title: Android Lazy Loading
body: <p>I have implemented concept of lazy loading in my project, and I'm showing an image through URL in List view through lazy loading. All are working absolutely fine.</p>
  
  <p>But now problem is I want to pass the image from one screen to another which is downloaded from URL.</p>
  
  <p>I'm not able to do that. For your reference, I'm pasting the code:</p>
  
  <pre><code>package com.android.istock;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.net.URL;
  import java.util.HashMap;
  import java.util.Stack;
  import android.app.Activity;
  import android.content.Context;
  import android.graphics.Bitmap;
  import android.graphics.BitmapFactory;
  import android.widget.ImageView;
  
  public class ImageLoader {
  
      //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
      private HashMap&lt;String, Bitmap&gt; cache=new HashMap&lt;String, Bitmap&gt;();
  
      private File cacheDir;
  
      public ImageLoader(Context context){
          //Make the background thead low priority. This way it will not affect the UI performance
          photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);
  
          //Find the dir to save cached images
          if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
              cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
          else
              cacheDir=context.getCacheDir();
          if(!cacheDir.exists())
              cacheDir.mkdirs();
      }
  
      final int stub_id=R.drawable.stub;
      public void DisplayImage(String url, Activity activity, ImageView imageView)
      {
          if(cache.containsKey(url))
              imageView.setImageBitmap(cache.get(url));
          else
          {
              queuePhoto(url, activity, imageView);
              imageView.setImageResource(stub_id);
          }    
      }
  
      private void queuePhoto(String url, Activity activity, ImageView imageView)
      {
          //This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them. 
          photosQueue.Clean(imageView);
          PhotoToLoad p=new PhotoToLoad(url, imageView);
          synchronized(photosQueue.photosToLoad){
              photosQueue.photosToLoad.push(p);
              photosQueue.photosToLoad.notifyAll();
          }
  
          //start thread if it's not started yet
          if(photoLoaderThread.getState()==Thread.State.NEW)
              photoLoaderThread.start();
      }
  
      private Bitmap getBitmap(String url) 
      {
          //I identify images by hashcode. Not a perfect solution, good for the demo.
          String filename=String.valueOf(url.hashCode());
          File f=new File(cacheDir, filename);
  
          //from SD cache
          Bitmap b = decodeFile(f);
          if(b!=null)
              return b;
  
          //from web
          try {
              Bitmap bitmap=null;
              InputStream is=new URL(url).openStream();
              OutputStream os = new FileOutputStream(f);
              Utils.CopyStream(is, os);
              os.close();
              bitmap = decodeFile(f);
              return bitmap;
          } catch (Exception ex){
             ex.printStackTrace();
             return null;
          }
      }
  
      //decodes image and scales it to reduce memory consumption
      private Bitmap decodeFile(File f){
          try {
              //decode image size
              BitmapFactory.Options o = new BitmapFactory.Options();
              o.inJustDecodeBounds = true;
              BitmapFactory.decodeStream(new FileInputStream(f),null,o);
  
              //Find the correct scale value. It should be the power of 2.
              final int REQUIRED_SIZE=70;
              int width_tmp=o.outWidth, height_tmp=o.outHeight;
              int scale=1;
              while(true){
                  if(width_tmp/2&lt;REQUIRED_SIZE || height_tmp/2&lt;REQUIRED_SIZE)
                      break;
                  width_tmp/=2;
                  height_tmp/=2;
                  scale++;
              }
  
              //decode with inSampleSize
              BitmapFactory.Options o2 = new BitmapFactory.Options();
              o2.inSampleSize=scale;
              return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
          } catch (FileNotFoundException e) {}
          return null;
      }
  
      //Task for the queue
      private class PhotoToLoad
      {
          public String url;
          public ImageView imageView;
          public PhotoToLoad(String u, ImageView i){
              url=u; 
              imageView=i;
          }
      }
  
      PhotosQueue photosQueue=new PhotosQueue();
  
      public void stopThread()
      {
          photoLoaderThread.interrupt();
      }
  
      //stores list of photos to download
      class PhotosQueue
      {
          private Stack&lt;PhotoToLoad&gt; photosToLoad=new Stack&lt;PhotoToLoad&gt;();
  
          //removes all instances of this ImageView
          public void Clean(ImageView image)
          {
              for(int j=0 ;j&lt;photosToLoad.size();){
                  if(photosToLoad.get(j).imageView==image)
                      photosToLoad.remove(j);
                  else
                      ++j;
              }
          }
      }
  
      class PhotosLoader extends Thread {
          public void run() {
              try {
                  while(true)
                  {
                      //thread waits until there are any images to load in the queue
                      if(photosQueue.photosToLoad.size()==0)
                          synchronized(photosQueue.photosToLoad){
                              photosQueue.photosToLoad.wait();
                          }
                      if(photosQueue.photosToLoad.size()!=0)
                      {
                          PhotoToLoad photoToLoad;
                          synchronized(photosQueue.photosToLoad){
                              photoToLoad=photosQueue.photosToLoad.pop();
                          }
                          Bitmap bmp=getBitmap(photoToLoad.url);
                          cache.put(photoToLoad.url, bmp);
                          if(((String)photoToLoad.imageView.getTag()).equals(photoToLoad.url)){
                              BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
                              Activity a=(Activity)photoToLoad.imageView.getContext();
                              a.runOnUiThread(bd);
                          }
                      }
                      if(Thread.interrupted())
                          break;
                  }
              } catch (InterruptedException e) {
                  //allow thread to exit
              }
          }
      }
  
      PhotosLoader photoLoaderThread=new PhotosLoader();
  
      //Used to display bitmap in the UI thread
      class BitmapDisplayer implements Runnable
      {
          Bitmap bitmap;
          ImageView imageView;
          public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
          public void run()
          {
              if(bitmap!=null)
                  imageView.setImageBitmap(bitmap);
              else
                  imageView.setImageResource(stub_id);
          }
      }
  
      public void clearCache() {
          //clear memory cache
          cache.clear();
  
          //clear SD cache
          File[] files=cacheDir.listFiles();
          for(File f:files)
              f.delete();
      }
  
  }
  </code></pre>
  
  <p>Now I want to use the image in next screen. How can I do that?</p>