我使用JSON来解析在线xml文档，还使用2种方法来加载延迟图像。以下是我的源代码，解释和我的问题：
说明：
方法1：
在适配器内使用AsyncTask和行imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);。
方法2：
不使用AsyncTask并使用try-catch块的其余部分而不是行imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);
问题：
方法1：
图像显示在模拟器上，加载非常快，但无法在手机或平板电脑上显示。
方法2：
图像显示在所有模拟器和真实设备上，但加载和滚动速度非常慢。
有没有办法解决这两种方法中的任何一种，甚至两种方法？
这是返回ListView行视图的列表适配器：
public class RssListAdapter extends ArrayAdapter<JSONObject> {
public ImageLoader imageLoader;
public RssListAdapter(Activity activity, List<JSONObject> imageAndTexts) {
super(activity, 0, imageAndTexts);
imageLoader=new ImageLoader(activity.getApplicationContext());
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Activity activity = (Activity) getContext();
LayoutInflater inflater = activity.getLayoutInflater();
// Inflate the views from XML
View rowView = inflater.inflate(R.layout.image_text_layout, null);
JSONObject jsonImageText = getItem(position);
TextView textView = (TextView) rowView.findViewById(R.id.job_text);
ImageView imageView = (ImageView) rowView.findViewById(R.id.feed_image);
try {
if (jsonImageText.get("imageLink") != null){
System.out.println("XXXX Link found!");
String url = (String) jsonImageText.get("imageLink");
URL feedImage= new URL(url);
HttpURLConnection conn= (HttpURLConnection)feedImage.openConnection();
InputStream is = conn.getInputStream();
Bitmap img = BitmapFactory.decodeStream(is);
imageView.setImageBitmap(img);
//imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);
}
Spanned text = (Spanned)jsonImageText.get("text");
textView.setText(text);
}
catch (MalformedURLException e) {
textView.setText("JSON Exception");
}
catch (IOException e) {
textView.setText("JSON Exception");
}
catch (JSONException e) {
textView.setText("JSON Exception");
}
return rowView;
}
}
这是ImageLoader类：
public class ImageLoader {
MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
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);
fileCache=new FileCache(context);
}
final int stub_id=R.drawable.icon;
public void DisplayImage(String url, Activity activity, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null)
imageView.setImageBitmap(bitmap);
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)
{
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);
InputStream is=conn.getInputStream();
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);
memoryCache.put(photoToLoad.url, bmp);
String tag=imageViews.get(photoToLoad.imageView);
if(tag!=null && 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() {
memoryCache.clear();
fileCache.clear();
}
}
答案 0 :(得分：2)
您可以尝试使用aquery安卓库来获取延迟加载图片和listview ...下面的代码可以帮助您..... download library from here
AQuery aq = new AQuery(mContext);
aq.id(R.id.image1).image("http://data.whicdn.com/images/63995806/original.jpg");