无法使用自定义列表适配器在Android中缓存图像文件

Question

我为我当前的应用程序使用自定义列表视图，除了图像缓存外，一切都很好。图像不是缓存。任何人请帮我在我的代码中找到我的错误。

这是我的代码：

DownloadImage中的参数URL是完整的图片网址。

private Bitmap DownloadImage(String URL)
    {       
        Bitmap bitmap = null;
        InputStream in = null;       
        try {
            in = OpenHttpConnection(URL);
            bitmap = BitmapFactory.decodeStream(in);            

            /*Write to Cache*/
            String[] imageName = URL.split("/");
            String imageFile = imageName[imageName.length-1];
            File file = new File(context.getCacheDir(), imageFile);
            file.createNewFile();

            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            bitmap.compress(CompressFormat.JPEG, 100 , bos);
            byte[] bitmapdata = bos.toByteArray();
            FileOutputStream fos = new FileOutputStream(file);
            fos.write(bitmapdata);  
            fos.flush();
            fos.close();
            bos.close();
            /*Write to Cache*/

            in.close();
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
            bitmap = null;
        }
        return bitmap;               
    }

代码OpenHttpConnection：

private InputStream OpenHttpConnection(String urlString)
    throws IOException
    {
        InputStream in = null;
        int response = -1;

        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();

        if (!(conn instanceof HttpURLConnection))                    
            throw new IOException("Not an HTTP connection");

        try{
            HttpURLConnection httpConn = (HttpURLConnection) conn;
            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();

            response = httpConn.getResponseCode();                
            if (response == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();                                
            }                    
        }
        catch (Exception ex)
        {
            throw new IOException("Error connecting");
        }
        return in;    
    }