007_02ListView与BaseAdapter的参数

 BaseAdapter适配器里有个getView()需要重写public View getView(int position,View converView,ViewGroup parent)

　　这个convertView其实就是最关键的部分。原理上讲，当ListView滑动的过程中，会有item被滑出屏幕而不再被使用。这时候Android会回收这个条目的view 这个view也就是这里的convertView当item1被移除屏幕的时候。我们会重新new一个View给新显示的item_new，而如果使用了这个convertView 我们其实可以复用它，这样就省去了new View的大量开销。

package com.example.showdatafromsqlite;

 
public class UserPhone {

     private int id ;
     private String name;
     private String telephone;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getTelephone() {
        return telephone;
    }
    public void setTelephone(String telephone) {
        this.telephone = telephone;
    }
    @Override
    public String toString() {
        return "UserPhone [id=" + id + ", name=" + name + ", telephone="
                + telephone + "]";
    }
    public UserPhone(int id, String name, String telephone) {
        super();
        this.id = id;
        this.name = name;
        this.telephone = telephone;
    }
    public UserPhone() {
        super();
        // TODO Auto-generated constructor stub
    }
 
}

UserPhone.java

package com.example.showdatafromsqlite;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.text.AlteredCharSequence;
import android.util.Log;

public class MydbOpenHelper extends SQLiteOpenHelper {

    //
    public MydbOpenHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
        // TODO Auto-generated constructor stub
    }

    
    //oncreate函数当数据库第一次被创建的时候会调用
    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        String createtable = "create table userphone(id int, name varchar(20), telephone char(11));";
        db.execSQL(createtable);
        
        
        ContentValues c = new ContentValues();
        //id int ,name string ,password string
        for(int i=1;i<50;i++){
            c.put("id", i);
            c.put("name", "user"+i);
            if(i<10)
                c.put("telephone", "1371111111"+i);
            else {
                c.put("telephone", "137111111"+i);
            }
            db.insert("userphone", null, c);
        }
    
        System.out.println("MydbOpenHelper.onCreate()");
    }

    
    //onUpgrade当你的数据库版本升级的时候会调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        //更改数据库的表结构
        //  user(id,name,password)  user(id,name,password,gender)
        //
        //  db.execSQL(""); 
        Log.i("MydbOpenHelper", "oldervserion"+oldVersion+"newversion"+newVersion);
        System.out.println("MydbOpenHelper.onUpgrade()");

    }

}

MydbOpenHelper.java

package com.example.showdatafromsqlite;

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

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
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.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {
    List <UserPhone> list = new ArrayList <UserPhone>();
    UserPhone userPhone;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        MydbOpenHelper helper = new MydbOpenHelper(this, "telphone.db", null, 1);
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor c = db.rawQuery("select * from userphone", null);
        
        while(c.moveToNext()){
            int id = c.getInt(0);
            String name = c.getString(1);
            String telephone = c.getString(2);
            
            Log.i("test", id+","+name+","+telephone);
            userPhone = new UserPhone(id, name, telephone);
            list.add(userPhone);
        }
        db.close();
        
        ListView listView = (ListView)findViewById(R.id.listview);
        BaseAdapter ba = new BaseAdapter(){

            @Override
            public int getCount() {
                // TODO Auto-generated method stub
                return list.size();
            }

            @Override
            public Object getItem(int position) {
                // TODO Auto-generated method stub
                return null;
            }

            @Override
            public long getItemId(int position) {
                // TODO Auto-generated method stub
                return 0;
            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                View v;
                if(convertView == null){
                    v = View.inflate(MainActivity.this, R.layout.itemlayout, null);
                }
                else{
                    v = convertView;
                }
                //往该布局内填充数据
                UserPhone user = list.get(position);
                TextView tv_id = (TextView) v.findViewById(R.id.tv_id);
                TextView tv_name = (TextView) v.findViewById(R.id.tv_name);
                TextView tv_telephone = (TextView) v.findViewById(R.id.tv_telephone);
                
                tv_id.setText(user.getId() + "");
                tv_name.setText(user.getName());
                tv_telephone.setText(user.getTelephone());
                return v;
            }
            
        };
        listView.setAdapter(ba);
        
        
    }


}

MainActivity.java

<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="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.showdatafromsqlite.MainActivity" 
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    <ListView
        android:id="@+id/listview"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:dividerHeight="5dp" >
    </ListView>
   
</LinearLayout>

activity_main.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="vertical" >
    <TextView 
        android:id="@+id/tv_id"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
        />
    <LinearLayout
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:orientation="horizontal">
        <TextView 
        android:id="@+id/tv_name"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
        />
         <TextView 
        android:id="@+id/tv_telephone"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
        />
        
    </LinearLayout>
</LinearLayout>

itemlayout.xml

效果图：（可上下滑动）