ListView图片异步加载与缓存策略

1,图片缓存用一个LinkedHashmap<String,SoftReference<Bitmap>> , 再存到本地. 需要时先判断map中有没有, 没有找本地文件, 再没有重新下载. 

2,当getView中异步加载图片的时候, convert不需要重用, 转而用set来保存生成的view

3,getview方法内不要做获取数据的处理, getView就是用来get view的

4,客户端不管如何优化,如果返回的都是大图片的话,仍然会OOM. 有些时候需要客户端增加字段,判断该字段还返回不同大小的图片.

private String getBitmapName(String imageUrl){
        String[] str = imageUrl.split("/");
        return str[str.length-2]+str[str.length-1]+"xxx";
    }
    public void loadBitmap(final String imageUrl, final ImageView imageview) {
        final Handler handler = new Handler() {
            public void handleMessage(Message msg) {
                imageview.setImageBitmap((Bitmap) msg.obj);
            };
        };
        
        final String bitmapName = getBitmapName(imageUrl);
        File localJPG = new File(localFolderName+bitmapName);
//        Log.v("0712 ", "获得到的图片名"+bitmapName);
        if (drawableMap.containsKey(imageUrl+"22")) {
            Log.e("0712 ", "直接用内存池的图片");
            SoftReference<Bitmap> softReference = drawableMap.get(imageUrl);
            Bitmap bitmap = softReference.get();
            if (bitmap != null) {
                // Message msg = handler.obtainMessage(0, bitmap);
                // handler.sendMessage(msg);
                imageview.setImageBitmap(bitmap);
            }
        } 
//        else if(localJPG.exists()){
            else if(false){
            Log.e("0712 ", "去找SD卡中的图片");
            BitmapDrawable drawable = (BitmapDrawable) BitmapDrawable.createFromPath(localFolderName+bitmapName);
            imageview.setImageDrawable(drawable);
        }
        else {
        
            Log.e("0712", "本地没有找到图片");
            imageview.setImageDrawable(null);
            File cacheDir = new File(localFolderName);
            // File[] cacheFiles = cacheDir.listFiles();
            // int i = 0;
            // if (cacheFiles != null) {
            // int count = cacheFiles.length;
            // for (; i < count; i++) // todo
            // {
            // Log.d("0712", "在循环找图片");
            // if (bitmapName.equals(cacheFiles[i].getName())) {
            // break;
            // }
            // }
            // // if (i < count) {
            // // Message msg = handler.obtainMessage(0,
            // // BitmapFactory.decodeFile(localFolderName +
            // // bitmapName));
            // // handler.sendMessage(msg);
            // // // imageview.setImageBitmap(
            // // // BitmapFactory.decodeFile(localFolderName +
            // // // imageUrl));
            // // }
            // }
            Thread thread = new Thread() {
                public void run() {
                    Log.e("0712", "new thread is running");

                    try {
                        URL fileURL = new URL(imageUrl);
                        HttpURLConnection conn;
                        conn = (HttpURLConnection) fileURL.openConnection();
                        InputStream bitmapIs = conn.getInputStream();
                        Bitmap bitmap = BitmapFactory.decodeStream(bitmapIs);
                        drawableMap.put(imageUrl, new SoftReference<Bitmap>(bitmap));
                        Message msg = handler.obtainMessage(0, bitmap);
                        handler.sendMessage(msg);
                        File dir = new File(localFolderName);
                        if (!dir.exists()) {
                            dir.mkdirs();
                        }

                        File bitmapFile = new File(localFolderName+ bitmapName);
                        if (!bitmapFile.exists()) {
                            try {
                                bitmapFile.createNewFile();
                            } catch (IOException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }
                        }

                        FileOutputStream fos;
                        try {
                            fos = new FileOutputStream(bitmapFile);
                            bitmap.compress(Bitmap.CompressFormat.JPEG, 80, fos);
                            fos.close();
                        } catch (FileNotFoundException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    } catch (IOException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    }
                };
            };
            MyThreadPoolManager.getInstance().startThread(imageUrl, thread);
        }

    }