for (int i = 0; i < gridView.getChildCount(); i++) {
   View child = gridView.getChildAt(i);
   CheckBox checkBox = (CheckBox) child.findViewById(R.id.checkBox);

   if(checkBox.isChecked())
       // do something
}

    void imageProcessing()
    {
        // Creation of a "bitmap" object containing the pixels from "image.png"

        BitmapFactory bf = new BitmapFactory();
        BitmapFactory.Options bfo = new BitmapFactory.Options();

        bfo.inMutable = true;
        bfo.inPreferredConfig = ARGB_8888;

        Bitmap bm = bf.decodeFile("/storage/emulated/0/DCIM/image.png", bfo);

        // The 32 bits int which will contain values of red, green, blue, alpha
        int pixel_color;

        // The alpha, red, green, blue values
        int alpha, red, green, blue;

        // Color selected : full blue, with an alpha of 127 (the pixel will be half-transparent)
        red = 0; green = 0; blue = 255; alpha = 127;

        // Putting the A, R, G, B values into the int variable "pixel_color"
        pixel_color = (alpha<<24) | (red<<16) | (green<<8) | blue;

        // Modifying the (x=3,y=0) pixel with this color
        bm.setPixel(3, 0, pixel_color);

        // Recording the modified image as "new_image.png"

        ByteArrayOutputStream outStream = new ByteArrayOutputStream();

        bm.compress(Bitmap.CompressFormat.PNG, 100, outStream);

        File f = new File("/storage/emulated/0/DCIM/new_image.png");

        try {
            f.createNewFile();
            FileOutputStream fo = new FileOutputStream(f);
            fo.write(outStream.toByteArray());
            fo.flush();
            fo.close();
        } catch (FileNotFoundException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        } catch (IOException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        }
    }

    void imageProcessing()
    {
        // Creation of a "bitmap" object containing the pixels from "parrot.jpeg"

        BitmapFactory bf1 = new BitmapFactory();
        BitmapFactory.Options bfo1 = new BitmapFactory.Options();

        bfo1.inMutable = true;
        bfo1.inPreferredConfig = ARGB_8888;
        bfo1.outConfig = ARGB_8888;

        Bitmap bm1 = bf1.decodeFile("/storage/emulated/0/DCIM/parrot.jpeg", bfo1);

        // Recording the image with the png format, as "parrot.png"

        ByteArrayOutputStream outStream = new ByteArrayOutputStream();

        bm1.compress(Bitmap.CompressFormat.PNG, 100, outStream);

        File f = new File("/storage/emulated/0/DCIM/parrot.png");

        try {
            f.createNewFile();
            FileOutputStream fo = new FileOutputStream(f);
            fo.write(outStream.toByteArray());
            fo.flush();
            fo.close();
        } catch (FileNotFoundException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        } catch (IOException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        }

        // Creation of a "bitmap" object containing the pixels from "parrot.png"

        BitmapFactory bf2 = new BitmapFactory();
        BitmapFactory.Options bfo2 = new BitmapFactory.Options();

        bfo2.inMutable = true;
        bfo2.inPreferredConfig = ARGB_8888;
        bfo2.outConfig = ARGB_8888;

        Bitmap bm2 = bf2.decodeFile("/storage/emulated/0/DCIM/parrot.png", bfo2);

        // The 32 bits int which will contain values of red, green, blue, alpha
        int pixel_color;

        // The alpha, red, green, blue values
        int alpha, red, green, blue;

        // Color selected : full blue, with an alpha of 127 (the pixel will be half-transparent)
        red = 0; green = 0; blue = 255; alpha = 127;

        // Putting the A, R, G, B values into the int variable "pixel_color"
        pixel_color = (alpha<<24) | (red<<16) | (green<<8) | blue;

        // Modifying the (x=3,y=0) pixel with this color
        bm2.setPixel(3, 0, pixel_color);

        // Recording the modified image as "new_parrot.png"

        ByteArrayOutputStream outStream2 = new ByteArrayOutputStream();

        bm2.compress(Bitmap.CompressFormat.PNG, 100, outStream2);

        File f2 = new File("/storage/emulated/0/DCIM/new_parrot.png");

        try {
            f2.createNewFile();
            FileOutputStream fo = new FileOutputStream(f2);
            fo.write(outStream2.toByteArray());
            fo.flush();
            fo.close();
        } catch (FileNotFoundException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        } catch (IOException e) {
            Log.w("TAG", "Error saving image file: " + e.getMessage());
        }
    }

 @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        if(isVisibleToUser){
            getFragmentManager().beginTransaction().detach(this).attach(this).commit();
        }
    }