最近项目不是很忙，刚好在看代码的时候，看到了数据库这一块，感觉好长时间没用，也都忘记了，也就顺便复习一下。

由于android中google给我们提供了sqliteOpenHelper这个类来帮助我们操作数据库，所以我们第一步自然是要继承这个类：

public class DBHtlper extends sqliteOpenHelper {

    public DBHtlper(Context context,String name,sqliteDatabase.CursorFactory factory,int version) {
        super(context,name,factory,version);
    }

    @Override
    public void onCreate(sqliteDatabase sqliteDatabase) {
        //创建一个表，id 主键，自动增长 username、password 字符类型
        String sql = "create table user(id integer primary key autoincrement,username varchar(20) not null,password varchar(20) not null);";
        sqliteDatabase.execsql(sql);
    }

    @Override
    public void onUpgrade(sqliteDatabase sqliteDatabase,int i,int i1) {
        sqliteDatabase.execsql("DROP TABLE IF EXISTS user");
        onCreate(sqliteDatabase);
    }
}

然后创建一个sql帮助类，分别执行增、删、改、查的操作：

<span style="font-family:SimSun;font-size:14px;">    public sqliteUtils(Context context) {
        //创建数据库Person.db
        dbHtlper = new DBHtlper(context,"Person.db",null,1);
    }

    /**
     * 插入数据
     *
     * @param user
     */
    public void insertData(User user) {
        String sql = "insert into user(username,password) values(?,?)";
        //获得数据库的操作
        sqliteDatabase database = dbHtlper.getWritableDatabase();
        database.execsql(sql,new Object[]{user.getUsername(),user.getPassword()});
        database.close();
    }

    /**
     * 更新数据
     *
     * @param user
     */
    public void updateData(User user) {
        String sql = "update user set username = ?,password = ? where id = ?";
        sqliteDatabase database = dbHtlper.getWritableDatabase();
        database.execsql(sql,user.getPassword(),user.getId()});
        database.close();
    }

    /**
     * 删除数据
     *
     * @param user
     */
    public void deleteData(User user) {
        String sql = "delete from user where id = ? or username = ?";
        sqliteDatabase database = dbHtlper.getWritableDatabase();
        database.execsql(sql,new Object[]{user.getId(),user.getUsername()});
        database.close();
    }

    /**
     * 查询
     */
    public User selectData(String userName) {
        User user = null;
        String sql = "select * from user where username like ?";
        sqliteDatabase database = dbHtlper.getReadableDatabase();
        Cursor cursor = database.rawQuery(sql,new String[]{"%"+userName+"%"});
        while (cursor.moveToNext()) {//只取第一条
            user = new User();
            user.setId(cursor.getInt(cursor.getColumnIndex("id")));
            user.setUsername(cursor.getString(cursor.getColumnIndex("username")));
            user.setPassword(cursor.getColumnName(cursor.getColumnIndex("password")));
            database.close();
            return user;
        }
        return user;
    }</span>