Android控件之ListView探究二

目录结构

main.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<!-- 使用相对布局 -->
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <TextView android:layout_width="100dip"
        android:layout_height="wrap_content"
        android:layout_marginLeft="30dip"
        android:textSize="20dip"
        android:id="@+id/id"/>
    <TextView android:layout_width="100dip"
        android:layout_height="wrap_content"
        android:layout_alignTop="@id/id"
        android:layout_toRightOf="@id/id"
        android:textSize="20dip"
        android:id="@+id/name"/>
    <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@id/name"
        android:layout_toRightOf="@id/name"
        android:textSize="20dip"
        android:id="@+id/age"/>
</RelativeLayout>

实体JavaBean

package com.ljq.domain;


public class Person {

    private String id;
    private String name;
    private String age;

    public Person() {
        super();
    }

    public Person(String id, String name, String age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }
}

自定义适配器PersonAdapter

package com.ljq.ls;

import java.util.List;

import com.ljq.domain.Person;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
/**
 * ListView加载adapter的过程
 * 
 * 1、先判断adapter有多少数据项，根据这个数据确定有多少个item
 * 
 * 2、确定每个item里加载哪个view
 * 
 * 3、在view里加载要显示的数据
 * 
 * @author jiqinlin
 *
 */
public class PersonAdapter extends ArrayAdapter{
    private LayoutInflater layoutInflater = null;
    private List<Person> persons;

    public PersonAdapter(Context context, int textViewResourceId, List objects) {
        super(context, textViewResourceId, objects);
        layoutInflater = LayoutInflater.from(context);
        persons = objects;
    }
    
    /**
     * 获取adapter里有多少个数据项
     */
    @Override
    public int getCount() {
        return persons.size();
    }

    @Override
    public Object getItem(int position) {
        return persons.get(position);
    }
    
    @Override
    public long getItemId(int position) {
        return position;
    } 
    
    /**
     * 创建显示的数据界面
     * 
     * Adapter的作用就是ListView界面与数据之间的桥梁，
     * 当列表里的每一项显示到页面时，都会调用Adapter的getView方法返回一个View。
     * 想过没有？ 在我们的列表有1000000项时会是什么样的？是不是会占用极大的系统资源？
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        /*
        // 优化前
        ViewHolder holder = new ViewHolder();
        convertView = layoutInflater.inflate(R.layout.main, null);
        holder.id = (TextView)convertView.findViewById(R.id.id);
        holder.name = (TextView)convertView.findViewById(R.id.name);
        holder.age = (TextView)convertView.findViewById(R.id.age);
        convertView.setTag(holder);
        
        holder.id.setText(persons.get(position).getId());
        holder.name.setText(persons.get(position).getName());
        holder.age.setText(persons.get(position).getAge());
        return convertView;
        */
        
        // 优化后
        ViewHolder holder;
        if(convertView == null){
            convertView = layoutInflater.inflate(R.layout.main, null);
            holder = new ViewHolder();
            holder.id = (TextView)convertView.findViewById(R.id.id);
            holder.name = (TextView)convertView.findViewById(R.id.name);
            holder.age = (TextView)convertView.findViewById(R.id.age);
            convertView.setTag(holder);
        }else{
            holder = (ViewHolder)convertView.getTag();
        }
        
        holder.id.setText(persons.get(position).getId());
        holder.name.setText(persons.get(position).getName());
        holder.age.setText(persons.get(position).getAge());
        return convertView;
    }
    
    /**
     * 界面上的显示控件
     * 
     * @author jiqinlin
     *
     */
    private static class ViewHolder{
        private TextView id;
        private TextView name;
        private TextView age;
    }
    

}

类LsActivity

package com.ljq.ls;

import java.util.ArrayList;

import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ListView;
import android.widget.Toast;

import com.ljq.domain.Person;

public class LsActivity extends ListActivity {
    private ArrayList<Person> persons = new ArrayList<Person>();
    private PersonAdapter personAdapter = null;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        initData();
        personAdapter =new PersonAdapter(LsActivity.this, R.layout.main, persons);
        setListAdapter(personAdapter);
        registerForContextMenu(getListView());
    }
    
    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        Person person = persons.get(position);
        Toast.makeText(LsActivity.this, person.getId()+":"+person.getName()
                +":"+person.getAge(), Toast.LENGTH_LONG).show();
        return;
    }

    private void initData(){
        persons.add(new Person("序号", "姓名", "年龄"));
        persons.add(new Person("1", "ljq1", "20"));
        persons.add(new Person("2", "ljq2", "20"));
        persons.add(new Person("3", "ljq3", "20"));
        persons.add(new Person("4", "ljq4", "20"));
        persons.add(new Person("5", "ljq5", "20"));
        persons.add(new Person("6", "ljq6", "20"));
        persons.add(new Person("7", "ljq7", "20"));
        persons.add(new Person("8", "ljq8", "20"));
        persons.add(new Person("9", "ljq9", "20"));
    }
}

运行结果