Android 使用延迟加载时在ListView中复制ImageView
我在列表视图中使用延迟加载。奇怪的是,屏幕上的第一行和最后一行似乎有相同的图像(屏幕上最后一行的图像) 屏幕)。 我使用以下类加载图像:Android 使用延迟加载时在ListView中复制ImageView,android,Android,我在列表视图中使用延迟加载。奇怪的是,屏幕上的第一行和最后一行似乎有相同的图像(屏幕上最后一行的图像) 屏幕)。 我使用以下类加载图像: public class ImageLoader { //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
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.default_user_pic;
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);
HeaderController.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++;
}
//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);
if(((String)photoToLoad.imageView.getTag()).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();
}
}
公共类ImageLoader{
//最简单的内存缓存实现。应该用SoftReference或BitmapOptions.Inpurgable(自1.6起)之类的东西来代替
私有HashMap缓存=新建HashMap();
私有文件cacheDir;
公共图像加载器(上下文){
//将后台设为低优先级。这样不会影响UI性能
photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);
//查找目录以保存缓存的图像
if(android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_-MOUNTED))
cacheDir=新文件(android.os.Environment.getExternalStorageDirectory(),“LazyList”);
其他的
cacheDir=context.getCacheDir();
如果(!cacheDir.exists())
cacheDir.mkdirs();
}
最终int stub\u id=R.drawable.default\u user\u pic;
public void DisplayImage(字符串url、活动活动、图像视图)
{
if(cache.containsKey(url))
setImageBitmap(cache.get(url));
其他的
{
队列照片(url、活动、图像视图);
setImageResource(存根id);
}
}
私有void queuePhoto(字符串url、活动活动、ImageView ImageView)
{
//此ImageView以前可能用于其他图像。因此队列中可能有一些旧任务。我们需要丢弃它们。
Photosque.Clean(imageView);
PhotoToLoad p=新的PhotoToLoad(url,imageView);
已同步(PhotoQueue.photosToLoad){
photoqueue.photoload.push(p);
photoqueue.phototoload.notifyAll();
}
//如果尚未启动,则启动线程
if(photoLoaderThread.getState()==Thread.State.NEW)
photoLoaderThread.start();
}
私有位图getBitmap(字符串url)
{
//我用hashcode识别图像。这不是一个完美的解决方案,适合演示。
String filename=String.valueOf(url.hashCode());
文件f=新文件(cacheDir,文件名);
//从SD缓存
位图b=解码文件(f);
如果(b!=null)
返回b;
//从网络
试一试{
位图=空;
InputStream is=新URL(URL).openStream();
OutputStream os=新文件OutputStream(f);
HeaderController.CopyStream(is,os);
os.close();
位图=解码文件(f);
返回位图;
}捕获(例外情况除外){
例如printStackTrace();
返回null;
}
}
//对图像进行解码和缩放以减少内存消耗
私有位图解码文件(文件f){
试一试{
//解码图像大小
BitmapFactory.Options o=新的BitmapFactory.Options();
o、 inJustDecodeBounds=true;
解码流(新的FileInputStream(f),null,o);
//找到正确的刻度值。它应该是2的幂。
所需的最终int_尺寸=70;
内部宽度=o.向外宽度,高度=o.向外高度;
int标度=1;
while(true){
if(width_tmp/2我强烈建议您使用该库。如果需要,我将提供示例。我也遇到了类似的问题。我通过将imageview设置为默认图片解决了这个问题
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(R.drawable.icon);
}
}
它不漂亮,但它解决了我的复制图像问题
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(R.drawable.icon);
}
}