Implementing Asynchronous Image Loading In Listview

If you are new learning in Android development then I would suggest you to refer the previous tutorials Creating ListView and custom listview. And you must have read my previous post: Android – Image Loading and Caching from Web, where I have talked about loading single images from web and caching the same into SDCard.

Today, I will talk about loading images in listview. Just think what if we dont implement asynchronous loading of images? It will suck and user will go away from your application, so do you want the same? If no then I would suggest you to implement Lazy Loading (Load images asynchronously).

In this example we just has to implement ListView and create adapter to load images and data. remaing part will be same as my previous post Image Loading and Chaching from Web

Below are the steps to implement Asynchronous image loading in Android:

Step 1: Write following into activity_main.xml to create XML layout for ListView:

 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:cacheColorHint="@android:color/transparent"
android:divider="@android:color/transparent"
android:dividerHeight="10dp"
android:fadingEdge="none"
android:listSelector="@android:color/transparent"
android:padding="10dp" >
</ListView>

</LinearLayout>

 

 

Step 2: Create and write following into row_listview_item.xml to create ListView items:

 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@drawable/btn_white_matte" >

<ImageView
android:id="@+id/image"
android:layout_width="50dip"
android:layout_height="50dip"
android:scaleType="centerCrop"
android:src="@drawable/ic_launcher" />

<TextView
android:id="@+id/text"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="left|center_vertical"
android:layout_marginLeft="10dip"
android:layout_weight="1"
android:textSize="20dip" />

</LinearLayout>

 

Step 3: Create adapter for ListView LazyAdapter.java and write following code:

 

package com.example.loadwebimage;

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

import com.example.loadwebimage.imageutils.ImageLoader;

public class LazyAdapter extends BaseAdapter {

private Activity activity;
private String[] data;
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;

public LazyAdapter(Activity a, String[] d) {
activity = a;
data=d;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(activity.getApplicationContext());
}

public int getCount() {
return data.length;
}

public Object getItem(int position) {
return position;
}

public long getItemId(int position) {
return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.row_listview_item, null);

TextView text=(TextView)vi.findViewById(R.id.text);;
ImageView image=(ImageView)vi.findViewById(R.id.image);
text.setText("item "+position);
imageLoader.DisplayImage(data[position], image);
return vi;
}
}

 

Step 4: Write following into MainActivity.java file

 

package com.example.loadwebimage;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ListView;

public class MainActivity extends Activity {

ListView list;
LazyAdapter adapter;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

list=(ListView)findViewById(R.id.listView1);
adapter=new LazyAdapter(this, imageUrls);
list.setAdapter(adapter);
}

@Override
public void onDestroy()
{
list.setAdapter(null);
super.onDestroy();
}

private String imageUrls[] = {
"https://si0.twimg.com/profile_images/2053165008/ac-new_bigger.jpg",
"https://si0.twimg.com/profile_images/1751120073/green-android-rotate-02__1__copy_9_bigger.jpeg",
"https://si0.twimg.com/profile_images/2508170683/m8jf0po4imu8t5eemjdd_bigger.png",
"https://si0.twimg.com/profile_images/1517737798/aam-twitter-right-final_bigger.png",
"https://si0.twimg.com/profile_images/1265264136/twitter_bg3_bigger.png",
"https://si0.twimg.com/profile_images/64827025/android-wallpaper6_2560x160_bigger.png",
"https://si0.twimg.com/profile_images/839219643/gals_twitter_bigger.png",
"https://si0.twimg.com/profile_images/2244328948/ADC4_Twitter_128_bigger.jpg",
"https://si0.twimg.com/profile_images/956404323/androinica-avatar_bigger.png",
"https://si0.twimg.com/profile_images/1417650153/android-hug_bigger.png",
"https://si0.twimg.com/profile_images/1084169260/twitter_logo3_bigger.png",
"https://si0.twimg.com/profile_images/895713856/android_large_bigger.png",
"https://si0.twimg.com/profile_images/328066023/droid_con150_bigger.jpg",
"https://si0.twimg.com/profile_images/909231146/Android_Biz_Man_bigger.png",
"https://si0.twimg.com/profile_images/77641093/AndroidPlanet_bigger.png",
"https://si0.twimg.com/profile_images/60788468/androffice_bigger.png",
"https://si0.twimg.com/profile_images/262620111/logodroid_bigger.png",
"https://si0.twimg.com/profile_images/1024243227/Android-Apps_bigger.jpg",
"https://si0.twimg.com/profile_images/2172264088/logo-testa-quad_bigger.png",
"https://si0.twimg.com/profile_images/1186449790/mestre-android-twitter_bigger.jpg",
"https://si0.twimg.com/profile_images/1785885571/androidvenezuela_bigger.png"
};
}

 

 

Step 5: These are the required classes for loading image asynchronously and caching into the local memory storage.

ImageLoader.java

 

package com.eaxmple.loadwebimage.imageutils;

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.HttpURLConnection;
import java.net.URL;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;

import com.example.loadwebimage.R;

public class ImageLoader {

MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;

public ImageLoader(Context context){
fileCache=new FileCache(context);
executorService=Executors.newFixedThreadPool(5);
}

final int stub_id=R.drawable.ic_launcher;
public void DisplayImage(String url, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null)
imageView.setImageBitmap(bitmap);
else
{
queuePhoto(url, imageView);
imageView.setImageResource(stub_id);
}
}

private void queuePhoto(String url, ImageView imageView)
{
PhotoToLoad p=new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}

private Bitmap getBitmap(String url)
{
File f=fileCache.getFile(url);

//from SD cache
Bitmap b = decodeFile(f);
if(b!=null)
return b;

//from web
try {
Bitmap bitmap=null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);
conn.setInstanceFollowRedirects(true);
InputStream is=conn.getInputStream();
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
bitmap = decodeFile(f);
return bitmap;
} catch (Throwable ex){
ex.printStackTrace();
if(ex instanceof OutOfMemoryError)
memoryCache.clear();
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 PhotoToLoad(String u, ImageView i){
url=u;
imageView=i;
}
}

class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad){
this.photoToLoad=photoToLoad;
}

@Override
public void run() {
if(imageViewReused(photoToLoad))
return;
Bitmap bmp=getBitmap(photoToLoad.url);
memoryCache.put(photoToLoad.url, bmp);
if(imageViewReused(photoToLoad))
return;
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
Activity a=(Activity)photoToLoad.imageView.getContext();
a.runOnUiThread(bd);
}
}

boolean imageViewReused(PhotoToLoad photoToLoad){
String tag=imageViews.get(photoToLoad.imageView);
if(tag==null || !tag.equals(photoToLoad.url))
return true;
return false;
}

//Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable
{
Bitmap bitmap;
PhotoToLoad photoToLoad;
public BitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}
public void run()
{
if(imageViewReused(photoToLoad))
return;
if(bitmap!=null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}

public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
}

 

 

MemoryCache.java

 

package com.example.loadwebimage.imageutils;

import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import android.graphics.Bitmap;
import android.util.Log;

public class MemoryCache {

private static final String TAG = "MemoryCache";
private Map<String, Bitmap> cache=Collections.synchronizedMap(
new LinkedHashMap<String, Bitmap>(10,1.5f,true));//Last argument true for LRU ordering
private long size=0;//current allocated size
private long limit=1000000;//max memory in bytes

public MemoryCache(){
//use 25% of available heap size
setLimit(Runtime.getRuntime().maxMemory()/4);
}

public void setLimit(long new_limit){
limit=new_limit;
Log.i(TAG, "MemoryCache will use up to "+limit/1024./1024.+"MB");
}

public Bitmap get(String id){
try{
if(!cache.containsKey(id))
return null;
//NullPointerException sometimes happen here http://code.google.com/p/osmdroid/issues/detail?id=78
return cache.get(id);
}catch(NullPointerException ex){
ex.printStackTrace();
return null;
}
}

public void put(String id, Bitmap bitmap){
try{
if(cache.containsKey(id))
size-=getSizeInBytes(cache.get(id));
cache.put(id, bitmap);
size+=getSizeInBytes(bitmap);
checkSize();
}catch(Throwable th){
th.printStackTrace();
}
}

private void checkSize() {
Log.i(TAG, "cache size="+size+" length="+cache.size());
if(size>limit){
Iterator<Entry<String, Bitmap>> iter=cache.entrySet().iterator();//least recently accessed item will be the first one iterated
while(iter.hasNext()){
Entry<String, Bitmap> entry=iter.next();
size-=getSizeInBytes(entry.getValue());
iter.remove();
if(size<=limit)
break;
}
Log.i(TAG, "Clean cache. New size "+cache.size());
}
}

public void clear() {
try{
//NullPointerException sometimes happen here http://code.google.com/p/osmdroid/issues/detail?id=78
cache.clear();
size=0;
}catch(NullPointerException ex){
ex.printStackTrace();
}
}

long getSizeInBytes(Bitmap bitmap) {
if(bitmap==null)
return 0;
return bitmap.getRowBytes() * bitmap.getHeight();
}
}

 

 

FileCache.java

 

package com.example.loadwebimage.imageutils;

import java.io.File;
import android.content.Context;

public class FileCache {

private File cacheDir;

public FileCache(Context context){
//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(),"TTImages_cache");
else
cacheDir=context.getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();
}

public File getFile(String url){
//I identify images by hashcode. Not a perfect solution, good for the demo.
String filename=String.valueOf(url.hashCode());
//Another possible solution (thanks to grantland)
//String filename = URLEncoder.encode(url);
File f = new File(cacheDir, filename);
return f;

}

public void clear(){
File[] files=cacheDir.listFiles();
if(files==null)
return;
for(File f:files)
f.delete();
}
}

 

 

Utils.java

 

package com.example.loadwebimage.imageutils;

import java.io.InputStream;
import java.io.OutputStream;

public class Utils {
public static void CopyStream(InputStream is, OutputStream os)
{
final int buffer_size=1024;
try
{
byte[] bytes=new byte[buffer_size];
for(;;)
{
int count=is.read(bytes, 0, buffer_size);
if(count==-1)
break;
os.write(bytes, 0, count);
}
}
catch(Exception ex){}
}
}

 

 

Include INTERNET and WRITE_EXTERNAL_STORAGE permission in AndroidManifest.xml

 

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

 

 

Output:

async1

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