android - for循环在异步任务的Doinbackground中不递增

Question

我正在使用 for 循环从 doInBackground 中的数组列表中读取图像 url，但循环不递增，只有第一个 url 正在加载和保存图像。这是代码:

class DownloadImageTask extends AsyncTask<Void, Void, Bitmap> {
    // This class definition states that DownloadImageTask will take String
    // parameters, publish Integer progress updates, and return a Bitmap
    @SuppressWarnings("unused")
    protected Bitmap doInBackground(Void... paths) {
        //URL url;
        try {
              for(int j=0; j<List.size();j++)
            {
                     reviewImageLink =List.get(j).get(TAG_Image);
                     URL     url = new URL(reviewImageLink);
                    // URL reviewImageURL;
                    String name = reviewImageLink.substring(reviewImageLink .lastIndexOf("/") + 1,reviewImageLink.length());
                        //try {

                            if (!hasExternalStoragePublicPicture(name)) {
                                isImage = false;
                                //new DownloadImageTask().execute();
                                Log.v("log_tag", "if");
                                isImage = true;
                                File sdImageMainDirectory = new File(Environment.getExternalStorageDirectory(), getResources().getString(R.string.directory));
                            //if(!sdImageMainDirectory.exists()){
                                sdImageMainDirectory.mkdirs();
                                File file = new File(sdImageMainDirectory, name);
                                Log.v("log_tag", "Directory created");}
                    //}
                    //  catch (MalformedURLException e) {
                        //  Log.v(TAG, e.toString());   }
              //  }

           // }//try 
           // catch (Exception e) {
               //     e.printStackTrace();}
            //url = new URL(List.get(j).get(TAG_Image));
            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;
                setProgress((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 = reviewImageLink.substring(reviewImageLink.lastIndexOf("/") + 1,reviewImageLink.length());
        if (result != null) {
            hasExternalStoragePublicPicture(name);
            saveToSDCard(result, name);
            isImage = true;

        } else {
            isImage = false;

        }
    }
}

Answer 1

List是一个接口(interface)，不能像List.size()那样使用。定义一个List子类型，比如ArrayList之类的。for循环没有错. 例如:

List<Integer> li = new ArrayList<Integer>();
li.add(10);
li.add(20)';
for(int i = 0; i <= li.size(); ++i) {
//your stuff
}