问安卓doInBackground

EN

private class DownloadImageTask extends AsyncTask<URL, Integer, Bitmap> {
    // This class definition states that DownloadImageTask will take String
    // parameters, publish Integer progress updates, and return a Bitmap
    protected Bitmap doInBackground(URL... paths) {
        URL url;
        try {
            url = paths[0];
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();
            int length = connection.getContentLength();
            InputStream is = (InputStream) url.getContent();
            byte[] imageData = new byte[length];
            int buffersize = (int) Math.ceil(length / (double) 100);
            int downloaded = 0;
            int read;
            while (downloaded < length) {
                if (length < buffersize) {
                    read = is.read(imageData, downloaded, length);
                } else if ((length - downloaded) <= buffersize) {
                    read = is.read(imageData, downloaded, length
                            - downloaded);
                } else {
                    read = is.read(imageData, downloaded, buffersize);
                }
                downloaded += read;
                publishProgress((downloaded * 100) / length);
            }
            Bitmap bitmap = BitmapFactory.decodeByteArray(imageData, 0,
                    length);
            if (bitmap != null) {
                Log.i(TAG, "Bitmap created");
            } else {
                Log.i(TAG, "Bitmap not created");
            }
            is.close();
            return bitmap;
        } catch (MalformedURLException e) {
            Log.e(TAG, "Malformed exception: " + e.toString());
        } catch (IOException e) {
            Log.e(TAG, "IOException: " + e.toString());
        } catch (Exception e) {
            Log.e(TAG, "Exception: " + e.toString());
        }
        return null;

    }

    protected void onPostExecute(Bitmap result) {
        String name = ImageLink.substring(ImageLink
                .lastIndexOf("/") + 1);
        if (result != null) {
            hasExternalStoragePublicPicture(name);
            saveToSDCard(result, name);
            isImage = true;

        } else {
            isImage = false;

        }
    }
}