title: Android load only visible elements of ListView
body: <p>I'm using Lazy Loading List in my application and I need to load only the visible elements of ListView.I've search over the internet,tried a lot of things but still cannot get the things to work.Can you give me a suggestion how to do it?</p>
  
  <p>Here is the ImageLoader class :</p>
  
  <pre><code>package com.stampii.stampii.tableview;
  
  import java.io.File;
  import java.io.InputStream;
  import java.util.HashMap;
  import java.util.Stack;
  import javax.crypto.Cipher;
  import javax.crypto.CipherInputStream;
  import javax.crypto.spec.IvParameterSpec;
  import javax.crypto.spec.SecretKeySpec;
  import com.stampii.stampii.R;
  import android.app.Activity;
  import android.content.Context;
  import android.content.res.AssetManager;
  import android.graphics.Bitmap;
  import android.graphics.BitmapFactory;
  import android.util.Log;
  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;
      private AssetManager mAssetManager;
  
  
      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);
          mAssetManager = context.getAssets();
  
          //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(),"Stampii");
          else
              cacheDir=context.getCacheDir();
          if(!cacheDir.exists())
              cacheDir.mkdirs();
      }
  
  
      final int stub_id=R.drawable.default_img;
      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)  //opashka
      {
          //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 src) {
          Bitmap myBitmap = null;
  
  
                  //Decryption
                  try {
                  Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
                  SecretKeySpec keySpec = new SecretKeySpec("01234567890abcde".getBytes(), "AES");
                  IvParameterSpec ivSpec = new IvParameterSpec("fedcba9876543210".getBytes());
                  cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
  
                  InputStream input = mAssetManager.open(src);
                  CipherInputStream cis = new CipherInputStream(input, cipher);
  
                  myBitmap = BitmapFactory.decodeStream(cis);
  
                  }
                  catch(Exception e){
                      e.printStackTrace();
                      Log.v("ERROR","Error : "+e);
                  }
  
  
                  return myBitmap;
  
  
          }
  
      //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);
                          Object tag=photoToLoad.imageView.getTag();
                          if(tag!=null &amp;&amp; ((String)tag).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
  
          long size=0;
              cache.clear();
  
              //clear SD cache
              File[] files=cacheDir.listFiles();
              for(File f:files){
                  size=size+f.length();
                      f.delete();
              }
      }
  
  
  
  
  }
  </code></pre>
  
  <p><strong>EDIT1:</strong></p>
  
  <p>getView method in my LazyAdapter class :</p>
  
  <pre><code>   public View getView(int position, View convertView, ViewGroup parent) {
          View vi=convertView;
          ViewHolder holder;
          if(convertView==null){
              vi = inflater.inflate(R.layout.item, null);
              holder=new ViewHolder();
              holder.name=(TextView)vi.findViewById(R.id.name);
              holder.info=(TextView)vi.findViewById(R.id.info);
              holder.image=(ImageView)vi.findViewById(R.id.image);
              vi.setTag(holder);
          }
          else
              holder=(ViewHolder)vi.getTag();
  
          holder.name.setText("MotoGP Rider");
          holder.info.setText("Category");
          holder.image.setTag(data[position]);
          imageLoader.DisplayImage(data[position], activity, holder.image);
          return vi;
      }
  </code></pre>
  
  <p>Any ideas?</p>