java - ProgressBar - 不在 AsyncTask 中更新

Question

您好，我刚刚有一个简短的问题，为什么我的进度条没有更新。我将在下面添加评论以演示哪些有效，哪些无效。

据我所知，它应该可以工作，因为它是在异步任务中更新的。

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    View view = convertView;
    if (!(data.get(position) instanceof TemporarySongInfomation)) {
        SongViewHolder holder;
        view = inflater.inflate(R.layout.music_list_format, null);
        holder = new SongViewHolder();
        holder.timesplayed = (TextView) view.findViewById(R.id.textView7);
        holder.artist = (TextView) view.findViewById(R.id.textView6);
        holder.title = (TextView) view.findViewById(R.id.textView5);
        holder.imagebutton = (ImageButton) view.findViewById(R.id.playbutton);
        holder.source = (TextView) view.findViewById(R.id.textView8);
        tempValue = (SongInfomation) data.get(position);
        String songName = tempValue.getName();
        holder.imagebutton.setBackgroundResource(R.drawable.playbutton1);
        holder.source.setText(tempValue.getVideoid());
        holder.title.setText(songName.length() > 45 ? songName.substring(0, 38) + "..." : songName);
        holder.timesplayed.setText("" + tempValue.getTimesplayed());
        holder.artist.setText(tempValue.getArtist());
        swipeDetector = new SwipeDetector();
        view.setOnClickListener(new SongListOnItemClickListener(position));
        view.setOnTouchListener(swipeDetector);
        holder.imagebutton.setOnClickListener(new OnPlayButtonClickListener(position));
    } else {
        TemporarySongViewHolder holder;
        view = inflater.inflate(R.layout.music_list_process_format, null);
        holder = new TemporarySongViewHolder();
        holder.artist = (TextView) view.findViewById(R.id.artisttemp);
        holder.bar = (ProgressBar) view.findViewById(R.id.ppbar);
        holder.title = (TextView) view.findViewById(R.id.titletemp);
        holder.source = (TextView) view.findViewById(R.id.sourcetemp);
        tempValue1 = (TemporarySongInfomation) data.get(position);
        String songName = tempValue1.getName();
        holder.source.setText(tempValue1.getVideoid());
        holder.title.setText(songName.length() > 45 ? songName.substring(0, 38) + "..." : songName);
        holder.artist.setText(tempValue1.getArtist());
        holder.bar.setMax(100);
// the below line starts the task!
        new UpdateProgressBar(holder.bar, tempValue1).execute();

    }

    return view;
}

private class UpdateProgressBar extends AsyncTask<Void, Void, Void> {
    private TemporarySongInfomation songinfo;
    private ProgressBar progress;

    UpdateProgressBar(ProgressBar bar, TemporarySongInfomation tp) {
        progress = bar;
        songinfo = tp;
    }

    @Override
    protected Void doInBackground(Void... params) {
        while (!songinfo.isCompleted()) {
            System.out.println("going " + (int) songinfo.getProgress());
// the above line prints different values for songinfo.getProgress()
            progress.setProgress((int) songinfo.getProgress());
            publishProgress();
            System.out.println("Progress "+progress.getProgress());
// the above line only prints "Progress 0"
// and obviously the ui doesnt update.
            try {
                Thread.sleep(500);
            } catch (Exception e) {

            }
        }
        return null;
    }
}

Answer 1

publishProgress(进度...) 调用 onProgressUpdate(进度...)

onProgressUpdate(Progress...) invoked on the UI thread after a call to publishProgress(Progress...). The timing of the execution is undefined. This method is used to display any form of progress in the user interface while the background computation is still executing. For instance, it can be used to animate a progress bar or show logs in a text field.

所以基本上您需要通过 onProgressUpdate 方法更新 UI 线程。

举个例子:

private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
     protected Long doInBackground(URL... urls) {
         int count = urls.length;
         long totalSize = 0;
         for (int i = 0; i < count; i++) {
             totalSize += Downloader.downloadFile(urls[i]);
             publishProgress((int) ((i / (float) count) * 100));
             // Escape early if cancel() is called
             if (isCancelled()) break;
         }
         return totalSize;
     }

     protected void onProgressUpdate(Integer... progress) {
         setProgressPercent(progress[0]);
     }

     protected void onPostExecute(Long result) {
         showDialog("Downloaded " + result + " bytes");
     }
 }