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POImageview gets set multiple time using AsyncTask in Android
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copied!<p>I followed the procedure <a href="http://android-developers.blogspot.in/2010/07/multithreading-for-performance.html" rel="nofollow">here</a> and set up an easy AsyncTask Image downloader/loader for me. I call the download function from inside my GetView of the Adapter. Thus, everytime I scroll up or down, once the view goes out of screen, the images vanish only to be set again when I scroll back to that item. How do I stop this and, once I've all the images downloaded/cached, to set it. I don't want my ImageViews to be reset every single time. </p> <p>This is the ImageManager:</p> <pre><code>import java.io.File; import java.io.FileOutputStream; import java.net.URL; import java.util.HashMap; import java.util.Stack; import android.R; import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.widget.ImageView; public class ImageManager { private HashMap<String, Bitmap> imageMap = new HashMap<String, Bitmap>(); private File cacheDir; public Thread imageLoaderThread = new Thread() ; public ImageQueue imageQueue = new ImageQueue(); public ImageManager(Context context) { // Make background thread low priority, to avoid affecting UI performance imageLoaderThread.setPriority(Thread.NORM_PRIORITY-1); // Find the dir to save cached images String sdState = android.os.Environment.getExternalStorageState(); if (sdState.equals(android.os.Environment.MEDIA_MOUNTED)) { File sdDir = android.os.Environment.getExternalStorageDirectory(); cacheDir = new File(sdDir,"data/codehenge"); } else cacheDir = context.getCacheDir(); if(!cacheDir.exists()) cacheDir.mkdirs(); } private void queueImage(String url, ImageView imageView) { // This ImageView might have been used for other images, so we clear // the queue of old tasks before starting. imageQueue.Clean(imageView); ImageRef p=new ImageRef(url, imageView); synchronized(imageQueue.imageRefs) { imageQueue.imageRefs.push(p); imageQueue.imageRefs.notifyAll(); } // Start thread if it's not started yet if(imageLoaderThread.getState() == Thread.State.NEW) imageLoaderThread.start(); } private class ImageRef { public String url; public ImageView imageView; public ImageRef(String u, ImageView i) { url=u; imageView=i; } } private class ImageQueue { private Stack<ImageRef> imageRefs = new Stack<ImageRef>(); //removes all instances of this ImageView public void Clean(ImageView view) { for(int i = 0 ;i < imageRefs.size();) { if(imageRefs.get(i).imageView == view) imageRefs.remove(i); else ++i; } } } private class ImageQueueManager implements Runnable { @Override public void run() { try { while(true) { // Thread waits until there are images in the // queue to be retrieved if(imageQueue.imageRefs.size() == 0) { synchronized(imageQueue.imageRefs) { imageQueue.imageRefs.wait(); } } // When we have images to be loaded if(imageQueue.imageRefs.size() != 0) { ImageRef imageToLoad; synchronized(imageQueue.imageRefs) { imageToLoad = imageQueue.imageRefs.pop(); } Bitmap bmp = getBitmap(imageToLoad.url); imageMap.put(imageToLoad.url, bmp); Object tag = imageToLoad.imageView.getTag(); // Make sure we have the right view - thread safety defender if(tag != null && ((String)tag).equals(imageToLoad.url)) { BitmapDisplayer bmpDisplayer = new BitmapDisplayer(bmp, imageToLoad.imageView); Activity a = (Activity)imageToLoad.imageView.getContext(); a.runOnUiThread(bmpDisplayer); } } if(Thread.interrupted()) break; } } catch (InterruptedException e) {} } private Bitmap getBitmap(String url) { String filename = String.valueOf(url.hashCode()); File f = new File(cacheDir, filename); // Is the bitmap in our cache? Bitmap bitmap = BitmapFactory.decodeFile(f.getPath()); if(bitmap != null) return bitmap; // Nope, have to download it try { bitmap = BitmapFactory.decodeStream(new URL(url).openConnection().getInputStream()); // save bitmap to cache for later writeFile(bitmap, f); return bitmap; } catch (Exception ex) { ex.printStackTrace(); return null; } } private void writeFile(Bitmap bmp, File f) { FileOutputStream out = null; try { out = new FileOutputStream(f); bmp.compress(Bitmap.CompressFormat.PNG, 80, out); } catch (Exception e) { e.printStackTrace(); } finally { try { if (out != null ) out.close(); } catch(Exception ex) {} } } } public void displayImage(String url, Activity activity, ImageView imageView) { if(imageMap.containsKey(url)) { Bitmap bitmapToShow = imageMap.get(url); if(bitmapToShow != null) { //> Image was cached well imageView.setImageBitmap(bitmapToShow); return; } } //> Image was cached failed else { imageView.setImageResource(R.drawable.btn_radio); queueImage(url,imageView); return; } } private 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(R.drawable.spinner_background); } } } </code></pre> <p>My View:</p> <pre><code>if( v == null){ LayoutInflater li = (LayoutInflater)c.getSystemService(Context.LAYOUT_INFLATER_SERVICE); v = li.inflate(R.layout.list_item,null); holder = new ViewHolder(); holder.name = (TextView)v.findViewById(R.id.name); holder.text = (TextView)v.findViewById(R.id.text); holder.displayPic = (ImageView)v.findViewById(R.id.DisplayPicture); v.setTag(holder); } else { holder = (ViewHolder)v.getTag(); obj = objs.get(position); if (obj != null) { holder.name.setText(obj.Name); holder.text.setText(""+obj.snippet); holder.displayPic.setTag(obj.ImageUrl); imageManager.displayImage(obj.ImageUrl, activity, holder.displayPic); } } </code></pre>

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