Android: Help in adapting ListView adapter with an ImageLoader Class (LazyList)

Question

I have a custom ListView adapter which implements an ImageThreadLoader class. Unfortunately the class doesn\'t enable a cache option-download the images from the web and sav

Answer 1

Seems that you did not use any view holder in your adapter

I have made changes in your classes.Hope it will works for you with out any difficulties

The ImageThreadLoader class

 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 ImageThreadLoader {

    //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
    /** The cache. */
    private HashMap cache=new HashMap();

    /** The cache dir. */
    private File cacheDir;

    /**
     * Instantiates a new image loader.
     *
     * @param context the context
     */
    public ImageThreadLoader(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(),"cache_dir_img");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }
    //This is used for a stub when the user can not see the actual image..
    //this images will be seen
    final int stub_id =R.drawable.sample_image;


    /**
     * Display image.
     *
     * @param url the url
     * @param activity the activity
     * @param imageView the image view
     */
    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);
        }    
    }

    /**
     * Queue photo.
     *
     * @param url the url
     * @param activity the activity
     * @param imageView the image view
     */
    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();
    }

    /**
     * Gets the bitmap.
     *
     * @param url the url
     * @return the bitmap
     */
    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);
            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
    /**
     * Decode file.
     *
     * @param f the f
     * @return the bitmap
     */
    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 photosToLoad=new Stack();

        //removes all instances of this ImageView
        /**
         * Clean.
         *
         * @param image the image
         */
        public void Clean(ImageView image)
        {
            for(int j=0 ;j

Now your ProjectAdapter class

import java.util.List;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class ProjectAdapter extends ArrayAdapter {

    int resource;
    String response;
    Context context;
    List items;
    private ImageThreadLoader imageLoader;
    LayoutInflater mInflater;
    Activity activity;

    // Initialize adapter
    public ProjectAdapter(Context context, int resource, List items,
            Activity activity) {
        super(context, resource, items);
        this.resource = resource;
        imageLoader = new ImageThreadLoader(context);
        this.items = items;
        mInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        this.activity = activity;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder holder = null;

        // Inflate the view
        if (convertView == null) {

            convertView = mInflater.inflate(resource, null);
            holder = new ViewHolder();
            holder.image = (ImageView) convertView.findViewById(R.id.image);
            holder.textTitle = (TextView) convertView
                    .findViewById(R.id.txt_title);
            convertView.setTag(holder);

        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        Project project = items.get(position);

        holder.textTitle.setText(project.project_title);

        String imageurl = project.smallImageUrl;
        holder.image.setTag(imageurl);
        imageLoader.displayImage(imageurl, activity, holder.image);
        return convertView;

    }

    static class ViewHolder {

        TextView textTitle;

        ImageView image;
    }

And at last when you set the adapter in your ListView after getting the web data, use this

your_listview.setAdapter(your_ProjectAdapter_instance );
your_ProjectAdapter_instance .notifyDataSetChanged();