How can I set the camera preview size to fullscreen with Android API?

Question

I am very new to Android development, and I am trying to get a simple camera application setup. So far I have a working camera application that has "switch camera" and "take picture" buttons inside the menu which are working fine.

The only problem I am having, is I am trying to figure out how to get the display to be fullscreen. Right now, the camera is only showing up in the very middle of the screen, and is only taking up about 1/4 of the screen.

MainActivity Code

package assist.core;

import android.app.Activity;
import android.app.AlertDialog;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.hardware.Camera.ShutterCallback;
import android.hardware.Camera.CameraInfo;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.util.Log;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class MainActivity extends Activity {

    private final String TAG = "MainActivity";
    private Preview mPreview;
    Camera mCamera;
    int numberOfCameras;
    int cameraCurrentlyLocked;

    //The first rear facing camera
    int defaultCameraId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //Hide the window title.
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

        //Create a RelativeLayout container that will hold a SurfaceView,
        //and set it as the content of our activity.
        mPreview = new Preview(this);
        setContentView(mPreview);

        //Find the total number of cameras available
        numberOfCameras = Camera.getNumberOfCameras();

        //Find the ID of the default camera
        CameraInfo cameraInfo = new CameraInfo();
        for (int i = 0; i < numberOfCameras; i++) {
            Camera.getCameraInfo(i, cameraInfo);
            if(cameraInfo.facing == CameraInfo.CAMERA_FACING_BACK) {
                defaultCameraId = i;
            }
        }
    }

    @Override
    protected void onResume() {
        super.onResume();

        //Open the default i.e. the first rear facing camera.
        mCamera = Camera.open();
        cameraCurrentlyLocked = defaultCameraId;
        mPreview.setCamera(mCamera);
    }

    @Override
    protected void onPause() {
        super.onPause();

        //Because the Camera object is a shared resource, it's very
        //Important to release it when the activity is paused.
        if (mCamera != null) {
            mPreview.setCamera(null);
            mCamera.release();
            mCamera = null;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        //Inflate our menu which can gather user input for switching camera
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.camera_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        //Handle item selection
        switch (item.getItemId()) {
            case R.id.switchCam:
                //Check for availability of multiple cameras
                if (numberOfCameras == 1) {
                    AlertDialog.Builder builder = new AlertDialog.Builder(this);
                    builder.setMessage(this.getString(R.string.camera_alert)).setNeutralButton("Close", null);
                    AlertDialog alert = builder.create();
                    alert.show();
                    return true;
                }

                //OK, we have multiple cameras.
                //Release this camera -> cameraCurrentlyLocked
                if (mCamera != null) {
                    mCamera.stopPreview();
                    mPreview.setCamera(null);
                    mCamera.release();
                    mCamera = null;
                }

                //Acquire the next camera and request Preview to reconfigure parameters.
                mCamera = Camera.open((cameraCurrentlyLocked + 1) % numberOfCameras);
                cameraCurrentlyLocked = (cameraCurrentlyLocked + 1) % numberOfCameras;
                mPreview.switchCamera(mCamera);

                //Start the preview
                mCamera.startPreview();
                return true;

            case R.id.takePicture:
                mCamera.takePicture(shutterCallback, rawCallback, jpegCallback);
                return true;

            default:
                return super.onOptionsItemSelected(item);
        }
    }

    /**
     * Called when shutter is opened
     */
    ShutterCallback shutterCallback = new ShutterCallback() { 
        public void onShutter() {
        }
    };

    /**
     * Handles data for raw picture when the picture is taken
     */
    PictureCallback rawCallback = new PictureCallback() { 
        public void onPictureTaken(byte[] data, Camera camera) {
        }
    };

    /**
     * Handles data for jpeg picture when the picture is taken
     */
    PictureCallback jpegCallback = new PictureCallback() { 
        public void onPictureTaken(byte[] data, Camera camera) {
            FileOutputStream outStream = null;
            try {
                // Write to SD Card
                outStream = new FileOutputStream(String.format("/sdcard/%d.jpg",
                System.currentTimeMillis()));
                outStream.write(data);
                outStream.close();
            } 
            catch (FileNotFoundException e) { 
                Log.e(TAG, "IOException caused by PictureCallback()", e);
            } 
            catch (IOException e) {
                Log.e(TAG, "IOException caused by PictureCallback()", e);
            } 
        }
    };
}

Preview Class Code

package assist.core;

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

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

/**
 *
 * @author cmetrolis
 */
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) {
        super(context);

        mSurfaceView = new SurfaceView(context);
        addView(mSurfaceView);

        //Install a SurfaceHolder.Callback so we get notified when the
        //underlying surface is created and destroyed.
        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();
        }
    }

    public void switchCamera(Camera camera) {
       setCamera(camera);
       try {
           camera.setPreviewDisplay(mHolder);
       } 
       catch (IOException exception) {
           Log.e(TAG, "IOException caused by setPreviewDisplay()", exception);
       }
       Camera.Parameters parameters = camera.getParameters();
       parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
       requestLayout();

       camera.setParameters(parameters);
    }

    /**
     * Called to determine the size requirements for this view and all of its children.
     * @param widthMeasureSpec
     * @param heightMeasureSpec 
     */
    @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);
        }
    }

    /**
     * Called when this view should assign a size and position to all of its children.
     * @param changed
     * @param l
     * @param t
     * @param r
     * @param b 
     */
    @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);
            }
        }
    } 

    /**
     * This is called immediately after the surface is first created
     * @param holder 
     */
    public void surfaceCreated(SurfaceHolder holder) { 
        try {
            if(mCamera != null) {
                mCamera.setPreviewDisplay(holder); 
            }
        } 
        catch (IOException e) {
            Log.e(TAG, "IOException caused by setPreviewDisplay()", e);
        }
    }

    /**
     * This is called immediately before a surface is being destroyed
     * @param holder 
     */
    public void surfaceDestroyed(SurfaceHolder holder) {
        //Surface will be destroyed when we return, so stop the preview.
        if(mCamera != null) {
            mCamera.stopPreview();
            mCamera.release();
        }
    }

    /**
     * This is called immediately after any structural changes (format or size) have been made to the surface
     * @param holder
     * @param format
     * @param w
     * @param h 
     */
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { 
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
        mCamera.setDisplayOrientation(90);
        requestLayout();

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

    /**
     * Returns the best preview size
     * @param sizes
     * @param w
     * @param h
     * @return Size
     */
    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;
    }
}

camer_menu.xml code

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <item android:id="@+id/switchCam"
          android:title="@string/switch_cam" />

    <item android:id="@+id/takePicture"
          android:title="@string/take_picture" 
          android:onClick="snapPicture" 
          android:layout_gravity="center" />
</menu>

UPDATE

I tried changing the code in the Preview constructor to the following.

ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
this.setLayoutParams(lp);

mSurfaceView = new SurfaceView(context);
mSurfaceView.setLayoutParams(lp);
addView(mSurfaceView);

This did not crash, but it also did not make the camera fullscreen.

Answer 1

I fixed it by removing the following code from the Preview class,

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

Answer 2

Since you're using setContentView with your custom Preview class that derives from ViewGroup, just pass a ViewGroup.LayoutParams telling it to fill it's parent.

Something like this:

ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
Preview.setLayoutParams(lp);