第二阶段冲刺4

1、我昨天的成就：成功连接上数据库
2、遇到什么困难：一些语句的操作看不懂，里面有很多不懂得参数
3、今天的任务：实现能查看数据库，让数据可视化。

package com.example.lenovo.share;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;


public class DbHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "share.db";
    private static final String TBL_NAME = "user";
    private static final String CREATE_TBL = "create table user " +
            "(username varchar(20) primary key ,password varchar(20))";
    private SQLiteDatabase db;

    public DbHelper(Context context) {
        super(context, DB_NAME, null, 1);
    }

    public DbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory,
                    int version) {
        super(context, name, factory, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //创建数据库及表格
        db.execSQL(CREATE_TBL);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public void open() {
        db = getWritableDatabase();
    }

    public void close() {
        if (db != null) {
            db.close();
        }
    }
}