Question

I am using imageLoader class to load image in background, after that i am setting image in emulator its working. In device its not showing lazy downloaded image.

private void queuePhoto(String url, Activity activity, ImageView imageView) 
{
    photosQueue.Clean(imageView);
    PhotoToLoad p=new PhotoToLoad(url, imageView);
    synchronized(photosQueue.photosToLoad)
    {
        photosQueue.photosToLoad.push(p);
        photosQueue.photosToLoad.notifyAll();
    }
    (photoLoaderThread.getState()==Thread.State.NEW)
    photoLoaderThread.start();
}

Answer 1

Here’s my version of ImageLoader I accompany every ImageView with progressbar. Animations then applied for transitions. I also removed the SD card caching option. You should see most remnant of my modifications.

/*
 * Copyright (c)2012 Poohdish Rattanavijai
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.robgthai.lib.util;

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.util.Log;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.ImageView;
import android.widget.ProgressBar;

import com.robgthai.lib.R;

/**
 * This class help handling the Lazyload of the image from given URL
 * @author Poohdish Rattanavijai
 *
 */
public class ImageLoader {
    private static final String TAG = ImageLoader.class.getSimpleName();
    private static final int LOG_LEVEL = (HelperUtil.FORCE_EVERY_LOG? Log.DEBUG: Log.INFO);
    //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;
    private Context context;

    final int stub_id=R.drawable.ic_refresh; // Default icon to display before the image finish loaded

    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);
        this.context = context;
        cacheDir=new File(context.getCacheDir(),"LazyList");

        //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();
    }

    /**
     * Method for lazy-loading images
     * @param url URL of the image
     * @param activity Activity context, currently unused
     * @param imageView ImageView to display the image
     * @param progressBar ProgressBar for displaying while the image is being load
     */
    public void DisplayImage(String url, Activity activity, ImageView imageView, ProgressBar progressBar)
    {
        if(cache.containsKey(url)) //If image is already in the cache
            imageView.setImageBitmap(cache.get(url));
        else
        {
            queuePhoto(url, activity, imageView, progressBar);
            imageView.setImageResource(stub_id);
        }    
    }

    /**
     * Method for lazy-loading images with the image sliding in from the left replacing the progress bar
     * @param url URL of the image
     * @param context Activity context, currently unused
     * @param imageView ImageView to display the image
     * @param progressBar ProgressBar for displaying while the image is being load
     */
    public void DisplayImage(String url, Context context, ImageView imageView, ProgressBar progressBar)
    {
        if(cache.containsKey(url)){
            if(LOG_LEVEL <= Log.DEBUG)Log.d(TAG, "Found in cache: " + url + "[" + cache.get(url) + "]");
            imageView.setImageBitmap(cache.get(url));

            Animation exitAnim = AnimationUtils.loadAnimation(ImageLoader.this.context, R.anim.list_image_slide_left_exit);
            exitAnim.setFillAfter(true);
            exitAnim.setFillEnabled(true);

            Animation enterAnim = AnimationUtils.loadAnimation(ImageLoader.this.context, R.anim.list_image_slide_left_enter);
            enterAnim.setFillAfter(true);
            enterAnim.setFillEnabled(true);
            progressBar.setVisibility(View.GONE);
            imageView.setVisibility(View.VISIBLE);

            progressBar.startAnimation(exitAnim);
            imageView.startAnimation(enterAnim);
//            if(bitmap!=null){
//                imageView.setImageBitmap(bitmap);
//                if(null != progress){
//                  progress.startAnimation(exitAnim);
//                  progress.setVisibility(View.GONE);
//                }
//                imageView.startAnimation(enterAnim);
////                imageView.setVisibility(View.VISIBLE);
//            }else{
//                if(null != progress){
//                  progress.startAnimation(enterAnim);
////                    progress.setVisibility(View.VISIBLE);
//                    imageView.setVisibility(View.GONE);
//                }else{
//                    imageView.setImageResource(stub_id);
//                    imageView.startAnimation(enterAnim);
////                    imageView.setVisibility(View.VISIBLE);
//                }
//            }
        }else
        {
            queuePhoto(url, context, imageView, progressBar);
            imageView.setImageResource(stub_id);
        }    
    }

    /**
     * Queue the image to download
     * @param url
     * @param context
     * @param imageView
     * @param progressBar
     */
    private void queuePhoto(String url, Context context, ImageView imageView, ProgressBar progressBar)
    {
        //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= null;
        if(null != progressBar){
            p = new PhotoToLoad(url, imageView, progressBar);
        }else{
            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();
    }

    /**
     * Queue the image to download
     * @param url
     * @param context
     * @param imageView
     * @param progressBar
     */    
    private void queuePhoto(String url, Activity activity, ImageView imageView, ProgressBar progressBar)
    {
        //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= null;
        if(null != progressBar){
            p = new PhotoToLoad(url, imageView, progressBar);
        }else{
            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();
    }

    /**
     * Load image into the view preferably from Cache, otherwise url.
     * @param url
     * @return
     */
    private Bitmap getBitmap(String url) 
    {
        //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 cache
        Bitmap b = decodeFile(f);
        if(LOG_LEVEL <= Log.DEBUG)Log.d(TAG, "Looking for Image in cache");
        if(b!=null){
            if(LOG_LEVEL <= Log.DEBUG)Log.d(TAG, "Image found");
            return b;
        }

        //from web
        try {
            if(LOG_LEVEL <= Log.DEBUG)Log.d(TAG, "Image not found, download from: " + url);
            Bitmap bitmap=null;
            InputStream is=new URL(url).openStream();
            OutputStream os = new FileOutputStream(f);
            HelperUtil.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*=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 ProgressBar progress;
        public PhotoToLoad(String u, ImageView i, ProgressBar p){
            url=u; 
            imageView=i;
            progress = p;
        }
        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;
            }
        }
    }

    /**
     * Controller of the image loader 
     * @author poohdishr
     *
     */
    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 && ((String)tag).equals(photoToLoad.url)){
                            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView, photoToLoad.progress);
                            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;
        ProgressBar progress;
        public BitmapDisplayer(Bitmap b, ImageView i, ProgressBar p){bitmap=b;imageView=i;progress=p;}
        public void run()
        {
            Animation exitAnim = AnimationUtils.loadAnimation(ImageLoader.this.context, R.anim.list_image_slide_left_exit);
            exitAnim.setFillAfter(true);
            exitAnim.setFillEnabled(true);

            Animation enterAnim = AnimationUtils.loadAnimation(ImageLoader.this.context, R.anim.list_image_slide_left_enter);
            enterAnim.setFillAfter(true);
            enterAnim.setFillEnabled(true);
            if(bitmap!=null){
                imageView.setImageBitmap(bitmap);
                if(null != progress){
                    progress.startAnimation(exitAnim);
                    progress.setVisibility(View.GONE);
                }
                imageView.startAnimation(enterAnim);
                imageView.setVisibility(View.VISIBLE);
            }else{
                if(null != progress){
                    progress.startAnimation(enterAnim);
//                  progress.setVisibility(View.VISIBLE);
                    imageView.setVisibility(View.GONE);
                }else{
                    imageView.setImageResource(stub_id);
                    imageView.startAnimation(enterAnim);
//                    imageView.setVisibility(View.VISIBLE);
                }
            }
        }
    }

    public void clearCache() {
        //clear memory cache
        cache.clear();

        //clear SD cache
        File[] files=cacheDir.listFiles();
        for(File f:files)
            f.delete();
    }

}