Question

我想通过AsyncTask将一些图像下载到SD卡，并在完成后在列表视图中显示它们。下载开始时会显示一个进度条，当它停止时会显示在SD卡上下载的图像。

我看到很多关于延迟加载的帖子，但我想要的是在显示图像之前显示进度条，我想存储在SD卡上。

波纹管代码几乎可以正常工作，但问题是它在下载图像时始终没有在正确的项目上显示正确的图片。我正在使用适配器中的波纹管：

  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);
            }
....

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

首先，您需要在异步任务类上使用progress方法。 Link。然后为你的方法在顶部创建一个变量来传递不同的序列让我们说5,4,3,2,1。当它开始时它会变为5并递减到1然后应用程序将发布并执行你正在进行的任何gui交互。

Android如何使用AsyncTask将图像下载到SD卡，并在右侧项目的listview上完成显示？

1 个答案: