数据库的初始化和升级（代码）

<?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="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.hanqi.testapp3.TestActivity2"
    android:orientation="vertical">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="初始化数据库"
        android:onClick="bt1_OnClick"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="升级数据库"
        android:onClick="bt2_OnClick"/>


</LinearLayout>

package com.hanqi.testapp3;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class TestActivity2 extends AppCompatActivity {


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test2);

    }

    //初始化数据库
    public void bt1_OnClick(View v)
    {
        //使用工具类得到数据库对象
        MyDBHelper myDBHelper=new MyDBHelper("test.db",2);

        //得到连接
        SQLiteDatabase sd=myDBHelper.getReadableDatabase();

        Toast.makeText(TestActivity2.this, "连接数据库成功", Toast.LENGTH_SHORT).show();

        //关闭连接
        sd.close();
    }

    //升级数据库
    public void bt2_OnClick(View v)
    {
        //使用工具类得到数据库对象
        MyDBHelper myDBHelper=new MyDBHelper("test.db",2);

        //得到连接
        SQLiteDatabase sd=myDBHelper.getWritableDatabase();

        Toast.makeText(TestActivity2.this, "连接数据库成功", Toast.LENGTH_SHORT).show();

        //关闭连接
        sd.close();
    }

   

    //实现SQLiteOpenHelper的内部类
    class MyDBHelper extends SQLiteOpenHelper
    {
        //构造方法
        public MyDBHelper(String dbname,int ver)
        {
            //显示调用父类的构造方法
            //必须在第一行
            super(TestActivity2.this,dbname,null,ver);

        }

        //创建和初始化数据库
        @Override
        public void onCreate(SQLiteDatabase db) {

            //1.执行创建数据库的语句
            String sql="CREATE TABLE t_user" +
                    "(_id  INTEGER PRIMARY KEY " +
                    "AUTOINCREMENT NOT NULL," +
                    "name  VARCHAR(20) NOT NULL," +
                    "sex CHAR(1),age  INTEGER)";
            db.execSQL(sql);

            Log.e("TAG","表创建成功");
            //2.执行初始化数据的语句，insert语句
            ContentValues cv=new ContentValues();

            cv.put("name","张三");
            cv.put("sex","男");
            cv.put("age","20");

            //执行插入,返回主键
            long l=db.insert("t_user",null,cv);

            Log.e("TAG","初始化数据="+l);
        }

        //升级数据库
        //触发条件：当版本号增大
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

            //修改数据
            if(newVersion==2)
            {
                ContentValues cv=new ContentValues();
                cv.put("name","李四");

                String sql="update t_user set name='李四' where  _id=1 ";

                String[] str={"1","18"};
                //调用db的更新方法
                int i=db.update("t_user", cv, "_id=? and age>?",str);

                Log.e("TAG","升级数据 数据条数="+i);
            }

        }
    }
}