android - 在 android ListView 中滚动时滞后

Question

我有一个 ListView ，我必须在其中加载带有文本和标准图像的不同对象；但是在我提供给 ListView 的数组列表中，有些对象必须使用不同的“row.xml”加载。不知道有没有解释清楚，大概代码会说明一切:

这是我的适配器

    /**
 * 
 */


import java.util.List;

import com.larvalabs.svgandroid.SVG;
import com.larvalabs.svgandroid.SVGParser;



import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;


public class EventAdapter extends ArrayAdapter<EventEntry> {

    Typeface face;
    private static final Integer LIST_HEADER = 0;
    private static final Integer LIST_ITEM = 2;

    public EventAdapter(Context context, int textViewResourceId, List<EventEntry> objects) {
        super(context, textViewResourceId, objects);
        face=Typeface.createFromAsset(context.getAssets(),"fonts/arial.ttf");

    }



    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        return getViewOptimize(position, convertView, parent);
    }

    public View getViewOptimize(int position, View convertView, ViewGroup parent) {

        //piece of code for header items
        String headerText = getHeader(position);
        if(headerText != null) {

            View item = convertView;
            if(convertView == null || convertView.getTag() != LIST_HEADER) {

                item = LayoutInflater.from(getContext()).inflate(
                        R.layout.event_list_header, parent, false);
                item.setTag(LIST_HEADER);

            }

            TextView headerTextView = (TextView)item.findViewById(R.id.lv_list_hdr);
            headerTextView.setText(headerText);
            return item;
        }



        ViewHolder viewHolder = null;
        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) getContext()
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = inflater.inflate(R.layout.row_event, null);
            viewHolder = new ViewHolder();
            viewHolder.first = (TextView)convertView.findViewById(R.id.ev_tit_list);
            viewHolder.second = (ImageView)convertView.findViewById(R.id.ev_image_list);
            convertView.setTag(viewHolder);
        } else {
            try{
                viewHolder = (ViewHolder) convertView.getTag();
            }catch(ClassCastException e){
                LayoutInflater inflater = (LayoutInflater) getContext()
                        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = inflater.inflate(R.layout.row_event, null);
                viewHolder = new ViewHolder();
                viewHolder.first = (TextView)convertView.findViewById(R.id.ev_tit_list);
                viewHolder.second = (ImageView)convertView.findViewById(R.id.ev_image_list);
                convertView.setTag(viewHolder);
            }
        }
        EventEntry e = getItem(position);
        if (e.getEvento()!=null)
            return setEventItem(viewHolder, e.getEvento(), convertView);
        else 
            return setSagraItem(viewHolder, e.getSagra(), convertView);


    }

    public View setEventItem(ViewHolder viewHolder, Entry2ev e, View convertView){

        viewHolder.first.setTypeface(face, Typeface.BOLD );
        viewHolder.first.setText(e.getTit());
        viewHolder.second.setImageResource(e.getIm());

        SVG svg_event = SVGParser.getSVGFromResource(getContext().getResources(), R.raw.eventi_principale);
        viewHolder.second.setImageDrawable(svg_event.createPictureDrawable());
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.HONEYCOMB) {

            viewHolder.second.setLayerType(View.LAYER_TYPE_SOFTWARE, null);

        }
        return convertView;
    }

    public View setSagraItem(ViewHolder viewHolder, EntrySagreEvent e, View convertView){

        viewHolder.first.setText(e.getName());
        viewHolder.first.setTypeface(face, Typeface.BOLD );

        viewHolder.second.setImageResource(R.drawable.shop);

        return convertView;
    }

      private String getHeader(int position) {

          if(getItem(position).getMonth()!=null) {
              return getItem(position).getMonth();
          }
          else
              return null;
      }


    private class ViewHolder {
        public TextView first;
        public ImageView second;
    }
}

我该怎么做才能获得无延迟的卷轴？非常感谢

Answer 1

您想引用 Google 的这篇文章:http://developer.android.com/training/improving-layouts/smooth-scrolling.html

特别是，您应该使用 ViewHolder，这样项目只创建一次，然后重新使用。您会看到性能大大提高。