andriod之自定义适配器与ListView的优化:

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自定义适配器：BaseAdapter

BaseAdapter
   定义: 基本适配器的抽象类，且是ArrayAdapter、SimpleAdapter的父类
   功能：用于实现复杂的数据显示
   需要实现的方法
       public int getCount() 返回数据源的大小
       public long getItemId(int position) 返回指定位置的item控件id
       public Object getItem(int position) 返回指定位置的数据
       public View getView(int position,View convertView,ViewGroup parent) 返回指定位置的控件

ListView的优化:
>1,布局xml文件 listView的高度固定 match_parent 减少getView的次数

>2,判断convertView是否为null 如果为空得话使用布局加载器去创建一个view
       //如果不为空的话直接拿来使用

>3.//将ViewHold保存到convertView中 convertView.setTag(viewHold);
   //将ViewHold从convertView中直接拿出来使用viewHold = (ViewHold) convertView.getTag();

Java代码

import java.util.List;

import android.R.xml;
import android.content.Context;
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.TextView;

import com.qianfeng.day08_baseadaptertest.R;
import com.qianfeng.day08_baseadaptertest.modle.Data;

public class MyAdapter extends BaseAdapter{
   private List<Data> list;
   private Context context;

   public MyAdapter(List<Data> list,Context context){
       this.list = list;
       this.context = context;
   }


   @Override
   public int getCount() {
       // TODO Auto-generated method stub
       return list.size();
   }

   @Override
   public Object getItem(int position) {
       // TODO Auto-generated method stub
       return list.get(position);
   }

   @Override
   public long getItemId(int position) {
       // TODO Auto-generated method stub
       return position;
   }

   @Override
   public View getView(int position, View convertView, ViewGroup parent) {
       // TODO Auto-generated method stub
       Log.i("==getView1==>", "==position==>"+position);
       Log.i("==getView2==>", "==convertView==>"+convertView);

//       View view = LayoutInflater.from(context).inflate(R.layout.item, null);
//       ImageView iv = (ImageView) view.findViewById(R.id.iv);
//       TextView titleViw = (TextView) view.findViewById(R.id.titleView);
//       TextView descView = (TextView) view.findViewById(R.id.descView);
//       TextView dateView = (TextView) view.findViewById(R.id.dateView);
//
//       Data data = list.get(position);
//       iv.setImageResource(data.getImgUrl());
//       titleViw.setText(data.getTitle());
//       descView.setText(data.getDesc());
//       dateView.setText(data.getDate());
//
//       return view;

//       //2
//       //判断convertView是否为null 如果为空得话使用布局加载器去创建一个view
//       //如果不为空的话直接拿来使用
//       if(convertView == null){
//           convertView = LayoutInflater.from(context).inflate(R.layout.item, null);
//       }
//           ImageView iv = (ImageView) convertView.findViewById(R.id.iv);
//           TextView titleViw = (TextView) convertView.findViewById(R.id.titleView);
//           TextView descView = (TextView) convertView.findViewById(R.id.descView);
//           TextView dateView = (TextView) convertView.findViewById(R.id.dateView);
//
//           Data data = list.get(position);
//           iv.setImageResource(data.getImgUrl());
//           titleViw.setText(data.getTitle());
//           descView.setText(data.getDesc());
//           dateView.setText(data.getDate());
//
//       return convertView;

       //第三种
       ViewHold viewHold;
       if(convertView == null){
           convertView = LayoutInflater.from(context).inflate(R.layout.item, null);
           viewHold = new ViewHold();
           viewHold.iv = (ImageView) convertView.findViewById(R.id.iv);
           viewHold.titleViw = (TextView) convertView.findViewById(R.id.titleView);
           viewHold.descView = (TextView) convertView.findViewById(R.id.descView);
           viewHold.dateView = (TextView) convertView.findViewById(R.id.dateView);
           //将ViewHold保存到convertView中
           convertView.setTag(viewHold);
       }
       //将ViewHold从convertView中直接拿出来使用
       viewHold = (ViewHold) convertView.getTag();
           Data data = list.get(position);
           viewHold.iv.setImageResource(data.getImgUrl());
           viewHold.titleViw.setText(data.getTitle());
           viewHold.descView.setText(data.getDesc());
           viewHold.dateView.setText(data.getDate());
       return convertView;
   }


   class ViewHold{
       ImageView iv;
       TextView titleViw;
       TextView descView;
       TextView dateView;
   }

}

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