Android-SQLiteOpenHelper

一 概念

是对SOLiteDatabase的封装。主要用于建立和版本号控制，方便我们去建立库表结构

二 用法

又一次封装一个MySqliteOpenHelper类。来实现openOrCreateDatabase类的功能

`public void openOrCreateDatabase()

    {

        try

        {

                MyDatabaseOpenHelper _myDatabaseOpenHelper = new MyDatabaseOpenHelper(mContext, DATABASE_NAME, null, 2);

            mSqLiteDatabase = _myDatabaseOpenHelper.getWritableDatabase();

        } catch (Exception e)

        {

            // TODO: handle exception

            Log.i("chengzhi log", "table exit");

        }

    }

MySqliteOpenHelper类继承SQLiteOpenHelper重写的方法：

onCreate创建表结构

@Override

    public void onCreate(SQLiteDatabase arg0)

    {

        // TODO Auto-generated method stub

        arg0.execSQL("create TABLE "+TABLE_NAME+"(_id INTEGER PRIMARY KEY AUTOINCREMENT,"+COLUMN_USER_NAME+" VARCHAR(50) NOT NULL, "+COLUMN_USER_ADDRESS+" VARCHAR(50) NOT NULL)");

    }

onUpgrade方法用于创建表和控制表的版本号

@Override

    public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2)

    {

        // TODO Auto-generated method stub

        //arg2为新版本号  arg1位旧版本号

        if (2 == arg2)

        {

            arg0.execSQL("create TABLE Custom (_id INTEGER PRIMARY KEY AUTOINCREMENT,"+COLUMN_USER_NAME+" VARCHAR(50) NOT NULL, "+COLUMN_USER_ADDRESS+" VARCHAR(50) NOT NULL)");

        }

        else if (2 == arg1 && 1 == arg2)

        {

            arg0.execSQL("drop TABLE_NAME");

        }

    }