Kein Zugriff auf Kamera

Ich bin nicht in der Lage, Zugriff auf meine Kamera in die Aktivität.immer Fehler in takepicture Methode, wie ich das Problem lösen.
CamTestActivity

public class CamTestActivity extends Activity {
    private static final String TAG = "CamTestActivity";
    Preview preview;
    Button buttonClick;
    Camera camera;
    Activity act;
    Context ctx;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ctx = this;
        act = this;
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

        setContentView(R.layout.main);

        preview = new Preview(this, (SurfaceView)findViewById(R.id.surfaceView));
        preview.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        ((FrameLayout) findViewById(R.id.layout)).addView(preview);
        preview.setKeepScreenOn(true);

        preview.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

                camera.takePicture(shutterCallback, rawCallback, jpegCallback);
            }
        });

        Toast.makeText(ctx, getString(R.string.take_photo_help), Toast.LENGTH_LONG).show();

        //     buttonClick = (Button) findViewById(R.id.btnCapture);
        //     
        //     buttonClick.setOnClickListener(new OnClickListener() {
        //         public void onClick(View v) {
        ////               preview.camera.takePicture(shutterCallback, rawCallback, jpegCallback);
        //             camera.takePicture(shutterCallback, rawCallback, jpegCallback);
        //         }
        //     });
        //     
        //     buttonClick.setOnLongClickListener(new OnLongClickListener(){
        //         @Override
        //         public boolean onLongClick(View arg0) {
        //             camera.autoFocus(new AutoFocusCallback(){
        //                 @Override
        //                 public void onAutoFocus(boolean arg0, Camera arg1) {
        //                     //camera.takePicture(shutterCallback, rawCallback, jpegCallback);
        //                 }
        //             });
        //             return true;
        //         }
        //     });
    }

    @Override
    protected void onResume() {
        super.onResume();
        int numCams = Camera.getNumberOfCameras();
        if(numCams > 0){
            try{
                camera = Camera.open(0);
                camera.startPreview();
                preview.setCamera(camera);
            } catch (RuntimeException ex){
                Toast.makeText(ctx, getString(R.string.camera_not_found), Toast.LENGTH_LONG).show();
            }
        }
    }

    @Override
    protected void onPause() {
        if(camera != null) {
            camera.stopPreview();
            preview.setCamera(null);
            camera.release();
            camera = null;
        }
        super.onPause();
    }

    private void resetCam() {
        camera.startPreview();
        preview.setCamera(camera);
    }

    private void refreshGallery(File file) {
        Intent mediaScanIntent = new Intent( Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        mediaScanIntent.setData(Uri.fromFile(file));
        sendBroadcast(mediaScanIntent);
    }

    ShutterCallback shutterCallback = new ShutterCallback() {
        public void onShutter() {
            //          Log.d(TAG, "onShutter'd");
        }
    };

    PictureCallback rawCallback = new PictureCallback() {
        public void onPictureTaken(byte[] data, Camera camera) {
            //          Log.d(TAG, "onPictureTaken - raw");
        }
    };

    PictureCallback jpegCallback = new PictureCallback() {
        public void onPictureTaken(byte[] data, Camera camera) {
            new SaveImageTask().execute(data);
            resetCam();
            Log.d(TAG, "onPictureTaken - jpeg");
        }
    };

    private class SaveImageTask extends AsyncTask<byte[], Void, Void> {

        @Override
        protected Void doInBackground(byte[]... data) {
            FileOutputStream outStream = null;

            //Write to SD Card
            try {
                File sdCard = Environment.getExternalStorageDirectory();
                File dir = new File (sdCard.getAbsolutePath() + "/camtest");
                dir.mkdirs();               

                String fileName = String.format("%d.jpg", System.currentTimeMillis());
                File outFile = new File(dir, fileName);

                outStream = new FileOutputStream(outFile);
                outStream.write(data[0]);
                outStream.flush();
                outStream.close();

                Log.d(TAG, "onPictureTaken - wrote bytes: " + data.length + " to " + outFile.getAbsolutePath());

                refreshGallery(outFile);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
            }
            return null;
        }

    }
}

Preview.java

class Preview extends ViewGroup implements SurfaceHolder.Callback {
    private final String TAG = "Preview";

    SurfaceView mSurfaceView;
    SurfaceHolder mHolder;
    Size mPreviewSize;
    List<Size> mSupportedPreviewSizes;
    Camera mCamera;

    Preview(Context context, SurfaceView sv) {
        super(context);

        mSurfaceView = sv;
//       addView(mSurfaceView);

        mHolder = mSurfaceView.getHolder();
        mHolder.addCallback(this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void setCamera(Camera camera) {
        mCamera = camera;
        if (mCamera != null) {
            mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
            requestLayout();

            //get Camera parameters
            Camera.Parameters params = mCamera.getParameters();

            List<String> focusModes = params.getSupportedFocusModes();
            if (focusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO)) {
                //set the focus mode
                params.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);
                //set Camera parameters
                mCamera.setParameters(params);
            }
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        //We purposely disregard child measurements because act as a
        //wrapper to a SurfaceView that centers the camera preview instead
        //of stretching it.
        final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);

        if (mSupportedPreviewSizes != null) {
            mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, width, height);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (changed && getChildCount() > 0) {
            final View child = getChildAt(0);

            final int width = r - l;
            final int height = b - t;

            int previewWidth = width;
            int previewHeight = height;
            if (mPreviewSize != null) {
                previewWidth = mPreviewSize.width;
                previewHeight = mPreviewSize.height;
            }

            //Center the child SurfaceView within the parent.
            if (width * previewHeight > height * previewWidth) {
                final int scaledChildWidth = previewWidth * height / previewHeight;
                child.layout((width - scaledChildWidth) / 2, 0,
                        (width + scaledChildWidth) / 2, height);
            } else {
                final int scaledChildHeight = previewHeight * width / previewWidth;
                child.layout(0, (height - scaledChildHeight) / 2,
                        width, (height + scaledChildHeight) / 2);
            }
        }
    }

    public void surfaceCreated(SurfaceHolder holder) {
        //The Surface has been created, acquire the camera and tell it where
        //to draw.
        try {
            if (mCamera != null) {
                mCamera.setPreviewDisplay(holder);
            }
        } catch (IOException exception) {
            Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        //Surface will be destroyed when we return, so stop the preview.
        if (mCamera != null) {
            mCamera.stopPreview();
        }
    }


    private Size getOptimalPreviewSize(List<Size> sizes, int w, int h) {
        final double ASPECT_TOLERANCE = 0.1;
        double targetRatio = (double) w / h;
        if (sizes == null) return null;

        Size optimalSize = null;
        double minDiff = Double.MAX_VALUE;

        int targetHeight = h;

        //Try to find an size match aspect ratio and size
        for (Size size : sizes) {
            double ratio = (double) size.width / size.height;
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE) continue;
            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        //Cannot find the one match the aspect ratio, ignore the requirement
        if (optimalSize == null) {
            minDiff = Double.MAX_VALUE;
            for (Size size : sizes) {
                if (Math.abs(size.height - targetHeight) < minDiff) {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }
        return optimalSize;
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        if(mCamera != null) {
            Camera.Parameters parameters = mCamera.getParameters();
            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
            requestLayout();

            mCamera.setParameters(parameters);
            mCamera.startPreview();
        }
    }

}

dies ist logcat.

12-15 15:10:10.010: E/AndroidRuntime(1857): FATAL EXCEPTION: main
12-15 15:10:10.010: E/AndroidRuntime(1857): Process: com.example.cam, PID: 1857
12-15 15:10:10.010: E/AndroidRuntime(1857): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.takePicture(android.hardware.Camera$ShutterCallback, android.hardware.Camera$PictureCallback, android.hardware.Camera$PictureCallback)' on a null object reference
12-15 15:10:10.010: E/AndroidRuntime(1857):     at com.example.cam.CamTestActivity$4.onClick(CamTestActivity.java:62)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.view.View.performClick(View.java:4756)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.view.View$PerformClick.run(View.java:19749)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.os.Handler.handleCallback(Handler.java:739)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.os.Handler.dispatchMessage(Handler.java:95)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.os.Looper.loop(Looper.java:135)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at android.app.ActivityThread.main(ActivityThread.java:5221)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at java.lang.reflect.Method.invoke(Native Method)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at java.lang.reflect.Method.invoke(Method.java:372)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
12-15 15:10:10.010: E/AndroidRuntime(1857):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)