我正在尝试制作一款可以检测脸部的应用。下面的代码没有错误，我可以看到应该工作正常。但是，当我运行它时，我得到以下内容：
致命的例外：主要 过程：org.bytefish.videofacedetection，PID：12075 java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.hardware.Camera.setFaceDetectionListener（android.hardware.Camera $ FaceDetectionListener）＆＃39; 在null对象引用上 在org.bytefish.videofacedetection。 CameraActivity.surfaceCreated（CameraActivity.java:100） 在android.view.SurfaceView.updateWindow（SurfaceView.java:582）
在android.view.SurfaceView $ 3.onPreDraw（SurfaceView.java:177）
在 android.view.ViewTreeObserver.dispatchOnPreDraw（ViewTreeObserver.java:944） 在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:2055） 在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1107）
在 android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:6013） 在 android.view.Choreographer $ CallbackRecord.run（Choreographer.java:858） 在android.view.Choreographer.doCallbacks（Choreographer.java:670）
在android.view.Choreographer.doFrame（Choreographer.java:606）
在 android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:844） 在android.os.Handler.handleCallback（Handler.java:739）
在android.os.Handler.dispatchMessage（Handler.java:95）
在android.os.Looper.loop（Looper.java:148）
在android.app.ActivityThread.main（ActivityThread.java:5417）
at java.lang.reflect.Method.invoke（Native Method）
在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616）
代码如下，全部大写评论显示第100行和错误
import android.app.Activity;
import android.content.Context;
import android.hardware.Camera;
import android.hardware.Camera.Face;
import android.hardware.Camera.FaceDetectionListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.Log;
import android.view.OrientationEventListener;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.ViewGroup.LayoutParams;
import android.widget.Toast;
import java.util.List;
public class CameraActivity extends Activity
implements SurfaceHolder.Callback {
public static final String TAG = CameraActivity.class.getSimpleName();
private Camera mCamera;
// We need the phone orientation to correctly draw the overlay:
private int mOrientation;
private int mOrientationCompensation;
private OrientationEventListener mOrientationEventListener;
// Let's keep track of the display rotation and orientation also:
private int mDisplayRotation;
private int mDisplayOrientation;
// Holds the Face Detection result:
private Camera.Face[] mFaces;
// The surface view for the camera data
private SurfaceView mView;
// Draw rectangles and other fancy stuff:
private FaceOverlayView mFaceView;
// Log all errors:
private final CameraErrorCallback mErrorCallback = new CameraErrorCallback();
/**
* Sets the faces for the overlay view, so it can be updated
* and the face overlays will be drawn again.
*/
private FaceDetectionListener faceDetectionListener = new FaceDetectionListener() {
@Override
public void onFaceDetection(Face[] faces, Camera camera) {
Log.d("onFaceDetection", "Number of Faces:" + faces.length);
// Update the view now!
mFaceView.setFaces(faces);
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mView = new SurfaceView(this);
setContentView(mView);
// Now create the OverlayView:
mFaceView = new FaceOverlayView(this);
addContentView(mFaceView, new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
// Create and Start the OrientationListener:
mOrientationEventListener = new SimpleOrientationEventListener(this);
mOrientationEventListener.enable();
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
SurfaceHolder holder = mView.getHolder();
holder.addCallback(this);
}
@Override
protected void onPause() {
mOrientationEventListener.disable();
super.onPause();
}
@Override
protected void onResume() {
mOrientationEventListener.enable();
super.onResume();
}
@Override
public void surfaceCreated(SurfaceHolder surfaceHolder) {
mCamera = Camera.open();
mCamera.setFaceDetectionListener(faceDetectionListener);
mCamera.startFaceDetection();
try {
mCamera.setPreviewDisplay(surfaceHolder);
} catch (Exception e) {
Log.e(TAG, "Could not preview the image.", e);
}
}
@Override
public void surfaceChanged(SurfaceHolder surfaceHolder, int format, int width, int height) {
// We have no surface, return immediately:
if (surfaceHolder.getSurface() == null) {
return;
}
// Try to stop the current preview:
try {
mCamera.stopPreview();
} catch (Exception e) {
// Ignore...
}
configureCamera(width, height);
setDisplayOrientation();
setErrorCallback();
// Everything is configured! Finally start the camera preview again:
mCamera.startPreview();
}
private void setErrorCallback() {
mCamera.setErrorCallback(mErrorCallback);
}
private void setDisplayOrientation() {
// Now set the display orientation:
mDisplayRotation = Util.getDisplayRotation(CameraActivity.this);
mDisplayOrientation = Util.getDisplayOrientation(mDisplayRotation, 0);
mCamera.setDisplayOrientation(mDisplayOrientation);
if (mFaceView != null) {
mFaceView.setDisplayOrientation(mDisplayOrientation);
}
}
private void configureCamera(int width, int height) {
Camera.Parameters parameters = mCamera.getParameters();
// Set the PreviewSize and AutoFocus:
setOptimalPreviewSize(parameters, width, height);
setAutoFocus(parameters);
// And set the parameters:
mCamera.setParameters(parameters);
}
private void setOptimalPreviewSize(Camera.Parameters cameraParameters, int width, int height) {
List<Camera.Size> previewSizes = cameraParameters.getSupportedPreviewSizes();
float targetRatio = (float) width / height;
Camera.Size previewSize = Util.getOptimalPreviewSize(this, previewSizes, targetRatio);
cameraParameters.setPreviewSize(previewSize.width, previewSize.height);
}
private void setAutoFocus(Camera.Parameters cameraParameters) {
cameraParameters.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);
}
@Override
public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
mCamera.setPreviewCallback(null);
mCamera.setFaceDetectionListener(null);
mCamera.setErrorCallback(null);
mCamera.release();
mCamera = null;
}
/**
* We need to react on OrientationEvents to rotate the screen and
* update the views.
*/
private class SimpleOrientationEventListener extends OrientationEventListener {
public SimpleOrientationEventListener(Context context) {
super(context, SensorManager.SENSOR_DELAY_NORMAL);
}
@Override
public void onOrientationChanged(int orientation) {
// We keep the last known orientation. So if the user first orient
// the camera then point the camera to floor or sky, we still have
// the correct orientation.
if (orientation == ORIENTATION_UNKNOWN) return;
mOrientation = Util.roundOrientation(orientation, mOrientation);
// When the screen is unlocked, display rotation may change. Always
// calculate the up-to-date orientationCompensation.
int orientationCompensation = mOrientation
+ Util.getDisplayRotation(CameraActivity.this);
if (mOrientationCompensation != orientationCompensation) {
mOrientationCompensation = orientationCompensation;
mFaceView.setOrientation(mOrientationCompensation);
}
}
}
}
当我尝试在android studio中打开它时，它打开正常，没有错误，但当我尝试运行它时死亡。
我是Android的新手，所以任何提示都会非常感激。非常感谢您的帮助和时间。
答案 0 :(得分：2)
好吧，看起来你没有正确使用相机对象
此代码将正确启动前置摄像头 的 part1的
cameraId = findFrontFacingCamera();
if (cameraId < 0) {
Toast.makeText(this, "No camera found.",
Toast.LENGTH_LONG).show();
} else {
mcamera = Camera.open(cameraId);
}
<强>第2部分
private int findFrontFacingCamera() {
int cameraId = -1;
// Search for the front facing camera
int numberOfCameras = Camera.getNumberOfCameras();
for (int i = 0; i < numberOfCameras; i++) {
CameraInfo info = new CameraInfo();
Camera.getCameraInfo(i, info);
if (info.facing == CameraInfo.CAMERA_FACING_FRONT) {
Log.d(DEBUG_TAG, "Camera found");
cameraId = i;
break;
}
}
return cameraId;
}
请尝试让我知道。