viewlist的数据适配器（以及优化）

学习自慕课网，先扔出一个listview布局(main)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <ListView
        android:id="@+id/lv_main" 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        
        ></ListView>

</LinearLayout>

然后新建一个item.xml，相当于一个实例，随便弄一个实例吧，反正后面用假想数据模拟一下。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >
    
    <ImageView 
        android:id="@+id/iv_image"
        android:layout_width="45dp"
        android:layout_height="60dp"
        android:src="@drawable/four"
        />
    <TextView 
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="30dp"
        android:layout_toEndOf="@+id/iv_image"
        android:text="中津静流"
        android:gravity="center"
        android:textSize="20sp"
        />
    <TextView 
        android:id="@+id/tv_content"
        android:layout_width="match_parent"
        android:layout_height="30dp"
        android:layout_toEndOf="@+id/iv_image"
        android:layout_below="@+id/tv_title"
        android:text="这是我的老婆"
        android:gravity="center_vertical"
        android:textSize="15sp"
        />
</RelativeLayout>

然后在MainActivity中创建假象以及实例化

package com.example.deemo;

import java.util.ArrayList;
import java.util.List;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //创建假想数据
        List<ItemBean> itemBeanList = new ArrayList<ItemBean>();
        for (int i = 0; i < 20; i++) {
            itemBeanList.add(new ItemBean(
                    R.drawable.ic_launcher, 
                    "i am title"+i,
                    "i am content"+i
                    ));
        }
        //实例化
        ListView listView = (ListView) findViewById(R.id.lv_main);
        listView.setAdapter(new MyAdapter(this, itemBeanList));
    }

}

然后创建ItemBean实例化三控件

package com.example.deemo;

public class ItemBean {
    public int ItemImageResid;
    public String Itemtitle;
    public String ItemContent;
    
    public ItemBean(int itemImageResid, String itemtitle, String itemContent) {
        ItemImageResid = itemImageResid;
        Itemtitle = itemtitle;
        ItemContent = itemContent;
    }
        
}

然后在MyAdapter

package com.example.deemo;

import java.util.List;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyAdapter extends BaseAdapter{

    private LayoutInflater mInflater;
    //关联数据源与适配器
    private List<ItemBean> mList; 
    public MyAdapter(Context context,List<ItemBean> list){
        mList = list;
        mInflater = LayoutInflater.from(context);//将xml文件装换成view
    }
    
    @Override
    public int getCount() {//返回ListView数据量
        return mList.size();
    }
    
    //取出所对应的数据项
    @Override
    public Object getItem(int position) {
        return mList.get(position);
    }

    //返回指定索引对应的数据项
    @Override
    public long getItemId(int position) {
        return position;
    }

    //返回每一项内容
    @Override
    public View getView(int positon, View convertView, ViewGroup parent) {
        
        //无缓存机制
/*        View view = mInflater.inflate(R.layout.item, null);//需要装在到item中的文件
        ImageView imageView = (ImageView) view.findViewById(R.id.iv_image);
        TextView title = (TextView) view.findViewById(R.id.tv_title);
        TextView context = (TextView) view.findViewById(R.id.tv_content);
        //取出数据，赋给控件
        ItemBean bean = mList.get(positon);
        imageView.setImageResource(bean.ItemImageResid);
        title.setText(bean.Itemtitle);
        context.setText(bean.ItemContent);
        return view;  
*/
        //普通缓存,避免重复创建
/*        if(convertView == null){//缓存池中是否有
            convertView = mInflater.inflate(R.layout.item, null);
        }
        ImageView imageView = (ImageView) convertView.findViewById(R.id.iv_image);
        TextView title = (TextView) convertView.findViewById(R.id.tv_title);
        TextView context = (TextView) convertView.findViewById(R.id.tv_content);
        //取出数据，赋给控件
        ItemBean bean = mList.get(positon);
        imageView.setImageResource(bean.ItemImageResid);
        title.setText(bean.Itemtitle);
        context.setText(bean.ItemContent);
        return convertView;
*/
        //比较好的优化,避免重复find id
        ViewHolder viewHolder;
        if(convertView == null){
            viewHolder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.item, null);
            //将控件实例化到对象中
            viewHolder.imageView = (ImageView) convertView.findViewById(R.id.iv_image);//关联
            viewHolder.title = (TextView) convertView.findViewById(R.id.tv_title);
            viewHolder.content = (TextView) convertView.findViewById(R.id.tv_content);
            convertView.setTag(viewHolder);//将ViewHolder与conventView绑定
        }else {//通过viewholder对象找到控件
            viewHolder = (ViewHolder) convertView.getTag();
        }
        ItemBean bean = mList.get(positon);
        viewHolder.imageView.setImageResource(bean.ItemImageResid);
        viewHolder.title.setText(bean.Itemtitle);
        viewHolder.content.setText(bean.ItemContent);
        return convertView;
    }
    class ViewHolder{//对应布局控件
        public ImageView imageView;
        public TextView title;
        public TextView content;
    }
}