基于ViewHolder优化的BaseAdapt

利用优化的BaseAdapter来实现一个ListView效果
1.主activity布局文件如下

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

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

2.新建一个滚动条目的布局文件

<?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="match_parent">

<ImageView
android:layout_width="60dp"
android:layout_height="60dp"
android:id="@+id/iv_image"
android:src="@mipmap/ic_launcher"/>
<TextView
android:layout_width="match_parent"
android:layout_height="30dp"
android:layout_toRightOf="@id/iv_image"
android:text="title"
android:gravity="center"
android:textSize="20sp"
android:id="@+id/tv_titlt"/>
<TextView
android:layout_width="match_parent"
android:layout_height="30dp"
android:layout_below="@id/tv_titlt"
android:text="content"
android:gravity="center_vertical"
android:textSize="16sp"
android:id="@+id/tv_content"
android:layout_toRightOf="@id/iv_image"
/>
</RelativeLayout>

3.新建一个javaBean类用于封装要显示的控件

package com.weixi.baseadapter;

/**
* Created by 风华国乐 on 2016/8/3.
*/
public class ItemBean {
//封装要显示的控件
public int ItemImageResid;
public String ItemTitle;
public String ItemContent;

public ItemBean(int itemImageResid, String itemTitle, String itemContent) {
ItemImageResid = itemImageResid;
ItemTitle = itemTitle;
ItemContent = itemContent;
}
}

4.新建Adapter类继承BaseAdapter(适配器)

package com.weixi.baseadapter;

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 风华国乐 on 2016/8/3.
*/
public class MyAdapter extends BaseAdapter {

private List<ItemBean> mlist;
private LayoutInflater mInflater;

public MyAdapter(Context context,List<ItemBean> list){
mlist=list;
//context是要使用Adapter的界面对象，mInflater是布局装载器对象
mInflater=LayoutInflater.from(context);
}
//返回所需要的数据数量
@Override
public int getCount() {
return mlist.size();
}

//返回所对应的数据项
@Override
public Object getItem(int position) {
return mlist.get(position);
}

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

//返回每一项的显示内容
@Override
public View getView(int position, View convertView, ViewGroup parent) {
//逗逼式，每次都是通过Inflater对象创建一个新的View，并在View中找到相应控件设置相应值，完全没有利用ListView的缓存机制，是对资源的极大浪费

//        View view=mInflater.inflate(R.layout.item,null);
//        ImageView imageView= (ImageView) view.findViewById(R.id.iv_image);
//        TextView title= (TextView) view.findViewById(R.id.tv_titlt);
//        TextView content= (TextView) view.findViewById(R.id.tv_content);
//
//        ItemBean bean=mlist.get(position);
//        imageView.setImageResource(bean.ItemImageResid);
//        title.setText(bean.ItemTitle);
//        content.setText(bean.ItemContent);
//return view;

//普通式，利用了ListView的缓存机制
//        if (convertView==null){
//            //View并未被实例化，缓冲池中无缓存
//            convertView=mInflater.inflate(R.layout.item,null);
//        }
//        ImageView imageView= (ImageView) convertView.findViewById(R.id.iv_image);
//       TextView title= (TextView) convertView.findViewById(R.id.tv_titlt);
//       TextView content= (TextView) convertView.findViewById(R.id.tv_content);
//
//       ItemBean bean=mlist.get(position);
//       imageView.setImageResource(bean.ItemImageResid);
//       title.setText(bean.ItemTitle);
//       content.setText(bean.ItemContent);
//        return convertView;
//文艺式，在文艺式中，我们要避免两个耗时操作，一是重复获取view，二是重复获取findViewById
//不仅 利用了ListView的缓存，更通过ViewHolder类来实现显示数据的视图的缓存，避免多次通过findViewById寻找控件
//首先，创建一个ViewHolder类

class ViewHolder{
public ImageView imageView;
public TextView title;
public TextView content;
}
ViewHolder viewHolder;
if (convertView==null){
viewHolder=new ViewHolder();
viewHolder.imageView=(ImageView) convertView.findViewById(R.id.iv_image);
viewHolder.title=(TextView) convertView.findViewById(R.id.tv_titlt);
viewHolder.content=(TextView) convertView.findViewById(R.id.tv_content);
convertView=mInflater.inflate(R.layout.item,null);
//通过setTag方法将ViewHolder与converview进行关联
convertView.setTag(viewHolder);
}else {
viewHolder= (ViewHolder) convertView.getTag();
}
ItemBean bean=mlist.get(position);
viewHolder.imageView.setImageResource(bean.ItemImageResid);
viewHolder.title.setText(bean.ItemTitle);
viewHolder.content.setText(bean.ItemContent);
return convertView;

}
}

5.在主Activity中添加数据，绑定适配器

package com.weixi.baseadapter;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.ListView;

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

public class MainActivity extends ActionBarActivity {
private ListView listview;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

List<ItemBean> itemBeanList=new ArrayList<>();
for (int i = 0; i <20 ; i++) {
itemBeanList.add(new ItemBean(
R.mipmap.ic_launcher,
"我是标题"+i,
"我是内容"+i
));
}
listview= (ListView) findViewById(R.id.lv_main);
listview.setAdapter(new MyAdapter(this,itemBeanList));
}

}

创建思路



以上内容均出自慕课网eclipse_xu的视频