Preview.java

package jjil.android;

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

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

/**
 * A simple wrapper around a Camera and a SurfaceView that renders a centered preview of the Camera
 * to the surface. We need to center the SurfaceView because not all devices have cameras that
 * support preview sizes at the same aspect ratio as the device's display.
 */
public class Preview extends ViewGroup implements SurfaceHolder.Callback {
    private final String TAG = "Preview";

    public interface PreviewSizeChangedCallback {
        void previewSizeChanged();
    }
    
    private Camera mCamera;
    private SurfaceHolder mHolder;
    private Size mPreviewSize;
    private PreviewSizeChangedCallback mPreviewSizeChangedCallback = null;
    private List<Size> mSupportedPreviewSizes;
    private SurfaceView mSurfaceView;
    
    public Preview(Context context, AttributeSet attributeSet) {
        super(context, attributeSet);
        mSurfaceView = new SurfaceView(context, attributeSet);
        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);
       }
       if (mSupportedPreviewSizes != null) {
           mPreviewSize = getOptimalPreviewSize(mSupportedPreviewSizes, 
                   getMeasuredWidth(), getMeasuredHeight());
       }
       Camera.Parameters parameters = camera.getParameters();
       parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
       requestLayout();

       try
       {
           camera.setParameters(parameters);
       }
       catch (RuntimeException e)
       {
           Log.e(TAG, "error setting parameters", e);
       }
    }

    @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 setPreviewSizeChangedCallback(PreviewSizeChangedCallback callback) {
        mPreviewSizeChangedCallback = callback;
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        if (mCamera != null) {
            // Now that the size is known, set up the camera parameters and
            // begin
            // the preview.
            Camera.Parameters parameters = mCamera.getParameters();
            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
            requestLayout();

            try
            {
                mCamera.setParameters(parameters);
            }
            catch (RuntimeException e)
            {
                Log.e(TAG, "error setting parameters", e);
            }

            mCamera.startPreview();
            if (mPreviewSizeChangedCallback != null) {
                mPreviewSizeChangedCallback.previewSizeChanged();
            }
        }
    }

}