView) findViewById(texture1);
assert textureView != null;
assert textureView1 != null;
textureView.setSurfaceTextureListener(textureListener);
textureView1.setSurfaceTextureListener(textureListener1);
}
TextureView.SurfaceTextureListener textureListener = new TextureView.SurfaceTextureListener() {
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
//open your camera here
openCamera();
}
@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
// Transform you image captured size according to the surface width and height
}
@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
return false;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surface) {
}
};
TextureView.SurfaceTextureListener textureListener1 = new TextureView.SurfaceTextureListener() {
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
//open your camera here
openBackCamera();
}
@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
// Transform you image captured size according to the surface width and height
}
@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
return false;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surface) {
}
};
private final CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(CameraDevice camera) {
//This is called when the camera is open
Log.e(TAG, "onOpened");
cameraDevice = camera;
createCameraPreview();
}
@Override
public void onDisconnected(CameraDevice camera) {
cameraDevice.close();
}
@Override
public void onError(CameraDevice camera, int error) {
cameraDevice.close();
cameraDevice = null;
}
};
private final CameraDevice.StateCallback stateCallback1 = new CameraDevice.StateCallback() {
@Override
public void onOpened(CameraDevice camera) {
//This is called when the camera is open
Log.e(TAG, "onOpened");
cameraDevice1 = camera;
createCameraPreview1();
}
@Override
public void onDisconnected(CameraDevice camera) {
cameraDevice1.close();
}
@Override
public void onError(CameraDevice camera, int error) {
cameraDevice1.close();
cameraDevice1 = null;
}
};
protected void startBackgroundThread() {
mBackgroundThread = new HandlerThread("Camera Background");
mBackgroundThread.start();
mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}
protected void stopBackgroundThread() {
mBackgroundThread.quitSafely();
try {
mBackgroundThread.join();
mBackgroundThread = null;
mBackgroundHandler = null;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
protected void startBackgroundThread1() {
mBackgroundThread1 = new HandlerThread("Camera Background");
mBackgroundThread1.start();
mBackgroundHandler1 = new Handler(mBackgroundThread1.getLooper());
}
protected void stopBackgroundThread1() {
mBackgroundThread1.quitSafely();
try {
mBackgroundThread1.join();
mBackgroundThread1 = null;
mBackgroundHandler1 = null;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
protected void createCameraPreview() {
try {
SurfaceTexture texture = textureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(imageDimension.getWidth(), imageDimension.getHeight());
Surface surface = new Surface(texture);
captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
captureRequestBuilder.addTarget(surface);
cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback(){
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
//The camera is already closed
if (null == cameraDevice) {
return;
}
// When the session is ready, we start displaying the preview.
cameraCaptureSessions = cameraCaptureSession;
updatePreview();
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
Toast.makeText(MainActivity.this, "Configuration change", Toast.LENGTH_SHORT).show();
}
}, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
protected void createCameraPreview1() {
try {
SurfaceTexture texture1 = textureView1.getSurfaceTexture();
assert texture1 != null;
texture1.setDefaultBufferSize(imageDimension1.getWidth(), imageDimension1.getHeight());
Surface surface = new Surface(texture1);
captureRequestBuilder1 = cameraDevice1.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
captureRequestBuilder1.addTarget(surface);
cameraDevice1.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback(){
@Override
public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
//The camera is already closed
if (null == cameraDevice1) {
return;
}
// When the session is ready, we start displaying the preview.
cameraCaptureSessions1 = cameraCaptureSession;
updatePreview1();
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
Toast.makeText(MainActivity.this, "Configuration change", Toast.LENGTH_SHORT).show();
}
}, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void openCamera() {
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
Log.e(TAG, "is camera open");
try {
cameraId = manager.getCameraIdList()[0];
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
assert map != null;
imageDimension = map.getOutputSizes(SurfaceTexture.class)[0];
// Add permission for camera and let user grant the permission
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CAMERA_PERMISSION);
return;
}
manager.openCamera(cameraId, stateCallback, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
Log.e(TAG, "openCamera X");
}
private void openBackCamera() {
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
Log.e(TAG, "is camera open");
try {
cameraId1 = manager.getCameraIdList()[1];
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId1);
StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
assert map != null;
imageDimension1 = map.getOutputSizes(SurfaceTexture.class)[0];
// Add permission for camera and let user grant the permission
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CAMERA_PERMISSION);
return;
}
manager.openCamera(cameraId1, stateCallback1, null);
} catch (CameraAccessException e) {
e.printStackTrace();
}
Log.e(TAG, "openCamera X");
}
protected void updatePreview() {
if(null == cameraDevice) {
Log.e(TAG, "updatePreview error, return");
}
captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
try {
cameraCaptureSessions.setRepeatingRequest(captureRequestBuilder.build(), null, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
protected void updatePreview1() {
if(null == cameraDevice1) {
Log.e(TAG, "updatePreview error, return");
}
captureRequestBuilder1.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
try {
cameraCaptureSessions1.setRepeatingRequest(captureRequestBuilder1.build(), null, mBackgroundHandler1);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
if (requestCode == REQUEST_CAMERA_PERMISSION) {
if (grantResults[0] == PackageManager.PERMISSION_DENIED) {
// close the app
Toast.makeText(MainActivity.this, "Sorry!!!, you can't use this app without granting permission", Toast.LENGTH_LONG).show();
finish();
}
}
}
@Override
protected void onResume() {
super.onResume();
Log.e(TAG, "onResume");
startBackgroundThread();
startBackgroundThread1();
if (textureView.isAvailable()) {
openCamera();
} else {
textureView.setSurfaceTextureListener(textureListener);
}
if (textureView1.isAvailable()) {
openBackCamera();
} else {
textureView1.setSurfaceTextureListener(textureListener1);
}
}
@Override
protected void onPause() {
Log.e(TAG, "onPause");
//closeCamera();
stopBackgroundThread();
stopBackgroundThread1();
super.onPause();
}
}
布局文件代码：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<TextureView
android:id="@+id/texture"
android:layout_width="match_parent"
android:layout_height="200dp"
android:layout_marginBottom="10dp"/>
<TextureView
android:id="@+id/texture1"
android:layout_width="match_parent"
android:layout_height="200dp"
/>
</LinearLayout>
我得到的例外情况如下：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.camera2.CameraDevice.close()' on a null object reference
我在这一行上得到例外：
cameraDevice1.close();
答案 0 :(得分：1)
哪个cameraDevice1.close（）调用失败？你有没有接到过这款相机的开机电话？
不能保证给定的Android设备可以同时打开多个摄像头;要知道的唯一方法是尝试，如果无法完成，第二个摄像头将不会触发onOpened，它将触发onError，错误代码为TOO_MANY_CAMERAS_IN_USE。
所以，如果这里发生了这种情况，那么你将在没有onOpened的情况下获得onError，并且你的cameraDevice1将永远不会被设置。