Hi, I'm using lazy-loading for images in a listview. The weird thing is, the first row and the last row visible on the screen seem to have the same image(of the last row on the screen). I'm using following class for image loading:
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<String, Bitmap> cache=new HashMap<String, Bitmap>();
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.default_user_pic;
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);
HeaderController.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<REQUIRED_SIZE || height_tmp/2<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<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();
//removes all instances of this ImageView
public void Clean(ImageView image)
{
for(int j=0 ;j<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();
}
}
Here is the my Expandable listview adapter code:
import java.util.List;
import java.util.Map;
import android.app.Activity;
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.SimpleExpandableListAdapter;
import android.widget.TextView;
public class NearbyAdapter extends SimpleExpandableListAdapter {
private List<? extends List<? extends Map<String, ?>>> mChildData;
private String[] mChildFrom;
private int[] mChildTo;
NearbyActivity currentActivity;
public ImageLoader imageLoader;
public NearbyAdapter(Activity activity,Context context,
List<? extends Map<String, ?>> groupData, int groupLayout,
String[] groupFrom, int[] groupTo,
List<? extends List<? extends Map<String, ?>>> childData,
int childLayout, String[] childFrom, int[] childTo) {
super(context, groupData, groupLayout, groupFrom, groupTo,
childData, childLayout, childFrom, childTo);
mChildData = childData;
mChildFrom = childFrom;
mChildTo = childTo;
currentActivity = (NearbyActivity)activity;
imageLoader=new ImageLoader(activity.getApplicationContext());
}
public View getChildView(int groupPosition, int childPosition,
boolean isLastChild, View convertView, ViewGroup parent) {
View v;
if (convertView == null) {
v = newChildView(isLastChild, parent);
} else {
v = convertView;
}
bindView(v, mChildData.get(groupPosition).get(childPosition),mChildFrom,
mChildTo, groupPosition, childPosition);
return v;
}
private void bindView(View view, Map<String, ?> data,
String[] from, int[] to, int groupPosition, int childPosition) {
if(from[3] != null)
view.setTag(data.get(from[4]));
ImageView imageView = (ImageView) view.findViewById(to[3]);
if (imageView != null) {
imageView.setTag((String) data.get(from[3]));
imageLoader.DisplayImage((String) data.get(from[3]), currentActivity, imageView);
}
}
public boolean isChildSelectable(int groupPosition, int childPosition) {
return true;
}
public boolean isGroupSelectable(int groupPosition) {
return true;
}
public boolean hasStableIds() {
return true;
}
}