我找到了Fedor的代码here并将其实现到我的项目中。唯一的区别是我的应用程序没有列表视图，而是我从服务器一次访问1个图像。当活动启动时，我调用“DisplayImage（...）”来显示第一张图片。然后有2个按钮（上一个/下一个），点击它们时，它们调用“DisplayImage（...）”。
它工作正常一段时间，但后来我得到一个Out of Memory错误。在他的代码的顶部，他评论您可能想要使用SoftReference。我假设这会解决我的问题，对吗？我玩了一下但是当我尝试修改它以使用SoftReference时，图像永远不会加载。我之前从未使用过SoftReference所以我认为我只是缺少一些东西。我如何修改该代码（ImageLoader）来修复我的OOM错误？在浏览图片时是否有更好的缓存方式？
更新 如果您不想查看源中的其他文件，请输入以下代码。
package com.fedorvlasov.lazylist;
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 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.stub;
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);
Utils.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 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);
Object tag=photoToLoad.imageView.getTag();
if(tag!=null && ((String)tag).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();
}
}
在我尝试实现SoftReference之后，这是同一个类。我不认为我做得对，因为加载后这不会在屏幕上显示图片。
package com.mycompany.myapp;
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.lang.ref.SoftReference;
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 ImageLoader {
//the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
private HashMap<String, SoftReference<Bitmap>> cache=new HashMap<String, SoftReference<Bitmap>>();
private File cacheDir;
public ImageLoader(Context context){
//Make the background thread 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(),"MyApp/Temp");
else
cacheDir=context.getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();
}
final int stub_id = R.drawable.loading;
public void DisplayImage(String url, Activity activity, ImageView imageView)
{
if(cache.containsKey(url)){
imageView.setImageBitmap(null);
System.gc();
imageView.setImageBitmap(cache.get(url).get());
} else {
queuePhoto(url, activity, imageView);
imageView.setImageBitmap(null);
System.gc();
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 SoftReference<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
SoftReference<Bitmap> b = decodeFile(f);
if(b!=null)
return b;
//from web
try {
SoftReference<Bitmap> bitmap=null;
InputStream is=new URL(url).openStream();
OutputStream os = new FileOutputStream(f);
Utils.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 SoftReference<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=1024;
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 cache.get(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();
}
SoftReference<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);
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
{
SoftReference<Bitmap> bitmap;
ImageView imageView;
public BitmapDisplayer(SoftReference<Bitmap> bmp, ImageView i){bitmap=bmp;imageView=i;}
public void run()
{
if(bitmap!=null){
imageView.setImageBitmap(null);
System.gc();
imageView.setImageBitmap(bitmap.get());
} else {
imageView.setImageBitmap(null);
System.gc();
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();
}
}
答案 0 :(得分：7)
通常，您的内存中图像缓存声明应如下所示：
private static HashMap<String, SoftReference<Bitmap>> cache =
new HashMap<String, SoftReference<Bitmap>>();
请注意，您的OOM问题可能不一定与您的位图缓存有关。始终确保在Activity的onDestroy方法中或在管理它的任何其他类的最终化中停止/中断由图像加载器生成的线程。
将Eclipse Memory Analyzer工具与DDMS结合使用来分析应用程序的内存使用情况：http://www.eclipse.org/mat/
答案 1 :(得分：0)
要修复我的OOM使用Lazy Loader，我每次创建或销毁页面时都会手动调用垃圾收集（System.gc（）;）（可能会做一个或另一个会很好），因为Android并不总是如此尽可能多地调用它，并使用Fedor的clearCache方法：
if (ImageLoader.getImageCache() != null)
ImageLoader.clearCache();
函数在那里，但除非你使用它，否则永远不会被任何东西调用。我在使用Lazy Load的第二个活动的onCreate中执行此操作。你也可以这样做：
@Override
public void onLowMemory() {
super.onLowMemory();
ImageLoader.clearCache();
}
这似乎永远不会被我召唤，但是你的图像有多大，你可能需要它。还要考虑缩小图像，除非你有理由将它们保持得如此之大。
答案 2 :(得分：0)
我面临同样的问题，我使用SoftReference作为位图和网址，但似乎Dalvik VM很快收回SoftReference，我的ListView图像一直闪烁然后我试了inPurgeable {{ 1}}我越过= true，我的OutOfMemoryException图片没有闪烁。
答案 3 :(得分：0)
考虑回收分配给位图图像的内存
bitmap.recyle（）; 位图= NULL;
当你不再需要位图图像时，调用此函数，这将释放一些内存
答案 4 :(得分：-1)
您应该在Android 2.1或更低版本中更改以下行。
cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"MyApp/Temp");
到这个
cacheDir = new File(context.getCacheDir(), "MyApp/Temp");