我正在使用 JSON 来解析在线 xml 文档以及两种延迟图像加载的方法。以下是我的源代码、解释和我的问题：
解释：
方法一：
使用AsyncTask和线imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);适配器内部。
方法二：
Not use AsyncTask并使用 try-catch 块的其余部分而不是该行imageLoader.DisplayImage((String)jsonImageText.get("imageLink"), activity, imageView);
问题：
方法一：
图像显示在模拟器上，加载速度相当快，但无法在手机或平板电脑上显示。
方法二：
图像在所有模拟器和真实设备上都显示，但加载和滚动非常慢。
有什么办法可以解决这两种方法中的任何一个或什至同时解决这两个方法吗？
这是返回 ListView 的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();
}
}
