Android - ListView scrollig too slow

I have a ListView that has one image and two lines of texts for each element (organized by a RelativeLayout). It works ok, but it's too slow and I know where the problem comes from!

This is the getView() method for the custom adapter that I'm using:

public View getView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                convertView = mLayoutInflater.inflate(R.layout.list_view_item, parent, false);
                mViewHolder = new ViewHolder();
                mViewHolder.cover = (ImageView) convertView.findViewById(R.id.app_icon);
                mViewHolder.title = (TextView) convertView.findViewById(R.id.selection);
                mViewHolder.description = (TextView) convertView.findViewById(R.id.app_short_description);
                convertView.setTag(mViewHolder);
            } else {
                mViewHolder = (ViewHolder) convertView.getTag();
            }

            // Here is the origin of the issue ! 
            final Feed currentFeed = getItem(position);
            mViewHolder.title.setText(currentFeed.getTitle());
            mViewHolder.description.setText(currentFeed.getDescription());

            try {
                if(currentFeed.getThumbnailUrl() != null) {
                     downloadThumbnail(mViewHolder.cover, currentFeed.getThumbnailUrl());
                }
            } catch(Exception e) {
                e.printStackTrace();
            }

            return convertView;
}

private static class ViewHolder {
        TextView title;
        TextView description;
        ImageView cover;
}

So I have done some manual benchmarking and it appears that allocating an instance of Feed is the source of this slowness:

final Feed currentFeed = getItem(position);

I know this because I have written another version of this to compare the two:

// Here is the origin of the issue ! 
            //final Feed currentFeed = getItem(position);
            mViewHolder.title.setText("Title");
            mViewHolder.description.setText("Description");

            try {
            if(currentFeed.getThumbnailUrl() != null) {
                 downloadThumbnail(mViewHolder.cover, "some url");
            }
        } catch(Exception e) {
            e.printStackTrace();
        }

This one was way smoother (even with the downloadThumbnail() method working).

I also precise that there are only 15 items on my ListView.

I know that allocating objects is very expensive because of garbage collection but I can't any other way to do it!

Any idea?

Thanks!

EDIT

Don't mind too much about the downloadThumbnail() method, it already does some caching. And actually even without any picture, it's still slow.

回答1:

When user scrolls the list, getView gets called on the adapter. Make sure that you dont do same things repeatedly, for example generating thumbnail. If number of items is limited (for example video content), then you can create all views and keep it ready for get view. Otherwise you may have to implement cacheing.

Below code shows an adapter and listView implementation, where in all listviews are created and stored in memory. Since this is meant for video browsing, memory does not pose any issue. (limited number of content, max 100)

Video List Adapter

import java.util.ArrayList;
import java.util.Formatter;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;

import android.content.ContentResolver;
import android.content.Context;
import android.content.res.Resources;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.provider.MediaStore;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.LinearLayout.LayoutParams;

public class VideoListAdapter extends BaseAdapter {
    private Context mContext = null;
    private HashMap<String, VideoListItem> mHashedItems = new HashMap<String, VideoListItem>(); 
    private static final String TAG = "VideoListAdapter";

    public static final int VIDEO_CONTENT_ID       = 0;
    public static final int VIDEO_CONTENT_TITLE    = 1;
    public static final int VIDEO_CONTENT_DURATION = 2;
    public static final int VIDEO_CONTENT_RESOLUTION = 3;
    public static final int VIDEO_CONTENT_MIME = 4;

    private Cursor mCursorForVideoList = null;
    private ContentResolver mContentResolver = null;
    private int mListCount = 0;

    VideoListAdapter(Context context, ContentResolver cr) {
        mContext         = context;
        mContentResolver = cr;
        Log.i(TAG, "In the Constructor");

        mCursorForVideoList = 
            mContentResolver.query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, 
                                  new String[] { MediaStore.MediaColumns._ID, 
                                                 MediaStore.MediaColumns.TITLE, 
                                                 MediaStore.Video.VideoColumns.DURATION,
                                                 MediaStore.Video.VideoColumns.RESOLUTION
                                               }, 
                                  null, 
                                  null,  
                                  null);
        mListCount = mCursorForVideoList.getCount();
    }

    @Override
    public int getCount() {
        return mListCount;
    }

    @Override
    public Object getItem(int arg0) {
        return getVideoListItem(arg0);
    }

    @Override
    public long getItemId(int position) {
        //Log.i(TAG, "position : " + position);
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        //Log.i(TAG, "GetView :: Position : " + position);
        return getVideoListItem(position);
    }

    private VideoListItem getVideoListItem(int position)
    {
        //Log.i(TAG, "getVideoListItem :: Position : " + position);
        String key = Integer.toString(position);
        VideoListItem item = mHashedItems.get(key);
        if(item == null)
        {
            //Log.i(TAG, "New getVideoListItem :: Position : " + position);
            mCursorForVideoList.moveToPosition(position);
            mHashedItems.put(key, new VideoListItem(mContext, mContentResolver, mCursorForVideoList));
        }
        return mHashedItems.get(key);
    }

};

Video List View

import java.util.Formatter;
import java.util.Locale;

import android.content.ContentResolver;
import android.content.Context;
import android.content.res.Resources;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.graphics.Typeface;
import android.provider.MediaStore;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TableLayout;
import android.widget.TextView;
import android.widget.LinearLayout.LayoutParams;

class VideoListItem extends LinearLayout
{
    private static final String TAG = "VideoListAdapter";

    private ImageView mThumbnail = null;
    private TextView mDuration   = null;
    private TextView mTitle      = null;
    private TextView mResolution = null;

    private LayoutInflater mLayoutFactory = null;

    private long mContentId = 0;

    public VideoListItem(Context context, ContentResolver cr, Cursor cursor) {
        super(context);
        LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
        params.setMargins(10, 10, 10, 10);

        mLayoutFactory = LayoutInflater.from(context);
        View thisView = mLayoutFactory.inflate(R.layout.videolistitem, null);
        addView(thisView);

        mThumbnail  = (ImageView) findViewById(R.id.thumbnail); 
        mDuration   = (TextView)  findViewById(R.id.DDuration);
        mTitle      = (TextView)  findViewById(R.id.DTitle);
        mResolution = (TextView)  findViewById(R.id.DResolution);

        mThumbnail.setLayoutParams(new LinearLayout.LayoutParams(144, 144));

        Resources r = this.getResources();
        Bitmap bMap = MediaStore.Video.Thumbnails.getThumbnail(cr, cursor.getLong(VideoListAdapter.VIDEO_CONTENT_ID), MediaStore.Video.Thumbnails.MINI_KIND, null);
        if(bMap != null)
        {
            mThumbnail.setImageBitmap(Bitmap.createScaledBitmap(bMap, 128, 128, true)); 
        }
        else
        {
            mThumbnail.setImageDrawable(r.getDrawable(R.drawable.error));
        }
        mThumbnail.setPadding(16, 16, 16, 16);
        mTitle.setText(cursor.getString(VideoListAdapter.VIDEO_CONTENT_TITLE));
        mTitle.setSingleLine();
        mTitle.setTextColor(Color.GREEN);

        mResolution.setText(cursor.getString(VideoListAdapter.VIDEO_CONTENT_RESOLUTION));
        mResolution.setSingleLine();
        mResolution.setTextColor(Color.RED);

        mDuration.setText(stringForTime(cursor.getInt(VideoListAdapter.VIDEO_CONTENT_DURATION)));
        mDuration.setSingleLine();
        mDuration.setTextColor(Color.CYAN);

        mContentId = cursor.getLong(VideoListAdapter.VIDEO_CONTENT_ID);
    }

    public long getContentId()
    {
        return mContentId;
    }

    private StringBuilder mFormatBuilder = null;
    private Formatter mFormatter = null;

    private String stringForTime(int timeMs) {
        int totalSeconds = timeMs / 1000;

        mFormatBuilder = new StringBuilder();
        mFormatter = new Formatter(mFormatBuilder, Locale.getDefault());

        int seconds = totalSeconds % 60;
        int minutes = (totalSeconds / 60) % 60;
        int hours   = totalSeconds / 3600;

        mFormatBuilder.setLength(0);
        if (hours > 0) {
            return mFormatter.format("%d:%02d:%02d", hours, minutes, seconds).toString();
        } else {
            return mFormatter.format("%02d:%02d", minutes, seconds).toString();
        }
    }

};

Shash

回答2:

Don't allocate or store the Feed object in your View holder and instead only store the position (position). When you need to reference the object then grab the reference index from the ViewHolder and act accordingly.

Edit
Of course I missed that you're using the object later on... You might also create a number of minimal, static methods for your Feed object that only return specific things, such as the title, etc. Then call these methods in your getView method to set the UI elements without full creation of the Feed itself.