code: /*
   *
   *     Copyright (C) 2015 Ingo Fuchs
   *     This program is free software; you can redistribute it and/or modify
   *     it under the terms of the GNU General Public License as published by
   *     the Free Software Foundation; either version 2 of the License, or
   *     (at your option) any later version.
   *
   *     This program is distributed in the hope that it will be useful,
   *     but WITHOUT ANY WARRANTY; without even the implied warranty of
   *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *     GNU General Public License for more details.
   *
   *     You should have received a copy of the GNU General Public License along
   *     with this program; if not, write to the Free Software Foundation, Inc.,
   *     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
   * /
   */
  
  package freed.cam.ui.guide;
  
  import android.content.res.Resources;
  import android.graphics.Bitmap;
  import android.graphics.BitmapFactory;
  import android.os.AsyncTask;
  import android.widget.ImageView;
  
  import java.lang.ref.WeakReference;
  
  /**
   * Created by troop on 01.09.2016.
   */
  public class BitmapRessourceWorkerTask extends AsyncTask<Integer, Void, Bitmap> {
      private final WeakReference<ImageView> imageViewReference;
      private final int w;
      private final int h;
      private final Resources resources;
  
      public BitmapRessourceWorkerTask(ImageView imageView, Resources resources) {
          // Use a WeakReference to ensure the ImageView can be garbage collected
          imageViewReference = new WeakReference<>(imageView);
          w = imageView.getWidth();
          h = imageView.getHeight();
          this.resources = resources;
      }
  
      // Decode image in background.
      @Override
      protected Bitmap doInBackground(Integer... params) {
          int data = params[0];
          if (w == 0 || h == 0)
              return null;
          return decodeSampledBitmapFromResource(resources, data, w, h);
      }
  
      // Once complete, see if ImageView is still around and set bitmap.
      @Override
      protected void onPostExecute(Bitmap bitmap) {
          if (imageViewReference != null && bitmap != null) {
              final ImageView imageView = imageViewReference.get();
              if (imageView != null) {
                  imageView.setImageBitmap(bitmap);
              }
          }
      }
  
      private Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
                                                           int reqWidth, int reqHeight) {
  
          // First decode with inJustDecodeBounds=true to check dimensions
          final BitmapFactory.Options options = new BitmapFactory.Options();
          options.inJustDecodeBounds = true;
          BitmapFactory.decodeResource(res, resId, options);
  
          // Calculate inSampleSize
          options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
  
          // Decode bitmap with inSampleSize set
          options.inJustDecodeBounds = false;
          return BitmapFactory.decodeResource(res, resId, options);
      }
  
      private int calculateInSampleSize(
              BitmapFactory.Options options, int reqWidth, int reqHeight) {
          // Raw height and width of image
          final int height = options.outHeight;
          final int width = options.outWidth;
          int inSampleSize = 1;
  
          if (height > reqHeight || width > reqWidth) {
  
              final int halfHeight = height / 2;
              final int halfWidth = width / 2;
  
              // Calculate the largest inSampleSize value that is a power of 2 and keeps both
              // height and width larger than the requested height and width.
              while ((halfHeight / inSampleSize) >= reqHeight
                      && (halfWidth / inSampleSize) >= reqWidth) {
                  inSampleSize *= 2;
              }
          }
  
          return inSampleSize;
      }
  }
  