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POAndroid First In First Out Lazyloading
 

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  1. POAndroid First In First Out Lazyloading
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    <p>Refering to the lazyloading method at <a href="http://open-pim.com/tmp/LazyList.zip" rel="nofollow noreferrer">http://open-pim.com/tmp/LazyList.zip</a>, discussed at <a href="https://stackoverflow.com/questions/541966/android-how-do-i-do-a-lazy-load-of-images-in-listview">Lazy load of images in ListView</a> by Fedor</p> <p>I would like to know whether the following code can be changed from Last In First Out (LIFO) to First In First Out (FIFO) when displaying images downloaded from web</p> <p>public class ImageLoader {</p> <pre><code>//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){ 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(),"More"); 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 instream = null; HttpGet httpRequest = new HttpGet(new URI(url)); HttpClient httpclient = new DefaultHttpClient(); HttpResponse response = (HttpResponse) httpclient.execute(httpRequest); HttpEntity entity = response.getEntity(); BufferedHttpEntity bufHttpEntity = new BufferedHttpEntity(entity); try { instream = bufHttpEntity.getContent(); } catch (Exception e) { } finally { if (instream != null) { instream.close(); } } OutputStream os = new FileOutputStream(f); Utils.CopyStream(instream, 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*=2; } //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); 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 cache.clear(); //clear SD cache File[] files=cacheDir.listFiles(); for(File f:files) f.delete(); } </code></pre> <p>}</p>
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