Question

I want to stream the camera preview of the android camera, onto a view. The intention is to afterwards add various things to the view, using onDraw(). I don’t need to actually capture the image at any time.
It doesn’t have to be in the highest quality or largest number of frames per second.
Does anyone have an idea how this can be done?

Answer 1

add this to your xml:

<SurfaceView
    android:id="@+id/camerapreview"  
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
/>

---

into your activity-class:

private Preview mPreview;
Camera mCamera;
int numberOfCameras;
int cameraCurrentlyLocked;
int defaultCameraId;

---

onCreate-Method:

mPreview = new Preview(this);
setContentView(mPreview);

mPreview.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        mCamera.autoFocus(null);
    }
});

---

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

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

---

and the preview-class:

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

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

    public 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);
    }

    @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) {
        // Now that the size is known, set up the camera parameters and begin
        // the preview.
        if(mCamera != null){
            Camera.Parameters parameters = mCamera.getParameters();
            parameters.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
            requestLayout();

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

}