我试图显示设备上直接从媒体存储请求数据的歌曲列表。我使用一个RecyclerView
和一个使用CursorAdapter
从mediastore获取数据的适配器。
当调用适配器的onBindViewHolder
时,请求被传递给bindView
的CursorAdapter
函数,所有可视元素都被设置。
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);
}
}
问题部分是图像加载,由两部分组成:
使用从
Cursor
获得的唱片ID,我需要使用ContentResolver
获取唱片集艺术文件路径使用文件路径将图像加载到
ImageView
中这两段需要在后台完成,否则滚动将变得非常滞后。在
bindView
函数中,我调用了一个AsyncTask
函数来完成任务,但问题是,在快速滚动时,会详细说明几个图像请求,这就是结果:从代码中可以看到,我试图取消特定
ImageView
上挂起的毕加索请求,但这还不够。这个问题能解决吗? 最佳答案
我通过在ViewHolder
中添加一个包含相对于该项的AsyncTask
的字段来解决这个问题。在bindView
函数中,我首先设置AsyncTask.cancel(true)
,在任务中,我在使用isCancelled()
应用检索到的图像之前检查了Picasso.with(...).load(...)
。这本身就解决了闪烁问题。
绑定视图
if(holder.downloadImageTask != null)
holder.downloadImageTask.cancel(true);
holder.downloadImageTask = (DownloadImageTask) new DownloadImageTask(mediaStoreHelper, context, holder.imgArt).execute(holder.album_id);
异步任务
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,这还将从回收项目中移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);
}
这个解决方案使我认为问题在于,在从mediastore检索图像和实际将图像应用到毕加索的
AsyncTask
之间的ImageView
内部的时间间隔。