android之listView缓存机制

activity_main.xml：

<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:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.day_05_06.MainActivity" >

<ListView

android:id="@+id/lvGenerals"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:divider="#ccc"

android:dividerHeight="20dp"/>

</RelativeLayout>

MainActivity.java：

package com.example.day_05_06;

import java.util.ArrayList;

import java.util.List;

import com.litsoft.General.General;

import android.support.v7.app.ActionBarActivity;

import android.content.Context;

import android.os.Bundle;

import android.util.Log;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Adapter;

import android.widget.BaseAdapter;

import android.widget.ImageView;

import android.widget.ListView;

import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

private ListView lvGenerals;//listView对象

private List<General> generals ;//数据集合

private BaseAdapter adapter;//适配器

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

initData();

initView();

}

private void initView() {

// TODO Auto-generated method stub

lvGenerals = (ListView) findViewById(R.id.lvGenerals);

adapter = new GeneralAdapter(this,generals);

lvGenerals.setAdapter(adapter);

}

private void initData() {

// TODO Auto-generated method stub

generals = new ArrayList();

int [] images = new int[] {

R.drawable.baiqi,R.drawable.caocao,R.drawable.chengjisihan,

R.drawable.hanxin,R.drawable.lishimin,R.drawable.nuerhachi,

R.drawable.sunbin,R.drawable.sunwu,R.drawable.yuefei,

R.drawable.zhuyuanzhang

};

String [] names = getResources().getStringArray(R.array.generals);

for(int i=0;i<images.length;i++){

General general = new General(images[i],names[i]);

generals.add(general);

}

}

class GeneralAdapter extends BaseAdapter{

private Context context;

private List<General> innerGenerals;

public GeneralAdapter(Context context, List<General> innerGenerals) {//这里用构造器的方式传递外部类的上下文对象和General集合对象

super();

this.context = context;

this.innerGenerals = innerGenerals;

}

@Override

public int getCount() {

// TODO Auto-generated method stub

return generals.size();

}

@Override

public General getItem(int position) {

// TODO Auto-generated method stub

return generals.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("main", position+"");

ViewHolder viewHolder = null;

if(convertView == null){//第一屏中尚未创建列表项时

viewHolder = new ViewHolder ();

convertView = View.inflate(context, R.layout.general, null);

viewHolder.ivGerneral = (ImageView) convertView.findViewById(R.id.ivThumb);

viewHolder.tvName = (TextView)convertView.findViewById(R.id.tvName);

convertView.setTag(viewHolder);//这里相当于初始化一次用于适配的布局，以后都用这个布局了，就是滚动的时候就不用再初始化用于适配的布局

}else{//以后的滚动，出现其他的列表项

viewHolder = (ViewHolder) convertView.getTag();

}

General general = this.innerGenerals.get(position);

viewHolder.ivGerneral.setImageResource(general.getImageSrc());

viewHolder.tvName.setText(general.getName());

return convertView;

}

}

class ViewHolder{//用于适配布局的具体项

ImageView ivGerneral;

TextView tvName;

}

}

适配的页面布局：general.xml

<?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="horizontal" >

<ImageView

android:id="@+id/ivThumb"

android:layout_width="60dp"

android:layout_height="60dp"

android:src="@drawable/baiqi"/>

<TextView

android:id="@+id/tvName"

android:layout_width="match_parent"

android:layout_height="60dp"

android:text="白起"

/>

</LinearLayout>

General.java：

package com.litsoft.General;

public class General {

private int imageSrc;

private String name;

public int getImageSrc() {

return imageSrc;

}

public void setImageSrc(int imageSrc) {

this.imageSrc = imageSrc;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public General(int imageSrc, String name) {

super();

this.imageSrc = imageSrc;

this.name = name;

}

}

strings.xml：

<?xml version="1.0" encoding="utf-8"?>

<resources>

<string name="app_name">Day_05_06</string>

<string name="hello_world">Hello world!</string>

<string name="action_settings">Settings</string>

<string-array name="generals">

<item>白起</item>

<item>曹操</item>

<item>成吉思汗</item>

<item>韩信</item>

<item>李世民</item>

<item>努尔哈赤</item>

<item>孙膑</item>

<item>孙武</item>

<item>朱元璋</item>

<item>岳飞</item>

</string-array>

</resources>

效果：