我做了个条件查询，但是只能查询一次？不知道怎么办，请高手看看哪错了！

Question

        //这是界面层
        /// <summary>
        /// 按费用要求搜索客房记录
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_roomPrerequisite_Click(object sender, EventArgs e)
        {
            string price = tbx_price.Text;
            try
            {
                if (tbx_price.Text.Trim() == "") MessageBox.Show("请输入费用范围", "提示您");
                if (dGV_rCheckPrice.DataSource != null)
                {
                    dGV_rCheckPrice.DataSource = null;
                    dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
                    tbx_price.Text = null;
                }
                else
                {
                    dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
                    tbx_price.Text = null;
                }
            }
            catch 
            {
                return;
            }
        }
         //这是业务逻辑层
         /// <summary>
        /// 按“费用范围”查询
        /// </summary>
        /// <param name="price"></param>
        /// <returns></returns>
        internal object checkPrice(string price)
        {
            return mydb.checkPrice(price);
        }
        //这是数据访问层
        /// <summary>
        /// 按“费用范围”返回数据记录
        /// </summary>
        /// <param name="price"></param>
        /// <returns></returns>
        internal object checkPrice(string price)
        {
            cmd.CommandText = "select * from roomInfo where rent<=@price";
            cmd.Parameters.AddWithValue("@rent", price);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }

Answer 1

第二次查询表格空了？
cmd怎么定义的？

Answer 2

internal object checkPrice(string price)
{
   cmd=new SqlCommand();//这里加个看看
   cmd.CommandText = "select * from roomInfo where rent<=@price";
   cmd.Parameters.AddWithValue("@rent", price);
   OleDbDataAdapter da = new OleDbDataAdapter();
   da.SelectCommand = cmd;
   DataTable dt = new DataTable();
   da.Fill(dt);
   return dt;
}

Answer 3

你把数据源给清了，到第二次绑定的时候要再使用一下databind（）

Answer 4

tbx_price.Text = null;
你想干嘛?
点击按钮后清空文本框? 那这样写tbx_price.Text = "";
不然你的这句话就会影响你下次查询的那个price.

Answer 5

你把数据源给清了，到第二次绑定的时候要再使用一下databind（）----要重新邦定

Answer 6

 try
            {
                if (tbx_price.Text.Trim() == "") MessageBox.Show("请输入费用范围", "提示您");
                if (dGV_rCheckPrice.DataSource != null)
                {
                    dGV_rCheckPrice.DataSource = null;
                    dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
                    tbx_price.Text = null;
                }
                else这段代码,我觉得就不用要吧~~~~

Answer 7

 两处 dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
下都加上dGV_rCheckPrice.DataBind();

Answer 8

很郁闷还有查一次,二次失效的,这么奇怪!
if (tbx_price.Text.Trim() == "") MessageBox.Show("请输入费用范围", "提示您");建议这行这样写if (tbx_price.Text.Trim() == "") {
MessageBox.Show("请输入费用范围", "提示您");
return;
}

Answer 9

        public DbAccess(string path)
        {
            string connStr = "";
            conn = new OleDbConnection();//初始化conn
            connStr = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + path;
            conn.ConnectionString = connStr;
            cmd = new OleDbCommand();
            cmd.Connection = conn;
        }

Answer 10

还有一个问题，我做上面的查询后再做下面的查询时 ，下面的结果始终我空。反之亦然。真实奇怪！！！
现在把代码都贴出来了，请高手帮忙看看！！！
这是界面层        private void btn_all_Click(object sender, EventArgs e)
        {
            bool toilet = true;
            bool adsl = true;
            bool tel = true;
            if (dGV_roomCheck.DataSource != null)
            {
                dGV_roomCheck.DataSource = null;
                dGV_roomCheck.DataSource = mybo.checkAllGInfo(toilet, adsl, tel);
            }
            else
            {
                dGV_roomCheck.DataSource = mybo.checkAllGInfo(toilet, adsl, tel);
            }
        }
          private void rB_tel_CheckedChanged(object sender, EventArgs e)
        {
            bool tel = true;
            if (dGV_roomCheck.DataSource != null)
            {
                dGV_roomCheck.DataSource = null;
                dGV_roomCheck.DataSource = mybo.checkTel(tel);
            }
            else
            {
                dGV_roomCheck.DataSource = mybo.checkTel(tel);
            }
        }
         private void rB_toilet_CheckedChanged(object sender, EventArgs e)
        {
            bool toilet = true;
            if (dGV_roomCheck.DataSource != null)
            {
                dGV_roomCheck.DataSource = null;
                dGV_roomCheck.DataSource = mybo.checkToil(toilet);
            }
            else
            {
                dGV_roomCheck.DataSource = mybo.checkToil(toilet);
            }
        }
        private void rB_adsl_CheckedChanged(object sender, EventArgs e)
        {
            bool adsl = true;
            if (dGV_roomCheck.DataSource != null)
            {
                dGV_roomCheck.DataSource = null;
                dGV_roomCheck.DataSource = mybo.checkAdsl(adsl);
            }
            else
            {
                dGV_roomCheck.DataSource = mybo.checkAdsl(adsl);
            }
        }        private void btn_roomPrerequisite_Click(object sender, EventArgs e)
        {
            string price = tbx_price.Text;
            try
            {
                if (tbx_price.Text.Trim() == "")
                {
                    MessageBox.Show("请输入费用范围", "提示您");
                    return;
                }
                if (dGV_rCheckPrice.DataSource != null)
                {
                    dGV_rCheckPrice.DataSource = null;
                    dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
                    tbx_price.Text = "";
                }
                else
                {
                    dGV_rCheckPrice.DataSource = mybo.checkPrice(price);
                    tbx_price.Text = "";
                }
            }
            catch
            {
                return;
            }
        }
        private void tbx_price_TextChanged(object sender, EventArgs e)
        {
            try
            {
                if (double.Parse(tbx_price.Text) < 200 && double.Parse(tbx_price.Text) > 0)
                {                }
                else if (double.Parse(tbx_price.Text) > 200)
                {
                    MessageBox.Show("输入值太大了", "提示您");
                    tbx_price.Text = "";
                    return;
                }
            }
            catch
            {
                tbx_price.Text = "";
                return;
            }        }

Answer 11

这里是 业务逻辑层class BusinessLogic
    {
        DbAccess mydb = new DbAccess(@" + Application.StartupPath + myDbAccess.mdb");//实例化数据访问层        internal object checkAdsl(bool adsl)
        {
            return mydb.checkAdsl(adsl);
        }        internal object checkToil(bool toilet)
        {
            return mydb.checkToil(toilet);
        }
 
        internal object checkTel(bool tel)
        {
            return mydb.checkTel(tel);
        }
        internal object checkAllGInfo(bool toilet, bool adsl, bool tel)
        {
            return mydb.checkAllGInfo(toilet,adsl,tel);
        }
        internal object checkPrice(string price)
        {
            return mydb.checkPrice(price);
        }
    } 

Answer 12

这是数据访问层class DbAccess
    {   
        public DbAccess(string path)
        {
            string connStr = "";
            conn = new OleDbConnection();//初始化conn
            connStr = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + path;
            conn.ConnectionString = connStr;
            cmd = new OleDbCommand();
            cmd.Connection = conn;
        }
        private OleDbConnection conn;//定义连接对象
        private OleDbCommand cmd;  //定义命令对象
     
        private bool OpenConn()//打开数据库数据连接
        {
            if (conn.State != ConnectionState.Open)//判断数据库连接是否打开
            {
                conn.Open();
                return true;
            }
            else
            {
                return false;
            }
        }
               private bool CloseConn()//关闭数据库连接
        {
            if (conn.State != ConnectionState.Closed)//判断数据库连接是否关闭
            {
                conn.Close();
                return true;
            }
            else
            {
                return false;
            }
        }
      internal object getAllData(string p)//从逻辑层传入表名,访问数据层
        {
            cmd.CommandText = "select * from " + p;
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;           
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
        internal object checkAdsl(bool adsl)
        {
            cmd.CommandText = "select * from roomInfo where haveADSL=@adsl";
            //cmd.Parameters.AddWithValue("@toilet", toilet);
            //cmd.Parameters.AddWithValue("@tel", tel);
            cmd.Parameters.AddWithValue("@adsl", adsl);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
   
        internal object checkToil(bool toilet)
        {
            cmd.CommandText = "select * from roomInfo where haveToilet=@toilet";
            cmd.Parameters.AddWithValue("@toilet", toilet);
            //cmd.Parameters.AddWithValue("@tel", tel);
            //cmd.Parameters.AddWithValue("@adsl", adsl);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
     
        internal object checkTel(bool tel)
        {
            cmd.CommandText = "select * from roomInfo where haveTel=@tel";
            cmd.Parameters.AddWithValue("@tel", tel);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
        internal object checkAllGInfo(bool toilet, bool adsl, bool tel)
        {
            cmd.CommandText = "select * from roomInfo where haveADSL=@adsl and haveToilet =@toilet and havetel=@tel";
            cmd.Parameters.AddWithValue("@toilet", toilet);
            cmd.Parameters.AddWithValue("@tel", tel);
            cmd.Parameters.AddWithValue("@adsl", adsl);
            OleDbDataAdapter da = new OleDbDataAdapter();
            da.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }
         internal object checkPrice(string price)
        {
            cmd.CommandText = "select * from roomInfo where rent<=@price";
            cmd.Parameters.AddWithValue("@rent", price);
            OleDbDataAdapter da1 = new OleDbDataAdapter();
            da1.SelectCommand = cmd;
            DataTable dt = new DataTable();
            da1.Fill(dt);
            return dt;
        }
    }