列表视图在翻转和滚动时显示错误的视图几秒钟[英] Listview showing wrong view for a few seconds while flinging and scrolling

问题描述

The system seems to be recycling views until it loads the correct position's view in my listview, resulting in duplicated images and text for a few seconds. Can anyone help?

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    View v = convertView;
    Log.d("position",""+position);

    if(v==null){
        LayoutInflater inflater = LayoutInflater.from(mContext);
        v = inflater.inflate(R.layout.layout_appinfo, null);

        holder = new ViewHolder();
        holder.ivAppIcon = (ImageView)v.findViewById(R.id.ivIconApp);
        holder.tvAppName = (TextView)v.findViewById(R.id.tvNameApp);
        holder.progress = (ProgressBar)v.findViewById(R.id.progress_spinner);
        v.setTag(holder);
    } else {
        holder = (ViewHolder) v.getTag();
    }
    holder.ivAppIcon.setImageDrawable(null);
    holder.tvAppName.setText(null);
    holder.progress.setVisibility(View.VISIBLE);
    holder.ivAppIcon.setVisibility(View.GONE);

    // Using an AsyncTask to load the slow images in a background thread
    new AsyncTask<ViewHolder, Void, Drawable>() {
        private ViewHolder v;
        private ResolveInfo entry = (ResolveInfo) mListAppInfo.get(position);

        @Override
        protected Drawable doInBackground(ViewHolder... params) {
            v = params[0];
            return entry.loadIcon(mPackManager);
        }

        @Override
        protected void onPostExecute(Drawable result) {
            super.onPostExecute(result);
            // If this item hasn't been recycled already, hide the
            // progress and set and show the image
            v.progress.setVisibility(View.GONE);
            v.ivAppIcon.setVisibility(View.VISIBLE);
            v.ivAppIcon.setImageDrawable(result);
            v.tvAppName.setText(entry.loadLabel(mPackManager));
        }
    }.execute(holder);
    return v;
}

static class ViewHolder {
      TextView tvAppName;
      ImageView ivAppIcon;
      ProgressBar progress;
      //int position;
}

It is almost as if the position is being set wrong for a few seconds.

推荐答案

You can let the ViewHolder hold a reference to the AsyncTask. When convertView != null, you can call cancel() on the AsyncTask held by the ViewHolder since you know the image it is loading will not be correct for this new row. In doInBackgrond() and onPostExecute(), first check if(!isCancelled()) before doing anything.

static class ViewHolder {
    TextView tvAppName;
    ImageView ivAppIcon;
    ProgressBar progress;
    AsyncTask task;
}

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        /* inflate new view, make new ViewHolder, etc. */
        ...
    } else {
        holder = (ViewHolder) convertView.getTag();
        holder.task.cancel();
    }

    // always make a new AsyncTask, they cannot be reused
    holder.task = new AsyncTask ...
    holder.execute(...);
    ...
}

其他推荐答案

Android's developer documentation has a great section on this:

http://developer.android.com/training/displaying-bitmaps/process-bitmap.html

This issue, as stated above, is that your AsyncTask is keeping a hard reference to a view that's already been recycled.

其他推荐答案

You could set the current items image view to a standard loading image or nothing right away when you provide the view via the adapter. This will always "reset" the image, while it is loaded on your async task. This is probably the best approach to keep the performance benefits of the recycled views. Same goes for the text.