Android如何使用AsyncTask将图像下载到sdcard并在完成后显示在右侧项目的listview上？

Question

I want to download some images through AsyncTask to SDcard and on completion to show them on an listview. When the download starts an progress bar is shown, when it stops will show the image downloaded on sdcard.

I saw that are a lot of posts with lazy-load, but what i want is to show a progress bar before showing the image, and i want to be stored on sdcard.

The bellow code works almost ok, but the problem is that it doesnt show the right picture on the right item all the time when it is downloading the image. I am using the bellow in the adapter:

  public View getView(final int position, View convertView, ViewGroup parent) {
        final PooHolder holder; 
        if(convertView == null){
            convertView = inflater.inflate(R.layout.item_poo, null);
            holder = new PooHolder();
            holder.tvTime = (TextView)convertView.findViewById(R.id.tvTime);
            holder.tvMessage = (TextView)convertView.findViewById(R.id.tvMessage);
            holder.btnDislike = (ImageButton)convertView.findViewById(R.id.btnDislike);
            holder.btnLike = (ImageButton)convertView.findViewById(R.id.btnLike);
            holder.btnReport = (ImageButton)convertView.findViewById(R.id.btnReport);
            holder.bar = (ProgressBar)convertView.findViewById(R.id.progressBar1);
            holder.bar1 = (ProgressBar)convertView.findViewById(R.id.progressBar2);
            holder.bar2 = (ProgressBar)convertView.findViewById(R.id.progressBar3);
            holder.tvLikes = (TextView)convertView.findViewById(R.id.tvLikes);
            holder.tvComments = (TextView)convertView.findViewById(R.id.tvComments);
            holder.tvDislikes = (TextView)convertView.findViewById(R.id.tvDislike);
            holder.imgPoo = (ImageView)convertView.findViewById(R.id.imgPoo);
            convertView.setTag(holder);
        }else{
            holder = (PooHolder)convertView.getTag();
        }
        final Poo poo = list.get(position);
        String vote = poo.getVote();

        if(poo.getDrawablePath()!=null){
            if(!poos.get(position).isDownloadComplete()){
                Log.i(DEBUG, poo.getMessage());
                holder.bar2.setVisibility(View.VISIBLE);
                holder.imgPoo.setImageBitmap(BitmapFactory.decodeFile(poo.getDrawablePath()));
                holder.imgPoo.setVisibility(View.INVISIBLE);
                if(!poos.get(position).getDownloadState(Poo.DOWNLOAD_START)){
                    DownloadImageTask task = new DownloadImageTask(poo, holder.bar2, holder.imgPoo);
                    task.setOnDownloadListener(new OnDownloadListener(){
                        public void onDownloadStarted() {
                            poos.get(position).startDownload();
                        }
                        public void onDownloadFinished(final Bitmap bmp) {
                            poos.get(position).stopDownload();
                        }
                    });
                    task.execute(poo.getImagePath());
                }
            }else{
                holder.bar2.setVisibility(View.INVISIBLE);
                holder.imgPoo.setVisibility(View.VISIBLE);
                holder.imgPoo.setImageBitmap(BitmapFactory.decodeFile(poo.getDrawablePath()));
                }
            }else{
                holder.bar2.setVisibility(View.INVISIBLE);
                holder.imgPoo.setVisibility(View.VISIBLE);
                holder.imgPoo.setImageResource(R.drawable.icon);
            }
....

The DownloadImageTask.java:

public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
    private final String DEBUG = "DownloadImageTask";
    private String url;
    private String imagePath;
    private OnDownloadListener listener;
    private Bitmap bmp;
    private ProgressBar bar;
    private ImageView img;
    private Poo poo;

    public DownloadImageTask(Poo poo, ProgressBar bar, ImageView img) {
        this.img = img;
        this.bar = bar;
        this.poo = poo;
    }

    public void onPreExecute(){
        super.onPreExecute();
        listener.onDownloadStarted();
        bar.setVisibility(View.VISIBLE);
        img.setImageBitmap(BitmapFactory.decodeFile(poo.getDrawablePath()));
        img.setVisibility(View.INVISIBLE);
    }

    public void setOnDownloadListener(OnDownloadListener listener){
        this.listener = listener;
    }

    @Override
    // Actual download method, run in the task thread
    protected Bitmap doInBackground(String... params) {
        this.imagePath = poo.getImagePath();
         // params comes from the execute() call: params[0] is the url.
        if(imagePath != null && !imagePath.isEmpty()){
            String file = imagePath.substring(imagePath.lastIndexOf("/") + 1, imagePath.length());
            return BoopoohooUtils.downloadImage(params[0], file);
        }else{
            return null;
        }
    }

    @Override
    // Once the image is downloaded, associates it to the imageView
    protected void onPostExecute(Bitmap bitmap) {
        Log.i(DEBUG, "bitmap " + bitmap);
        bar.setVisibility(View.INVISIBLE);
        img.startAnimation(BoopoohooUtils.fadeIn());
        img.setVisibility(View.VISIBLE);
        img.setImageBitmap(bitmap);
        listener.onDownloadFinished(bitmap);
    }
}

Answer 1

So to start you will need to use the progress method on the async task class. Link . Then for your method on the top create a variable for passing through different sequence let's say 5,4,3,2,1. When it starts it goes by 5 and decrements to 1 then application will go to post and do whatever gui interactions you are doing.