技术概述:
1.使用了线程池来管理下载任务
2.使用LruCache来缓存图片
3.使用手机来缓存图片
4.GridView滑动的时候取消下载任务，静止的时候进行下载，GridView滑动更加的流畅
5.降低了代码的耦合性，结构更加的清晰，便于以后重用
接下来我们先来看看项目的结构:
FileUtils 文件操作的工具类，提供保存图片，获取图片，判断图片是否存在，删除图片的一些方法，这个类比较简单
package com.example.asyncimageloader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.Environment;
public class FileUtils {
/**
* sd卡的根目录
*/
private static String mSdRootPath = Environment.getExternalStorageDirectory().getPath();
/**
* 手机的缓存根目录
*/
private static String mDataRootPath = null;
/**
* 保存Image的目录名
*/
private final static String FOLDER_NAME = "/AndroidImage";
public FileUtils(Context context){
mDataRootPath = context.getCacheDir().getPath();
}
/**
* 获取储存Image的目录
* @return
*/
private String getStorageDirectory(){
return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) ?
mSdRootPath + FOLDER_NAME : mDataRootPath + FOLDER_NAME;
}
/**
* 保存Image的方法，有sd卡存储到sd卡，没有就存储到手机目录
* @param fileName
* @param bitmap
* @throws IOException
*/
public void savaBitmap(String fileName,Bitmap bitmap) throws IOException{
if(bitmap == null){
return;
}
String path = getStorageDirectory();
File folderFile = new File(path);
if(!folderFile.exists()){
folderFile.mkdir();
}
File file = new File(path + File.separator + fileName);
file.createNewFile();
FileOutputStream fos = new FileOutputStream(file);
bitmap.compress(CompressFormat.JPEG,100,fos);
fos.flush();
fos.close();
}
/**
* 从手机或者sd卡获取Bitmap
* @param fileName
* @return
*/
public Bitmap getBitmap(String fileName){
return BitmapFactory.decodeFile(getStorageDirectory() + File.separator + fileName);
}
/**
* 判断文件是否存在
* @param fileName
* @return
*/
public boolean isFileExists(String fileName){
return new File(getStorageDirectory() + File.separator + fileName).exists();
}
/**
* 获取文件的大小
* @param fileName
* @return
*/
public long getFileSize(String fileName) {
return new File(getStorageDirectory() + File.separator + fileName).length();
}
/**
* 删除SD卡或者手机的缓存图片和目录
*/
public void deleteFile() {
File dirFile = new File(getStorageDirectory());
if(! dirFile.exists()){
return;
}
if (dirFile.isDirectory()) {
String[] children = dirFile.list();
for (int i = 0; i < children.length; i++) {
new File(dirFile,children[i]).delete();
}
}
dirFile.delete();
}
}Images类，提供图片资源的类，来自Android文档中BitmapFun中http://developer.android.com/training/displaying-bitmaps/index.html，里面一个静态的图片Url数组，这里面比较坑爹，因为是图片是google官网提供的，有时候会下载超时
package com.example.asyncimageloader;
public class Images {
public final static String[] imageThumbUrls = new String[] {
"https://lh6.googleusercontent.com/-55osAWw3x0Q/URquUtcFr5I/AAAAAAAAAbs/rWlj1RUKrYI/s160-c/A%252520Photographer.jpg","https://lh4.googleusercontent.com/--dq8niRp7W4/URquVgmXvgI/AAAAAAAAAbs/-gnuLQfNnBA/s160-c/A%252520Song%252520of%252520Ice%252520and%252520Fire.jpg","https://lh5.googleusercontent.com/-7qZeDtRKFKc/URquWZT1gOI/AAAAAAAAAbs/hqWgteyNXsg/s160-c/Another%252520Rockaway%252520Sunset.jpg","https://lh3.googleusercontent.com/--L0Km39l5J8/URquXHGcdNI/AAAAAAAAAbs/3ZrSJNrSomQ/s160-c/Antelope%252520Butte.jpg","https://lh6.googleusercontent.com/-8HO-4vIFnlw/URquZnsFgtI/AAAAAAAAAbs/WT8jViTF7vw/s160-c/Antelope%252520Hallway.jpg","https://lh4.googleusercontent.com/-WIuWgVcU3Qw/URqubRVcj4I/AAAAAAAAAbs/YvbwgGjwdIQ/s160-c/Antelope%252520Walls.jpg","https://lh6.googleusercontent.com/-UBmLbPELvoQ/URqucCdv0kI/AAAAAAAAAbs/IdNhr2VQoQs/s160-c/Apre%2525CC%252580s%252520la%252520Pluie.jpg","https://lh3.googleusercontent.com/-s-AFpvgSeew/URquc6dF-JI/AAAAAAAAAbs/Mt3xNGRUd68/s160-c/Backlit%252520Cloud.jpg","https://lh5.googleusercontent.com/-bvmif9a9YOQ/URquea3heHI/AAAAAAAAAbs/rcr6wyeQtAo/s160-c/Bee%252520and%252520Flower.jpg","https://lh5.googleusercontent.com/-n7mdm7I7FGs/URqueT_BT-I/AAAAAAAAAbs/9MYmXlmpSAo/s160-c/Bonzai%252520Rock%252520Sunset.jpg","https://lh6.googleusercontent.com/-4CN4X4t0M1k/URqufPozWzI/AAAAAAAAAbs/8wK41lg1KPs/s160-c/Caterpillar.jpg","https://lh3.googleusercontent.com/-rrFnVC8xQEg/URqufdrLBaI/AAAAAAAAAbs/s69WYy_fl1E/s160-c/Chess.jpg","https://lh5.googleusercontent.com/-WVpRptWH8Yw/URqugh-QmDI/AAAAAAAAAbs/E-MgBgtlUWU/s160-c/Chihuly.jpg","https://lh5.googleusercontent.com/-0BDXkYmckbo/URquhKFW84I/AAAAAAAAAbs/ogQtHCTk2JQ/s160-c/Closed%252520Door.jpg","https://lh3.googleusercontent.com/-PyggXXZRykM/URquh-kVvoI/AAAAAAAAAbs/hFtDwhtrHHQ/s160-c/Colorado%252520River%252520Sunset.jpg","https://lh3.googleusercontent.com/-ZAs4dNZtALc/URquikvOCWI/AAAAAAAAAbs/DXz4h3dll1Y/s160-c/Colors%252520of%252520Autumn.jpg","https://lh4.googleusercontent.com/-GztnWEIiMz8/URqukVCU7bI/AAAAAAAAAbs/jo2Hjv6MZ6M/s160-c/Countryside.jpg","https://lh4.googleusercontent.com/-bEg9EZ9QoiM/URquklz3FGI/AAAAAAAAAbs/UUuv8Ac2BaE/s160-c/Death%252520Valley%252520-%252520Dunes.jpg","https://lh6.googleusercontent.com/-ijQJ8W68tEE/URqulGkvFEI/AAAAAAAAAbs/zPXvIwi_rFw/s160-c/Delicate%252520Arch.jpg","https://lh5.googleusercontent.com/-Oh8mMy2ieng/URqullDwehI/AAAAAAAAAbs/TbdeEfsaIZY/s160-c/Despair.jpg","https://lh5.googleusercontent.com/-gl0y4UiAOlk/URqumC_KjBI/AAAAAAAAAbs/PM1eT7dn4oo/s160-c/Eagle%252520Fall%252520Sunrise.jpg","https://lh3.googleusercontent.com/-hYYHd2_vXPQ/URqumtJa9eI/AAAAAAAAAbs/wAalXVkbSh0/s160-c/Electric%252520Storm.jpg","https://lh5.googleusercontent.com/-PyY_yiyjPTo/URqunUOhHFI/AAAAAAAAAbs/azZoULNuJXc/s160-c/False%252520Kiva.jpg","https://lh6.googleusercontent.com/-PYvLVdvXywk/URqunwd8hfI/AAAAAAAAAbs/qiMwgkFvf6I/s160-c/Fitzgerald%252520Streaks.jpg","https://lh4.googleusercontent.com/-KIR_UobIIqY/URquoCZ9SlI/AAAAAAAAAbs/Y4d4q8sXu4c/s160-c/Foggy%252520Sunset.jpg","https://lh6.googleusercontent.com/-9lzOk_OWZH0/URquoo4xYoI/AAAAAAAAAbs/AwgzHtNVCwU/s160-c/Frantic.jpg","https://lh3.googleusercontent.com/-0X3JNaKaz48/URqupH78wpI/AAAAAAAAAbs/lHXxu_zbH8s/s160-c/Golden%252520Gate%252520Afternoon.jpg","https://lh6.googleusercontent.com/-95sb5ag7ABc/URqupl95RDI/AAAAAAAAAbs/g73R20iVTRA/s160-c/Golden%252520Gate%252520Fog.jpg","https://lh3.googleusercontent.com/-JB9v6rtgHhk/URqup21F-zI/AAAAAAAAAbs/64Fb8qMZWXk/s160-c/Golden%252520Grass.jpg","https://lh4.googleusercontent.com/-EIBGfnuLtII/URquqVHwaRI/AAAAAAAAAbs/FA4McV2u8VE/s160-c/Grand%252520Teton.jpg","https://lh4.googleusercontent.com/-WoMxZvmN9nY/URquq1v2AoI/AAAAAAAAAbs/grj5uMhL6NA/s160-c/Grass%252520Closeup.jpg","https://lh3.googleusercontent.com/-6hZiEHXx64Q/URqurxvNdqI/AAAAAAAAAbs/kWMXM3o5OVI/s160-c/Green%252520Grass.jpg","https://lh5.googleusercontent.com/-6LVb9OXtQ60/URquteBFuKI/AAAAAAAAAbs/4F4kRgecwFs/s160-c/Hanging%252520Leaf.jpg","https://lh4.googleusercontent.com/-zAvf__52ONk/URqutT_IuxI/AAAAAAAAAbs/D_bcuc0thoU/s160-c/Highway%2525201.jpg","https://lh6.googleusercontent.com/-H4SrUg615rA/URquuL27fXI/AAAAAAAAAbs/4aEqJfiMsOU/s160-c/Horseshoe%252520Bend%252520Sunset.jpg","https://lh4.googleusercontent.com/-JhFi4fb_Pqw/URquuX-QXbI/AAAAAAAAAbs/IXpYUxuweYM/s160-c/Horseshoe%252520Bend.jpg","https://lh5.googleusercontent.com/-UGgssvFRJ7g/URquueyJzGI/AAAAAAAAAbs/yYIBlLT0toM/s160-c/Into%252520the%252520Blue.jpg","https://lh3.googleusercontent.com/-CH7KoupI7uI/URquu0FF__I/AAAAAAAAAbs/R7GDmI7v_G0/s160-c/Jelly%252520Fish%2525202.jpg","https://lh4.googleusercontent.com/-pwuuw6yhg8U/URquvPxR3FI/AAAAAAAAAbs/VNGk6f-tsGE/s160-c/Jelly%252520Fish%2525203.jpg","https://lh5.googleusercontent.com/-GoUQVw1fnFw/URquv6xbC0I/AAAAAAAAAbs/zEUVTQQ43Zc/s160-c/Kauai.jpg","https://lh6.googleusercontent.com/-8QdYYQEpYjw/URquwvdh88I/AAAAAAAAAbs/cktDy-ysfHo/s160-c/Kyoto%252520Sunset.jpg","https://lh4.googleusercontent.com/-vPeekyDjOE0/URquwzJ28qI/AAAAAAAAAbs/qxcyXULsZrg/s160-c/Lake%252520Tahoe%252520Colors.jpg","https://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}ImageDownLoader类，异步下载的核心类，保存图片到手机缓存，将图片加入LruCache中等等
package com.example.asyncimageloader;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
public class ImageDownLoader {
/**
* 缓存Image的类，当存储Image的大小大于LruCache设定的值，系统自动释放内存
*/
private LruCache<String,Bitmap> mMemoryCache;
/**
* 操作文件相关类对象的引用
*/
private FileUtils fileUtils;
/**
* 下载Image的线程池
*/
private ExecutorService mImageThreadPool = null;
public ImageDownLoader(Context context){
//获取系统分配给每个应用程序的最大内存，每个应用系统分配32M
int maxMemory = (int) Runtime.getRuntime().maxMemory();
int mCacheSize = maxMemory / 8;
//给LruCache分配1/8 4M
mMemoryCache = new LruCache<String,Bitmap>(mCacheSize){
//必须重写此方法，来测量Bitmap的大小
@Override
protected int sizeOf(String key,Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
};
fileUtils = new FileUtils(context);
}
/**
* 获取线程池的方法，因为涉及到并发的问题，我们加上同步锁
* @return
*/
public ExecutorService getThreadPool(){
if(mImageThreadPool == null){
synchronized(ExecutorService.class){
if(mImageThreadPool == null){
//为了下载图片更加的流畅，我们用了2个线程来下载图片
mImageThreadPool = Executors.newFixedThreadPool(2);
}
}
}
return mImageThreadPool;
}
/**
* 添加Bitmap到内存缓存
* @param key
* @param bitmap
*/
public void addBitmapToMemoryCache(String key,Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null && bitmap != null) {
mMemoryCache.put(key,bitmap);
}
}
/**
* 从内存缓存中获取一个Bitmap
* @param key
* @return
*/
public Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
/**
* 先从内存缓存中获取Bitmap,如果没有就从SD卡或者手机缓存中获取，SD卡或者手机缓存
* 没有就去下载
* @param url
* @param listener
* @return
*/
public Bitmap downloadImage(final String url,final onImageLoaderListener listener){
//替换Url中非字母和非数字的字符，这里比较重要，因为我们用Url作为文件名，比如我们的Url
//是Http://xiaanming/abc.jpg;用这个作为图片名称，系统会认为xiaanming为一个目录，
//我们没有创建此目录保存文件就会报错
final String subUrl = url.replaceAll("[^\\w]","");
Bitmap bitmap = showCacheBitmap(subUrl);
if(bitmap != null){
return bitmap;
}else{
final Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
listener.onImageLoader((Bitmap)msg.obj,url);
}
};
getThreadPool().execute(new Runnable() {
@Override
public void run() {
Bitmap bitmap = getBitmapFormUrl(url);
Message msg = handler.obtainMessage();
msg.obj = bitmap;
handler.sendMessage(msg);
try {
//保存在SD卡或者手机目录
fileUtils.savaBitmap(subUrl,bitmap);
} catch (IOException e) {
e.printStackTrace();
}
//将Bitmap 加入内存缓存
addBitmapToMemoryCache(subUrl,bitmap);
}
});
}
return null;
}
/**
* 获取Bitmap,内存中没有就去手机或者sd卡中获取，这一步在getView中会调用，比较关键的一步
* @param url
* @return
*/
public Bitmap showCacheBitmap(String url){
if(getBitmapFromMemCache(url) != null){
return getBitmapFromMemCache(url);
}else if(fileUtils.isFileExists(url) && fileUtils.getFileSize(url) != 0){
//从SD卡获取手机里面获取Bitmap
Bitmap bitmap = fileUtils.getBitmap(url);
//将Bitmap 加入内存缓存
addBitmapToMemoryCache(url,bitmap);
return bitmap;
}
return null;
}
/**
* 从Url中获取Bitmap
* @param url
* @return
*/
private Bitmap getBitmapFormUrl(String url) {
Bitmap bitmap = null;
HttpURLConnection con = null;
try {
URL mImageUrl = new URL(url);
con = (HttpURLConnection) mImageUrl.openConnection();
con.setConnectTimeout(10 * 1000);
con.setReadTimeout(10 * 1000);
con.setDoInput(true);
con.setDoOutput(true);
bitmap = BitmapFactory.decodeStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
} finally {
if (con != null) {
con.disconnect();
}
}
return bitmap;
}
/**
* 取消正在下载的任务
*/
public synchronized void cancelTask() {
if(mImageThreadPool != null){
mImageThreadPool.shutdownNow();
mImageThreadPool = null;
}
}
/**
* 异步下载图片的回调接口
* @author len
*
*/
public interface onImageLoaderListener{
void onImageLoader(Bitmap bitmap,String url);
}
}ImageDownLoader中有几个方法比较重要:
1.首先我们需要重写sizeOf(String key,Bitmap value)来计算图片的大小，默认返回图片的数量
2.downloadImage(final String url,final onImageLoaderListener listener)先去LruCache查看Image,没有再去手机缓存中查看，在没有则开启线程下载，这里我们提供了一个回调接口，回调方法中我们将Bitmap和图片Url作为参数，String subUrl = url.replaceAll(“[^\w]”,“”) 我在代码中注释写的比较清楚
3.showCacheBitmap(String url)方法，此方法在Adapter中的getView()当中调用，如果getView()中不调用此方法试试你就知道效果了
ImageAdapter GridView的适配器类，主要是GridView滑动的时候取消下载任务，静止的时候去下载当前显示的item的图片，其他也没什么不同了
package com.example.asyncimageloader;
import android.content.Context;
import android.graphics.Bitmap;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import com.example.asyncimageloader.ImageDownLoader.onImageLoaderListener;
public class ImageAdapter extends BaseAdapter implements OnScrollListener{
/**
* 上下文对象的引用
*/
private Context context;
/**
* Image Url的数组
*/
private String [] imageThumbUrls;
/**
* GridView对象的应用
*/
private GridView mGridView;
/**
* Image 下载器
*/
private ImageDownLoader mImageDownLoader;
/**
* 记录是否刚打开程序，用于解决进入程序不滚动屏幕，不会下载图片的问题。
* 参考http://blog.csdn.net/guolin_blog/article/details/9526203#comments
*/
private boolean isFirstEnter = true;
/**
* 一屏中第一个item的位置
*/
private int mFirstVisibleItem;
/**
* 一屏中所有item的个数
*/
private int mVisibleItemCount;
public ImageAdapter(Context context,GridView mGridView,String [] imageThumbUrls){
this.context = context;
this.mGridView = mGridView;
this.imageThumbUrls = imageThumbUrls;
mImageDownLoader = new ImageDownLoader(context);
mGridView.setOnScrollListener(this);
}
@Override
public void onScrollStateChanged(AbsListView view,int scrollState) {
//仅当GridView静止时才去下载图片，GridView滑动时取消所有正在下载的任务
if(scrollState == AbsListView.OnScrollListener.SCROLL_STATE_IDLE){
showImage(mFirstVisibleItem,mVisibleItemCount);
}else{
cancelTask();
}
}
/**
* GridView滚动的时候调用的方法，刚开始显示GridView也会调用此方法
*/
@Override
public void onScroll(AbsListView view,int firstVisibleItem,int visibleItemCount,int totalItemCount) {
mFirstVisibleItem = firstVisibleItem;
mVisibleItemCount = visibleItemCount;
// 因此在这里为首次进入程序开启下载任务。
if(isFirstEnter && visibleItemCount > 0){
showImage(mFirstVisibleItem,mVisibleItemCount);
isFirstEnter = false;
}
}
@Override
public int getCount() {
return imageThumbUrls.length;
}
@Override
public Object getItem(int position) {
return imageThumbUrls[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position,View convertView,ViewGroup parent) {
ImageView mImageView;
final String mImageUrl = imageThumbUrls[position];
if(convertView == null){
mImageView = new ImageView(context);
}else{
mImageView = (ImageView) convertView;
}
mImageView.setLayoutParams(new GridView.LayoutParams(150,150));
mImageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
//给ImageView设置Tag,这里已经是司空见惯了
mImageView.setTag(mImageUrl);
/*******************************去掉下面这几行试试是什么效果****************************/
Bitmap bitmap = mImageDownLoader.showCacheBitmap(mImageUrl.replaceAll("[^\\w]",""));
if(bitmap != null){
mImageView.setImageBitmap(bitmap);
}else{
mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));
}
/**********************************************************************************/
return mImageView;
}
/**
* 显示当前屏幕的图片，先会去查找LruCache，LruCache没有就去sd卡或者手机目录查找，在没有就开启线程去下载
* @param firstVisibleItem
* @param visibleItemCount
*/
private void showImage(int firstVisibleItem,int visibleItemCount){
Bitmap bitmap = null;
for(int i=firstVisibleItem; i<firstVisibleItem + visibleItemCount; i++){
String mImageUrl = imageThumbUrls[i];
final ImageView mImageView = (ImageView) mGridView.findViewWithTag(mImageUrl);
bitmap = mImageDownLoader.downloadImage(mImageUrl,new onImageLoaderListener() {
@Override
public void onImageLoader(Bitmap bitmap,String url) {
if(mImageView != null && bitmap != null){
mImageView.setImageBitmap(bitmap);
}
}
});
//if(bitmap != null){
// mImageView.setImageBitmap(bitmap);
//}else{
// mImageView.setImageDrawable(context.getResources().getDrawable(R.drawable.ic_empty));
//}
}
}
/**
* 取消下载任务
*/
public void cancelTask(){
mImageDownLoader.cancelTask();
}
}MainActivity 里面一个GridView，然后提供一个系统菜单来删除手机上的缓存图片，直接上代码，比较简单所以里面也没有注释
package com.example.asyncimageloader;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.GridView;
import android.widget.Toast;
public class MainActivity extends Activity {
private GridView mGridView;
private String [] imageThumbUrls = Images.imageThumbUrls;
private ImageAdapter mImageAdapter;
private FileUtils fileUtils;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fileUtils = new FileUtils(this);
mGridView = (GridView) findViewById(R.id.gridView);
mImageAdapter = new ImageAdapter(this,mGridView,imageThumbUrls);
mGridView.setAdapter(mImageAdapter);
}
@Override
protected void onDestroy() {
mImageAdapter.cancelTask();
super.onDestroy();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
menu.add("删除手机中图片缓存");
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case 0:
fileUtils.deleteFile();
Toast.makeText(getApplication(),"清空缓存成功",Toast.LENGTH_SHORT).show();
break;
}
return super.onOptionsItemSelected(item);
}
}MainActivity的布局文件
<RelativeLayout 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"
tools:context=".MainActivity" >
<GridView
android:id="@+id/gridView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:stretchMode="columnWidth"
android:columnWidth="90dip"
android:verticalSpacing="10dip"
android:horizontalSpacing="10dip"
android:cacheColorHint="@android:color/transparent"
android:numColumns="auto_fit" >
</GridView>
</RelativeLayout>因为有网络操作和对sd卡的操作，所以我们必须加上相对应的权限
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 好了，代码就全部介绍完了，我们运行下程序看看效果
可以看到，滚动照片墙，会异步加载图片到相应的ImageView上。随着加载图片的增多，会释放掉一些之前加载过的图片，你多滚动几次就可以看得出了。另外为了能让大家明显看出图片的释放情况，我在这个程序中没有使用本地缓存，所有被释放掉的图片再次显示需要从网络上再下载一遍。在实际的项目中配合适当的本地缓存效果会更好。
打开DDMS，我们可以发现，由于有LruCache帮我们管理图片缓存，不管如何滚动照片墙，程序内存始终会保持在一个合理的范围内。
推荐阅读：
Android照片墙应用实现，再多的图片也不怕崩溃
Android高效加载大图、多图解决方案，有效避免程序OOM