android下创建数据库学习笔记

##在Android中创建一个数据库##

###步骤###

1、创建一个类继承SQLiteOpenHelper并在类中重写父类的构造方法、onCreate方法、onGrade方法（数据库的版本只能升级，不能降级）

###数据库增删改查方法##
    public void add(View view){
        SQLiteDatabase db = sql.getWritableDatabase();
        //Random random = new Random();    
        //在数据库中增加一条数据
        db.execSQL("insert into info (name,phone) values (?,?)", new Object[]{"张三","123456"});
        db.execSQL("insert into info (name,phone) values (?,?)", new Object[]{"李四","654321"});
        Toast.makeText(this,"add successfully!",Toast.LENGTH_SHORT).show();
        db.close();
    }
    public void delete(View view){
        SQLiteDatabase db = sql.getWritableDatabase();
        //在数据库中删除指定数据
        db.execSQL("delete from info where name=?", new Object[]{"张三"});
        Toast.makeText(this,"delete successfully!",Toast.LENGTH_SHORT).show();
        db.close();
    }
    public void upgrade(View view){
        SQLiteDatabase db = sql.getWritableDatabase();
        //在数据库中修改指定数据
        db.execSQL("update info set phone=? where name=?", new Object[]{"111111","李四"});
        Toast.makeText(this,"upgrade successfully!",Toast.LENGTH_SHORT).show();
        db.close();
    }
    public void checkAll(View view){
        SQLiteDatabase db = sql.getReadableDatabase();
        //查询数据库并返回游标集cursor
        Cursor cursor = db.rawQuery("select * from info", null);
        //创建List集合
        List<Person>list = new ArrayList<Person>();
        //通过while循环遍历数据库数据
        while(cursor.moveToNext()){
            Person person = new Person();
            person.setId(cursor.getInt(cursor.getColumnIndex("_id")));
            person.setName(cursor.getString(cursor.getColumnIndex("name")));
            person.setPhone(cursor.getString(cursor.getColumnIndex("phone")));
            list.add(person);
            person=null;
        }
        cursor.close();
        //遍历List集合
        for(Person p:list){
            System.out.println(p.toString());
        }
        Toast.makeText(this,"checkAll successfully!",Toast.LENGTH_SHORT).show();
        db.close();
    }