Android 是否用图像永久填充ListView?
我目前正在开发一个应用程序,其中我有一个列表视图。此listview由联机从XML文件获取的文本和图像填充。但是,无论何时滚动,屏幕上当前没有的任何内容都会重新加载并重新计算位图的大小,以显示在listview中。这会导致滚动不那么流畅和烦人。我如何让我的活动用图像填充listview并加载一次以保持在那里 图像加载器:Android 是否用图像永久填充ListView?,android,image,listview,caching,android-bitmap,Android,Image,Listview,Caching,Android Bitmap,我目前正在开发一个应用程序,其中我有一个列表视图。此listview由联机从XML文件获取的文本和图像填充。但是,无论何时滚动,屏幕上当前没有的任何内容都会重新加载并重新计算位图的大小,以显示在listview中。这会导致滚动不那么流畅和烦人。我如何让我的活动用图像填充listview并加载一次以保持在那里 图像加载器: public class ImageLoader { MemoryCache memoryCache = new MemoryCache(); FileCache fileC
public class ImageLoader {
MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
int size;
int placeholderpic;
public ImageLoader(Context context, int size, int placeholderpic) {
fileCache = new FileCache(context);
executorService = Executors.newFixedThreadPool(5);
this.size = size;
this.placeholderpic = placeholderpic;
}
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(placeholderpic);
}
}
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 = size;
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(placeholderpic);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
公共类ImageLoader{
MemoryCache MemoryCache=新的MemoryCache();
文件缓存文件缓存;
private Map ImageView=Collections.synchronizedMap(新的WeakHashMap());
执行服务执行服务;
整数大小;
int占位符pic;
公共图像加载器(上下文上下文、整型大小、整型占位符){
fileCache=新的fileCache(上下文);
executorService=Executors.newFixedThreadPool(5);
这个。大小=大小;
this.placeholder pic=placeholder pic;
}
public void displayImage(字符串url,ImageView){
put(imageView,url);
位图位图=memoryCache.get(url);
if(位图!=null)
设置图像位图(位图);
否则{
队列照片(url、imageView);
setImageResource(占位符pic);
}
}
私有void队列照片(字符串url,ImageView){
PhotoToLoad p=新的PhotoToLoad(url,imageView);
executorService.submit(新的PhotoLoader(p));
}
私有位图getBitmap(字符串url){
文件f=fileCache.getFile(url);
//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;
URL imageUrl=新URL(URL);
HttpURLConnection conn=(HttpURLConnection)imageUrl.openConnection();
连接设置连接超时(30000);
连接设置读取超时(30000);
conn.setInstanceFollowRedirects(真);
InputStream is=conn.getInputStream();
OutputStream os=新文件OutputStream(f);
Utils.CopyStream(is,os);
os.close();
位图=解码文件(f);
返回位图;
}捕获(可丢弃的ex){
例如printStackTrace();
if(ex instanceof OutOfMemoryError)
memoryCache.clear();
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。
所需最终整型尺寸=尺寸;
内部宽度=o.向外宽度,高度=o.向外高度;
int标度=1;
while(true){
如果(宽度\u tmp/2<所需尺寸| |高度\u tmp/2<所需尺寸)
打破
宽度_tmp/=2;
高度_tmp/=2;
比例*=2;
}
//用inSampleSize解码
BitmapFactory.Options o2=新的BitmapFactory.Options();
o2.inSampleSize=刻度;
返回BitmapFactory.decodeStream(新文件输入流(f),null,o2);
}catch(filenotfound异常){}
返回null;
}
//队列的任务
私有类光电负载{
公共字符串url;
公共影像视图;
公共PhotoToLoad(字符串u,图像视图i){
url=u;
imageView=i;
}
}
类photoloader实现可运行{
光电负载光电负载;
PhotoLoader(PhotoToLoad PhotoToLoad){
this.photoToLoad=photoToLoad;
}
@凌驾
公开募捐{
if(图像视图重用(光电加载))
返回;
位图bmp=getBitmap(photoLoad.url);
memoryCache.put(photoload.url,bmp);
if(图像视图重用(光电加载))
返回;
BitmapDisplayer bd=新的BitmapDisplayer(bmp,photoToLoad);
活动a=(活动)photoToLoad.imageView.getContext();
a、 runOnUiThread(bd);
}
}
布尔图像视图(PhotoToLoad PhotoToLoad){
String tag=imageViews.get(photoload.imageView);
if(tag==null | |!tag.equals(photoload.url))
返回true;
返回false;
}
//用于在UI线程中显示位图
类BitmapDisplayer实现可运行{
位图;
光电负载光电负载;
公共位图显示器(位图b、PhotoToLoad p){
位图=b;光电负载=p;
}
公开募捐{
if(图像视图重用(光电加载))
返回;
if(位图!=null)
photoToLoad.imageView.setImageBitmap(位图);
其他的
photoToLoad.imageView.setImageResource(占位符pic);
}
}
公共void clearCache(){
memoryCache.clear();
fileCache.clear();
}
ListView适配器:
public class LazyNewsAdapter extends BaseAdapter {
private Activity activity;
private ArrayList<News> listData;
private LayoutInflater inflater = null;
public LazyNewsAdapter(Activity activity, ArrayList<News> listData) {
this.activity = activity;
this.listData = listData;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
public int getCount() {
return listData.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
News newsItem = listData.get(position);
View view = convertView;
if(convertView == null)
view = inflater.inflate(R.layout.news_cell, null);
TextView newsTitle = (TextView) view.findViewById(R.id.newsTitle);
TextView newsDate = (TextView) view.findViewById(R.id.newsDate);
ImageView image = (ImageView) view.findViewById(R.id.newsImage);
newsTitle.setText(newsItem.getNewsTitle());
newsDate.setText(newsItem.getNewsDate());
String url = newsItem.getNewsImageUrl();
ImageLoader imageLoader = new ImageLoader(activity, 600, R.drawable.placeholder);
imageLoader.displayImage(url, image);
return view;
}
公共类LazyNewsAdapter扩展了BaseAdapter{
私人活动;
私有数组列表数据;
专用充气机=空;
公共LazyNewsAdapter(活动,ArrayList listData){
这个。活动=活动;
this.listData=listData;
充气器=(LayoutInflater)activity.getSystemService(Context.LAYOUT\u充气器\u SERVICE);
}
public int getCount(){
返回listData.size();
}
公共对象getItem(int位置){
返回位置;
}
公共长getItemId(int位置){
返回位置;
}
公共视图getView(int位置、视图转换视图、视图组父视图){
News newsItem=listData.get(位置);
视图=转换视图;
if(convertView==null)
视图=充气机。充气(R.layout.news\u单元格,空);
TextView newsTitle=(TextView)view.findViewById(R.id.newsTitle);
TextView newsDate=(TextView)view.findViewById(R.id.newsDate);
ImageView image=(ImageView)view.findViewById(R.id.newsImage);
newsttitle.setText(newsItem.getnewsttitle());
newsDate.setText(newsItem.getNewsDate());
字符串url=newsItem.getNewsImageUrl();
图像加载
ImageLoader imageLoader = new ImageLoader(activity, 600, R.drawable.placeholder);