
平台论坛博客文库

› 论坛 › 操作系统 › 移动操作系统 › android listview 滚动时异步加载图片的问题

android listview 滚动时异步加载图片的问题 [复制链接]

so_brave

家境小康

论坛徽章:: 0

电梯直达

1楼 [收藏(0)] [报告]

发表于 2011-12-05 15:56 |只看该作者 |倒序浏览

android listview 滚动时异步加载图片的问题

LoadImage.java

Java代码

package com.gowin.cach;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.graphics.Bitmap;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;
public class LoadImage {
private ExecutorService executorService; // 固定五个线程来
private ImageMemoryCache memoryCache;// 内存缓存
private ImageFileCache fileCache;// 文件缓存
private Map<String, ImageView> taskMap;// 存放任务
public LoadImage() {
executorService = Executors.newFixedThreadPool(10);
memoryCache = new ImageMemoryCache();
fileCache = new ImageFileCache();
taskMap = new HashMap<String, ImageView>();
}
public void addTask(String url, ImageView img) {
Bitmap bitmap=memoryCache.getBitmapFromCache(url);
if(bitmap!=null)
{
img.setImageBitmap(bitmap);
}else
{
synchronized (taskMap) {
taskMap.put(Integer.toString(img.hashCode()), img);
}
}
}
public void doTask() {
synchronized (taskMap) {
Collection<ImageView> con = taskMap.values();
for (ImageView i : con) {
if (i != null) {
if (i.getTag() != null) {
loadImage((String) i.getTag(), i);
}
}
}
taskMap.clear();
}
}
private void loadImage(String url, ImageView img) {
/*** 加入新的任务 ***/
executorService.submit(new TaskWithResult(new TaskHandler(url, img),
url));
}
/*** 获得一个图片,从三个地方获取,首先是内存缓存,然后是文件缓存,最后从网络获取 ***/
private Bitmap getBitmap(String url) {
// 从内存缓存中获取图片
Bitmap result;
result = memoryCache.getBitmapFromCache(url);
if (result == null) {
// 文件缓存中获取
result = fileCache.getImage(url);
if (result == null) {
// 从网络获取
result = ImageGetForHttp.downloadBitmap(url);
if (result != null) {
memoryCache.addBitmapToCache(url, result);
fileCache.saveBmpToSd(result, url);
}
} else {
// 添加到内存缓存
memoryCache.addBitmapToCache(url, result);
}
}
return result;
}
/*** 完成消息 ***/
private class TaskHandler extends Handler {
String url;
ImageView img;
public TaskHandler(String url, ImageView img) {
this.url = url;
this.img = img;
}
@Override
public void handleMessage(Message msg) {
/*** 查看imageview需要显示的图片是否被改变 ***/
if (img.getTag().equals(url)) {
if (msg.obj != null) {
Bitmap bitmap = (Bitmap) msg.obj;
img.setImageBitmap(bitmap);
}
}
}
}
/*** 子线程任务 ***/
private class TaskWithResult implements Callable<String> {
private String url;
private Handler handler;
public TaskWithResult(Handler handler, String url) {
this.url = url;
this.handler = handler;
}
@Override
public String call() throws Exception {
Message msg = new Message();
msg.obj = getBitmap(url);
if (msg.obj != null) {
handler.sendMessage(msg);
}
return url;
}
}
}
package com.gowin.cach;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import android.graphics.Bitmap;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;
public class LoadImage {
private ExecutorService executorService; // 固定五个线程来
private ImageMemoryCache memoryCache;// 内存缓存
private ImageFileCache fileCache;// 文件缓存
private Map<String, ImageView> taskMap;// 存放任务
public LoadImage() {
executorService = Executors.newFixedThreadPool(10);
memoryCache = new ImageMemoryCache();
fileCache = new ImageFileCache();
taskMap = new HashMap<String, ImageView>();
}
public void addTask(String url, ImageView img) {
Bitmap bitmap=memoryCache.getBitmapFromCache(url);
if(bitmap!=null)
{
img.setImageBitmap(bitmap);
}else
{
synchronized (taskMap) {
taskMap.put(Integer.toString(img.hashCode()), img);
}
}
}
public void doTask() {
synchronized (taskMap) {
Collection<ImageView> con = taskMap.values();
for (ImageView i : con) {
if (i != null) {
if (i.getTag() != null) {
loadImage((String) i.getTag(), i);
}
}
}
taskMap.clear();
}
}
private void loadImage(String url, ImageView img) {
/*** 加入新的任务 ***/
executorService.submit(new TaskWithResult(new TaskHandler(url, img),
url));
}
/*** 获得一个图片,从三个地方获取,首先是内存缓存,然后是文件缓存,最后从网络获取 ***/
private Bitmap getBitmap(String url) {
// 从内存缓存中获取图片
Bitmap result;
result = memoryCache.getBitmapFromCache(url);
if (result == null) {
// 文件缓存中获取
result = fileCache.getImage(url);
if (result == null) {
// 从网络获取
result = ImageGetForHttp.downloadBitmap(url);
if (result != null) {
memoryCache.addBitmapToCache(url, result);
fileCache.saveBmpToSd(result, url);
}
} else {
// 添加到内存缓存
memoryCache.addBitmapToCache(url, result);
}
}
return result;
}
/*** 完成消息 ***/
private class TaskHandler extends Handler {
String url;
ImageView img;
public TaskHandler(String url, ImageView img) {
this.url = url;
this.img = img;
}
@Override
public void handleMessage(Message msg) {
/*** 查看imageview需要显示的图片是否被改变 ***/
if (img.getTag().equals(url)) {
if (msg.obj != null) {
Bitmap bitmap = (Bitmap) msg.obj;
img.setImageBitmap(bitmap);
}
}
}
}
/*** 子线程任务 ***/
private class TaskWithResult implements Callable<String> {
private String url;
private Handler handler;
public TaskWithResult(Handler handler, String url) {
this.url = url;
this.handler = handler;
}
@Override
public String call() throws Exception {
Message msg = new Message();
msg.obj = getBitmap(url);
if (msg.obj != null) {
handler.sendMessage(msg);
}
return url;
}
}
}

复制代码

ImageMemoryCache.java (http://www.my400800.cn )

Java代码

package com.gowin.cach;
import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.concurrent.ConcurrentHashMap;
import android.graphics.Bitmap;
/****
*内存中的缓存
****/
public class ImageMemoryCache {
private static final int HARD_CACHE_CAPACITY = 30;
private HashMap<String, Bitmap> mHardBitmapCache ;
private final static ConcurrentHashMap<String, SoftReference<Bitmap>> mSoftBitmapCache =
new ConcurrentHashMap<String, SoftReference<Bitmap>>(HARD_CACHE_CAPACITY / 2);
public ImageMemoryCache()
{
mHardBitmapCache =
new LinkedHashMap<String, Bitmap>(HARD_CACHE_CAPACITY / 2, 0.75f, true) {
/**
*
*/
private static final long serialVersionUID = 1L;
@Override
protected boolean removeEldestEntry(LinkedHashMap.Entry<String, Bitmap> eldest) {
if (size() > HARD_CACHE_CAPACITY) {
// Entries push-out of hard reference cache are transferred to soft reference cache
mSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue()));
return true;
} else
return false;
}
};
}
/**
* 从缓存中获取图片
*/
public Bitmap getBitmapFromCache(String url) {
// 先从mHardBitmapCache缓存中获取
synchronized (mHardBitmapCache) {
final Bitmap bitmap =mHardBitmapCache.get(url);
if (bitmap != null) {
//如果找到的话，把元素移到linkedhashmap的最前面，从而保证在LRU算法中是最后被删除
mHardBitmapCache.remove(url);
mHardBitmapCache.put(url,bitmap);
return bitmap;
}
}
//如果mHardBitmapCache中找不到，到mSoftBitmapCache中找
SoftReference<Bitmap>bitmapReference = mSoftBitmapCache.get(url);
if (bitmapReference != null) {
final Bitmap bitmap =bitmapReference.get();
if (bitmap != null) {
//将图片移回硬缓存
mHardBitmapCache.put(url, bitmap);
mSoftBitmapCache.remove(url);
return bitmap;
} else {
mSoftBitmapCache.remove(url);
}
}
return null;
}
/***添加图片到缓存***/
public void addBitmapToCache(String url, Bitmap bitmap) {
if (bitmap != null) {
synchronized (mHardBitmapCache) {
mHardBitmapCache.put(url, bitmap);
}
}
}
}
package com.gowin.cach;
import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.concurrent.ConcurrentHashMap;
import android.graphics.Bitmap;
/****
*内存中的缓存
****/
public class ImageMemoryCache {
private static final int HARD_CACHE_CAPACITY = 30;
private HashMap<String, Bitmap> mHardBitmapCache ;
private final static ConcurrentHashMap<String, SoftReference<Bitmap>> mSoftBitmapCache =
new ConcurrentHashMap<String, SoftReference<Bitmap>>(HARD_CACHE_CAPACITY / 2);
public ImageMemoryCache()
{
mHardBitmapCache =
new LinkedHashMap<String, Bitmap>(HARD_CACHE_CAPACITY / 2, 0.75f, true) {
/**
*
*/
private static final long serialVersionUID = 1L;
@Override
protected boolean removeEldestEntry(LinkedHashMap.Entry<String, Bitmap> eldest) {
if (size() > HARD_CACHE_CAPACITY) {
// Entries push-out of hard reference cache are transferred to soft reference cache
mSoftBitmapCache.put(eldest.getKey(), new SoftReference<Bitmap>(eldest.getValue()));
return true;
} else
return false;
}
};
}
/**
* 从缓存中获取图片
*/
public Bitmap getBitmapFromCache(String url) {
// 先从mHardBitmapCache缓存中获取
synchronized (mHardBitmapCache) {
final Bitmap bitmap =mHardBitmapCache.get(url);
if (bitmap != null) {
//如果找到的话，把元素移到linkedhashmap的最前面，从而保证在LRU算法中是最后被删除
mHardBitmapCache.remove(url);
mHardBitmapCache.put(url,bitmap);
return bitmap;
}
}
//如果mHardBitmapCache中找不到，到mSoftBitmapCache中找
SoftReference<Bitmap>bitmapReference = mSoftBitmapCache.get(url);
if (bitmapReference != null) {
final Bitmap bitmap =bitmapReference.get();
if (bitmap != null) {
//将图片移回硬缓存
mHardBitmapCache.put(url, bitmap);
mSoftBitmapCache.remove(url);
return bitmap;
} else {
mSoftBitmapCache.remove(url);
}
}
return null;
}
/***添加图片到缓存***/
public void addBitmapToCache(String url, Bitmap bitmap) {
if (bitmap != null) {
synchronized (mHardBitmapCache) {
mHardBitmapCache.put(url, bitmap);
}
}
}
}