Android编程使用缓存优化ListView的方法

public class MyReadAdapter extends BaseAdapter{
 private List<CollectionEntry> entrys;
 public MyReadAdapter(CollectionFeed feeds) {
  entrys = feeds.getEntries();
 }
 public int getCount() {
  return entrys.size();
 }
 public Object getItem(int position) {
  return entrys.get(position);
 }
 public long getItemId(int position) {
  return position;
 }
 public View getView(int position, View convertView, ViewGroup parent) {
  View view = infalter.inflate(R.layout.myread_item, null);
  final ImageView iv = (ImageView) view.findViewById(R.id.book_img);
  //获取数据实体
  CollectionEntry ce = entrys.get(position);
  //获取图片地址
  String iconurl = ce.getSubjectEntry().getLink("image", null).getHref();
  int start = iconurl.lastIndexOf("/");
  int end = iconurl.length();
  final String iconname = iconurl.substring(start, end);
  //Environment.getExternalStorageDirectory()这个是sd卡目录
  File file = new File(Environment.getExternalStorageDirectory(),iconname);
  //获取sd卡缓存
  if(file.exists()){
   iv.setImageURI(Uri.fromFile(file));
   Log.i(TAG,"使用sd卡图片");
  }else{
   new LoadImageAsynTask(new ImageTaskCallback() {
   // 图片获取之后
   public void onImageLoaded(Bitmap bitmap) {
    if(bitmap!=null){
    iv.setImageBitmap(bitmap);
    //把图片存到sd卡上
    if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
     try {
      File file = new File(Environment.getExternalStorageDirectory(),iconname);
      FileOutputStream fos = new FileOutputStream(file);
      bitmap.compress(CompressFormat.JPEG, 100, fos);
     } catch (Exception e) {
      e.printStackTrace();
     }
    }
    }else{
     iv.setImageResource(R.drawable.book);
    }
   }
   //图片获取之前
   public void beforeImageLoaded() {
    iv.setImageResource(R.drawable.book);
   }
  }).execute(iconurl);
  }
  return view;
 }
}

Map<String,SoftReference<Bitmap>> map;
public class MyReadAdapter extends BaseAdapter{
 private List<CollectionEntry> entrys;
 public MyReadAdapter(CollectionFeed feeds) {
  entrys = feeds.getEntries();
 }
 public int getCount() {
  return entrys.size();
 }
 public Object getItem(int position) {
  return entrys.get(position);
 }
 public long getItemId(int position) {
  return position;
 }
 public View getView(int position, View convertView, ViewGroup parent) {
  View view = infalter.inflate(R.layout.myread_item, null);
  final ImageView iv = (ImageView) view.findViewById(R.id.book_img);
  //获取到数据的实体
  CollectionEntry ce = entrys.get(position);
  //获取到图片的Url
  String iconurl = ce.getSubjectEntry().getLink("image", null).getHref();
  int start = iconurl.lastIndexOf("/");
  int end = iconurl.length();
  final String iconname = iconurl.substring(start, end);
  //使用内存缓存
  if(map!=null && map.get(iconname)!=null){
   iv.setImageBitmap(map.get(iconname).get());
   Log.i(TAG,"使用内存缓存");
  }
  else{
  new LoadImageAsynTask(new ImageTaskCallback() {
   // 图片获取之后
   public void onImageLoaded(Bitmap bitmap) {
    if(bitmap!=null){
    iv.setImageBitmap(bitmap);
    //存放到内存中,
    //软引用类型的bitmap
    map.put(iconname, new SoftReference<Bitmap>(bitmap));
    }else{
     iv.setImageResource(R.drawable.book);
    }
   }
   //图片获取之前
   public void beforeImageLoaded() {
    iv.setImageResource(R.drawable.book);
   }
  }).execute(iconurl);
  }
  return view;
 }
}