Android Camera is null?

Question

I have spent some time debugging and can't figure why null is occurring. When I run the application immeditaley it crashes and it points to this line:

 mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();

and says the object reference is null. I can't figure out why mCamera is returning null.

My Manifest file has the proper permissions:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />
<uses-feature android:name="android.hardware.camera.front" android:required="false" />

Example:

import java.io.File;
        import java.io.FileNotFoundException;
        import java.io.FileOutputStream;
        import java.io.IOException;
        import java.text.SimpleDateFormat;
        import java.util.Date;

        import android.app.Activity;
        import android.content.Context;
        import android.content.pm.PackageManager;
        import android.hardware.Camera;
        import android.hardware.Camera.CameraInfo;
        import android.hardware.Camera.PictureCallback;
        import android.os.Bundle;
        import android.view.View;
        import android.view.View.OnClickListener;
        import android.view.WindowManager;
        import android.widget.Button;
        import android.widget.LinearLayout;
        import android.widget.Toast;

public class AndroidCameraExample extends Activity {
    private Camera mCamera;
    private CameraPreview mPreview;
    private PictureCallback mPicture;
    private Button capture, switchCamera;
    private Context myContext;
    private LinearLayout cameraPreview;
    private boolean cameraFront = false;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        myContext = this;
        initialize();
    }

    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) {
                cameraId = i;
                cameraFront = true;
                break;
            }
        }
        return cameraId;
    }

    private int findBackFacingCamera() {
        int cameraId = -1;
        //Search for the back facing camera
        //get the number of cameras
        int numberOfCameras = Camera.getNumberOfCameras();
        //for every camera check
        for (int i = 0; i < numberOfCameras; i++) {
            CameraInfo info = new CameraInfo();
            Camera.getCameraInfo(i, info);
            if (info.facing == CameraInfo.CAMERA_FACING_BACK) {
                cameraId = i;
                cameraFront = false;
                break;
            }
        }
        return cameraId;
    }

    public void onResume() {
        super.onResume();
        if (!hasCamera(myContext)) {
            Toast toast = Toast.makeText(myContext, "Sorry, your phone does not have a camera!", Toast.LENGTH_LONG);
            toast.show();
            finish();
        }
        if (mCamera == null) {
            //if the front facing camera does not exist
            if (findFrontFacingCamera() < 0) {
                Toast.makeText(this, "No front facing camera found.", Toast.LENGTH_LONG).show();
                switchCamera.setVisibility(View.GONE);
            }
            mCamera = Camera.open(findBackFacingCamera());
            mPicture = getPictureCallback();
            mPreview.refreshCamera(mCamera);
        }
    }

    public void initialize() {
        cameraPreview = (LinearLayout) findViewById(R.id.camera_preview);
        mPreview = new CameraPreview(myContext, mCamera);
        cameraPreview.addView(mPreview);

        capture = (Button) findViewById(R.id.button_capture);
        capture.setOnClickListener(captrureListener);

        switchCamera = (Button) findViewById(R.id.button_ChangeCamera);
        switchCamera.setOnClickListener(switchCameraListener);
    }

    OnClickListener switchCameraListener = new OnClickListener() {
        @Override
        public void onClick(View v) {
            //get the number of cameras
            int camerasNumber = Camera.getNumberOfCameras();
            if (camerasNumber > 1) {
                //release the old camera instance
                //switch camera, from the front and the back and vice versa

                releaseCamera();
                chooseCamera();
            } else {
                Toast toast = Toast.makeText(myContext, "Sorry, your phone has only one camera!", Toast.LENGTH_LONG);
                toast.show();
            }
        }
    };

    public void chooseCamera() {
        //if the camera preview is the front
        if (cameraFront) {
            int cameraId = findBackFacingCamera();
            if (cameraId >= 0) {
                //open the backFacingCamera
                //set a picture callback
                //refresh the preview

                mCamera = Camera.open(cameraId);
                mPicture = getPictureCallback();
                mPreview.refreshCamera(mCamera);
            }
        } else {
            int cameraId = findFrontFacingCamera();
            if (cameraId >= 0) {
                //open the backFacingCamera
                //set a picture callback
                //refresh the preview

                mCamera = Camera.open(cameraId);
                mPicture = getPictureCallback();
                mPreview.refreshCamera(mCamera);
            }
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        //when on Pause, release camera in order to be used from other applications
        releaseCamera();
    }

    private boolean hasCamera(Context context) {
        //check if the device has camera
        if (context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
            return true;
        } else {
            return false;
        }
    }

    private PictureCallback getPictureCallback() {
        PictureCallback picture = new PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {
                //make a new picture file
                File pictureFile = getOutputMediaFile();

                if (pictureFile == null) {
                    return;
                }
                try {
                    //write the file
                    FileOutputStream fos = new FileOutputStream(pictureFile);
                    fos.write(data);
                    fos.close();
                    Toast toast = Toast.makeText(myContext, "Picture saved: " + pictureFile.getName(), Toast.LENGTH_LONG);
                    toast.show();

                } catch (FileNotFoundException e) {
                } catch (IOException e) {
                }

                //refresh camera to continue preview
                mPreview.refreshCamera(mCamera);
            }
        };
        return picture;
    }

    OnClickListener captrureListener = new OnClickListener() {
        @Override
        public void onClick(View v) {
            mCamera.takePicture(null, null, mPicture);
        }
    };

    //make picture and save to a folder
    private static File getOutputMediaFile() {
        //make a new file directory inside the "sdcard" folder
        File mediaStorageDir = new File("/sdcard/", "JCG Camera");

        //if this "JCGCamera folder does not exist
        if (!mediaStorageDir.exists()) {
            //if you cannot make this folder return
            if (!mediaStorageDir.mkdirs()) {
                return null;
            }
        }

        //take the current timeStamp
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        File mediaFile;
        //and make a media file:
        mediaFile = new File(mediaStorageDir.getPath() + File.separator + "IMG_" + timeStamp + ".jpg");

        return mediaFile;
    }

    private void releaseCamera() {
        // stop and release camera
        if (mCamera != null) {
            mCamera.release();
            mCamera = null;
        }
    }
}

CameraPreview:

import java.io.IOException;
import java.util.List;

import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {

    private static final String TAG = "CameraPreview";

    private Context mContext;
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private List<Camera.Size> mSupportedPreviewSizes;
    private Camera.Size mPreviewSize;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mContext = context;
        mCamera = camera;


            // supported preview sizes
            mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();
            for (Camera.Size str : mSupportedPreviewSizes)
                Log.e(TAG, str.width + "/" + str.height);

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = getHolder();
        mHolder.addCallback(this);
        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // empty. surfaceChanged will take care of stuff
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        Log.e(TAG, "surfaceChanged => w=" + w + ", h=" + h);
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.
        if (mHolder.getSurface() == null){
            // preview surface does not exist
            return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
            // ignore: tried to stop a non-existent preview
        }

        // set preview size and make any resize, rotate or reformatting changes here
        // start preview with new settings
        try {
            Camera.Parameters parameters = mCamera.getParameters();
            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
            mCamera.setParameters(parameters);
            mCamera.setDisplayOrientation(90);
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();

        } catch (Exception e){
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);

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

        float ratio;
        if(mPreviewSize.height >= mPreviewSize.width)
            ratio = (float) mPreviewSize.height / (float) mPreviewSize.width;
        else
            ratio = (float) mPreviewSize.width / (float) mPreviewSize.height;

        // One of these methods should be used, second method squishes preview slightly
        setMeasuredDimension(width, (int) (width * ratio));
//        setMeasuredDimension((int) (width * ratio), height);
    }

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

        if (sizes == null)
            return null;

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

        int targetHeight = h;

        for (Camera.Size size : sizes) {
            double ratio = (double) size.height / size.width;
            if (Math.abs(ratio - targetRatio) > ASPECT_TOLERANCE)
                continue;

            if (Math.abs(size.height - targetHeight) < minDiff) {
                optimalSize = size;
                minDiff = Math.abs(size.height - targetHeight);
            }
        }

        if (optimalSize == null) {
            minDiff = Double.MAX_VALUE;
            for (Camera.Size size : sizes) {
                if (Math.abs(size.height - targetHeight) < minDiff) {
                    optimalSize = size;
                    minDiff = Math.abs(size.height - targetHeight);
                }
            }
        }

        return optimalSize;
    }

    public void refreshCamera(Camera camera) {
        if (mHolder.getSurface() == null) {
            // preview surface does not exist
            return;
        }
        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e) {
            // ignore: tried to stop a non-existent preview
        }
        // set preview size and make any resize, rotate or
        // reformatting changes here
        // start preview with new settings
        setCamera(camera);
        try {
            Camera.Parameters parameters = mCamera.getParameters();
            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
            mCamera.setParameters(parameters);
            mCamera.setDisplayOrientation(90);
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();
        } catch (Exception e) {
            Log.d(VIEW_LOG_TAG, "Error starting camera preview: " + e.getMessage());
        }
    }

    public void setCamera(Camera camera) {
        //method to set a camera instance
        mCamera = camera;
    }
}

As I am using a tutorial, if I use this CameraPreview.java instead (keeping the same Example class) it works, but I needed to make some modifications to the tutorial for the aspect ratio reasons:

import java.io.IOException;

import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;
        mHolder = getHolder();
        mHolder.addCallback(this);
        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void surfaceCreated(SurfaceHolder holder) {
        try {
            // create the surface and start camera preview
            if (mCamera == null) {
                mCamera.setPreviewDisplay(holder);
                mCamera.startPreview();
            }
        } catch (IOException e) {
            Log.d(VIEW_LOG_TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    public void refreshCamera(Camera camera) {
        if (mHolder.getSurface() == null) {
            // preview surface does not exist
            return;
        }
        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e) {
            // ignore: tried to stop a non-existent preview
        }
        // set preview size and make any resize, rotate or
        // reformatting changes here
        // start preview with new settings
        setCamera(camera);
        try {
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();
        } catch (Exception e) {
            Log.d(VIEW_LOG_TAG, "Error starting camera preview: " + e.getMessage());
        }
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.
        refreshCamera(mCamera);
    }

    public void setCamera(Camera camera) {
        //method to set a camera instance
        mCamera = camera;
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        // TODO Auto-generated method stub
        // mCamera.release();

    }
}

UPDATE: Additionally I tried to put chooseCamera(); right before the mPreview = new CameraPreview(myContext, mCamera); but it did not work.

Answer 1

I have a guess, as I haven't tested this code, but from looking at it as is, I think that you are calling initialize() before you are instantiating your actually Camera object. Observe this picture of the Android life cycle:

diagram source

You will notice that onResume() is called AFTER onCreate(). In your code you are creating the CameraPreview class with your null mCamera reference in the by calling the initialize() method in onCreate(). Therefore, the line in CameraPreview:

 mSupportedPreviewSizes = mCamera.getParameters().getSupportedPreviewSizes();

is calling a null object reference, mCamera. Instead, move

mCamera = Camera.open(findBackFacingCamera());

to onCreate() (before the call to initialize CameraPreview of course!), keeping the same call in onResume(). Keep the check for a null Camera in onResume() in case the user leaves the activity and Camera is closed for some reason.