Waiting for camera to save photo, what is better than thread.sleep? - camera

Question

I have a custom OpenCV camera activity that takes a photo when the screen is tapped. The activity is started with a startActivityForResult intent, and the filepath of the photo is handed back to the MainActivity after the activity is finished. However, the camera saves the photo asynchronously and therefore the filepath shouldn't be checked until the photo is taken. I am using the filepath to set an imageView, and calling it immediately gives an empty image. I have managed to make it work by using Thread.sleep(3000); but this is a horrible option as it just stalls the UI which, as I've read countless times, is a big no no! Is there a way I can wait until the photo is saved before calling the return to MainActivity intent? I understand there is a callback from the camera but I don't understand how it works or how to use it, perhaps that is the best way to go?
Here's some code anyway.
in MainActivity extends FragmentActivity:
rootView.findViewById(R.id.button_start_camera).setOnClickListener(new View.OnClickListener() {
// Listen for Take Photo button Click, start app's openCV camera
#Override
public void onClick(View view) {
// Start Camera app
Intent intentCamera = new Intent(getActivity(), CameraActivity.class);
startActivityForResult(intentCamera, 2);
}
});
In CameraActivity extends Activity implements CvCameraViewListener2, OnTouchListener:
#Override
public boolean onTouch(View v, MotionEvent event) {
Log.i(TAG,"onTouch event");
if (takePicture) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd-HHmmss");
String currentDateandTime = sdf.format(new Date());
fileName = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getPath() +
"/MatCom_" + currentDateandTime + ".jpg";
mOpenCvCameraView.takePicture(fileName);
Toast.makeText(this, fileName + " saved", Toast.LENGTH_SHORT).show();
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
Intent returnIntent = new Intent();
returnIntent.putExtra("result", fileName);
setResult(RESULT_OK, returnIntent);
finish();
}
return false;
}
And then back to MainActivity:
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent)
{
super.onActivityResult(requestCode, resultCode, intent);
Log.i(TAG, "onActivityResult. resultCode = " + requestCode);
if (requestCode == 1) {//My other startActivityForResult...}
if (requestCode == 131074 && resultCode == RESULT_OK){
Bundle bundle = intent.getExtras();
filepath = bundle.getString("result");
Log.i(TAG, filepath);
imageView = (ImageView) findViewById(R.id.imageView);
bmp = BitmapFactory.decodeFile(filepath);
imageView.setBackgroundResource(0);
imageView.setImageBitmap(bmp);
}
}
NOTICE: As an aside, for some reason my requestCode comes back as 131074 every time despite setting it at 2 for the startActivityForResult - let me know if you know why that is.
Finally, in case it's necessary to see, here's the takePicture method from the CameraView class:
public void takePicture(final String fileName) {
Log.i(TAG, "Taking picture");
PictureCallback callback = new PictureCallback() {
private String mPictureFileName = fileName;
#Override
public void onPictureTaken(byte[] data, Camera camera) {
Log.i(TAG, "Saving a bitmap to file");
Bitmap picture = BitmapFactory.decodeByteArray(data, 0, data.length);
try {
FileOutputStream out = new FileOutputStream(mPictureFileName);
picture.compress(Bitmap.CompressFormat.JPEG, 90, out);
picture.recycle();
// Open the image for analysis
// Read in the image from the file
Mat mOriginalImage = Highgui.imread(fileName);
// Only process the image if it actually exists!
if (mOriginalImage != null) {
// Find the size of the image
org.opencv.core.Size mSizeReadImage = mOriginalImage.size();
// From the number of rows and columns get the coordinates of the largest possible centralised square
double height = mSizeReadImage.height;
double width = mSizeReadImage.width;
double minDim = Math.min(height, width);
double top = height/2.0 - 2.0*minDim/5.0;
double left = width/2.0 - 2.0*minDim/5.0;
// Create a submat of the image based on the centralised square
Mat mOriginalImageSubmat = mOriginalImage.submat((int)Math.round(top), (int)Math.round(top + 4.0*minDim/5.0), (int)Math.round(left), (int)Math.round(left + 4.0*minDim/5.0));
// Create another Mat the required size but same type as mOriginalImageSubmat and resize mOriginalImageSubmat to fit into it
Mat mDrawableSubmat = new Mat(new Size(480.0, 480.0), mOriginalImageSubmat.type());
Imgproc.resize(mOriginalImageSubmat, mDrawableSubmat, mDrawableSubmat.size());
Mat mColourSourceSubmat = mDrawableSubmat.clone();
Mat mCannyOutput = mDrawableSubmat.clone();
double minLineLength = 300.0;
ColourMatrix matrix = new ColourMatrix();
matrix.setColourMatch(colourMatch);
matrix.setColourOrder(colourOrder);
matrix.setComparison(comparison);
matrix.setDisplayHotspots(displayHotspots);
matrix.setDisplayOutline(displayOutline);
matrix.setIntensity(intensity);
matrix.setMatrixType(matrixType);
String output = matrix.decode(mColourSourceSubmat, mCannyOutput, mDrawableSubmat, minLineLength);
Log.i(TAG, "DJH - decoded: " + output);
}
mCamera.startPreview();
} catch (Exception e) {
e.printStackTrace();
}
}
};
mCamera.takePicture(null, null, callback);
}

Answer 1

Thread.sleep isn't bad per se. You can use a loop to 30 with thread.sleep(100). Then you'll only be pausing .1 second at a time, and the CPU still won't spike.