ViewHolder优化ListView

viewholder_item.xml  子布局文件

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



    <ImageView
        android:id="@+id/iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

ViewHolderAdapter.java

package sowell.oracle.com.listviewholder;

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;

import java.util.List;

/**
 * Created by 94965 on 2017/11/11.
 */

public class ViewHolderAdapter extends BaseAdapter {

    private List<String> mData;             //储存数据
    private LayoutInflater mInflater;      //实例化布局

    public ViewHolderAdapter(Context context,List<String> data){
        super();
        this.mData=data;
        mInflater=LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return mData.size();
    }

    @Override
    public Object getItem(int position) {
        return mData.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder=null;
        //判断是否缓存
        if(convertView==null){
            holder=new ViewHolder();
            //通过LayoutInflater实例化布局
            convertView=mInflater.inflate(R.layout.viewholder_item,null);
            holder.img=(ImageView)convertView.findViewById(R.id.iv);
            holder.title=(TextView)convertView.findViewById(R.id.tv);
            convertView.setTag(holder);
        }else {
            //通过tag找到缓存‘的布局
            holder=(ViewHolder)convertView.getTag();
        }

        //设置布局中控件要显示的视图
        holder.img.setBackgroundResource(R.mipmap.ic_launcher);
        holder.title.setText(mData.get(position));
        return convertView;
    }



    public final class ViewHolder{
        public ImageView img;
        public TextView title;
    }
}

activity.xml 总布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    tools:context="sowell.oracle.com.listviewholder.MainActivity">

    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"></ListView>


</LinearLayout>

MainActivity.java

package sowell.oracle.com.listviewholder;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {

    public ListView listView;
    public ViewHolderAdapter adapter;
    public List<String> list;
    public String string;


    public void init(){

        list=new ArrayList<String>();
        for(int i=0;i<=20;i++)
        {
            string=""+i;
            list.add(string);
        }
        adapter=new ViewHolderAdapter(this,list);
        listView=(ListView)findViewById(R.id.lv);
        listView.setAdapter(adapter);
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }
}