Question

我试图在设备上找到直接从MediaStore请求数据的歌曲列表。我使用RecyclerView和使用CursorAdapter的适配器从MediaStore获取数据。当调用适配器onBindViewHolder时，请求将传递给bindView CursorAdapter函数，所有可视元素都已设置。

public class ListRecyclerAdapter3 extends RecyclerView.Adapter<ListRecyclerAdapter3.SongViewHolder> {

    // PATCH: Because RecyclerView.Adapter in its current form doesn't natively support
    // cursors, we "wrap" a CursorAdapter that will do all teh job
    // for us
    public MediaStoreHelper mediaStoreHelper;
    CustomCursorAdapter mCursorAdapter;
    Context mContext;


    public class SongViewHolder extends RecyclerView.ViewHolder {

        public TextView textItemTitle;
        public TextView textItemSub;
        public ImageView imgArt;

        public int position;
        public String album_id;
        public String path_art;
        public String path_file;

        public SongViewHolder(View v) {
            super(v);
            textItemTitle = (TextView) v.findViewById(R.id.textItemTitle);
            textItemSub = (TextView) v.findViewById(R.id.textItemSub);
            imgArt = (ImageView) v.findViewById(R.id.imgArt);
        }
    }

    private class CustomCursorAdapter extends CursorAdapter {

        public CustomCursorAdapter(Context context, Cursor c, int flags) {
            super(context, c, flags);
        }

        @Override
        public View newView(final Context context, Cursor cursor, ViewGroup parent) {

            View v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.song_item, parent, false);

            final SongViewHolder holder = new SongViewHolder(v);

            v.setTag(holder);

            return v;
        }

        @Override
        public void bindView(View view, Context context, Cursor cursor) {
            SongViewHolder holder = (SongViewHolder) view.getTag();

            holder.position = cursor.getPosition();

            holder.textItemTitle.setText(cursor.getString(cursor.getColumnIndex("title")));
            holder.textItemSub.setText(cursor.getString(cursor.getColumnIndex("artist")));

            holder.album_id = cursor.getString(cursor.getColumnIndex("album_id"));
            holder.path_file = cursor.getString(cursor.getColumnIndex("_data"));

            Picasso.with(holder.imgArt.getContext())
                    .cancelRequest(holder.imgArt);
            holder.imgArt.setImageDrawable(null);

            new DownloadImageTask(mediaStoreHelper, context, holder.imgArt).execute(holder.album_id);
        }

    }

    private class DownloadImageTask extends AsyncTask<String, String, String> {

        private MediaStoreHelper mediaStoreHelper;
        private ImageView imageView;
        private Context context;

        public DownloadImageTask(MediaStoreHelper mediaStoreHelper, Context context, ImageView imageView)
        {
            this.mediaStoreHelper = mediaStoreHelper;
            this.context = context;
            this.imageView = imageView;
        }
        @Override
        protected String doInBackground(String... ids) {
            return mediaStoreHelper.getAlbumArtPath(ids[0]);
        }

        protected void onPostExecute(String result) {
            Picasso.with(context)
                    .load(new File(result))
                    .placeholder(R.drawable.ic_music)
                    .fit()
                    .into(imageView);
        }
    }

    @Override
    public void onBindViewHolder(SongViewHolder holder, int position) {
        // Passing the binding operation to cursor loader
        mCursorAdapter.getCursor().moveToPosition(position);
        mCursorAdapter.bindView(holder.itemView, mContext, mCursorAdapter.getCursor());
    }

    @Override
    public SongViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // Passing the inflater job to the cursor-adapter
        View v = mCursorAdapter.newView(mContext, mCursorAdapter.getCursor(), parent);
        return new SongViewHolder(v);
    }
}

有问题的部分是图像加载，由两部分组成：

使用 albumId 我来自Cursor，我需要使用ContentResolver来获取专辑封面文件路径
使用文件路径将图像加载到ImageView

这两个段落需要在后台完成，否则滚动会变得非常迟钝。在bindView函数中，我调用AsyncTask来完成工作，但问题是，在快速滚动时，会详细说明几个图像请求，结果就是这样：

正如您从代码中看到的那样，我尝试取消Picasso对特定ImageView的待审请求，但这还不够。这个问题能解决吗？

Answer 1

我通过在ViewHolder中添加一个相对于该项目的AsyncTask字段来解决问题。在bindView函数中，我设置了AsyncTask.cancel(true)，在使用isCancelled()应用检索到的图像之前，我在任务内部进行了检查Picasso.with(...).load(...)。这本身就解决了闪烁问题。

<强> bindView

if(holder.downloadImageTask != null)
      holder.downloadImageTask.cancel(true);

      holder.downloadImageTask = (DownloadImageTask) new DownloadImageTask(mediaStoreHelper, context, holder.imgArt).execute(holder.album_id);

<强>的AsyncTask

private class DownloadImageTask extends AsyncTask<String, String, String> {

        private MediaStoreHelper mediaStoreHelper;
        private ImageView imageView;
        private Context context;

        public DownloadImageTask(MediaStoreHelper mediaStoreHelper, Context context, ImageView imageView)
        {
            this.mediaStoreHelper = mediaStoreHelper;
            this.context = context;
            this.imageView = imageView;
        }
        @Override
        protected String doInBackground(String... ids) {
            return mediaStoreHelper.getAlbumArtPath(ids[0]);
        }

        protected void onPostExecute(String result) {
            if(!isCancelled())
                Picasso.with(context)
                        .load(new File(result))
                        .placeholder(R.drawable.ic_music)
                        .fit()
                        .into(imageView);
        }
    }

为了完整起见，这也会从回收物品中删除图像并设置占位符。

@Override
public void onViewRecycled(SongViewHolder holder) {
    super.onViewRecycled(holder);
    Picasso.with(holder.itemView.getContext())
            .cancelRequest(holder.imgArt);
    Picasso.with(holder.itemView.getContext())
            .load(R.drawable.ic_music)
            .fit()
            .into(holder.imgArt);
}

这个解决方案让我觉得问题是从MediaStore图像检索到图像实际应用到毕加索AsyncTask之间ImageView内部的时间量。

Answer 2

评论这些

闪烁正在发生，因为对于单个项目，bind不会被调用一次，因此它会一次又一次地调用单行，并且每次都设置为null并且还在其上设置视图。产生闪烁。

 Picasso.with(holder.imgArt.getContext())
                    .cancelRequest(holder.imgArt);
            holder.imgArt.setImageDrawable(null);

Answer 3

您正在使用的异步任务完全错误。

首先，您永远不应该执行匿名异步任务。

其次，摆脱适配器中的这个异步任务，因为它似乎导致了问题。

获取适配器的数据，然后显示它。

顺便说一句，终止毕加索最好这样做：

       @Override public void onViewRecycled(VH holder) {
            super.onViewRecycled(holder);
            Picasso.with(holder.itemView.getContext())
                   .cancelRequest(holder.getImageView());
        }

在RecyclerView中滚动时图像闪烁

3 个答案: