清除回发时的查询字符串

简单的问题，但我不知道该怎么做。我有一个带有 GridView 的页面，最初使用查询字符串填充。

获取查询字符串值后，我不需要查询字符串，因为我使用 DropDownList 的值来填充 GridView。

我怎样才能摆脱它？

回发并不能清除它，它只是继续标记。

我尝试了 Request.QueryString.Clear，但出现“只读”错误。

我将非常感谢您在解决这个问题时为我提供的任何帮助。

EDIT 1

using System;
using System.Configuration;
using System.Data;
using System.Data.Odbc;
using System.Globalization;
using System.Threading;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Reflection;

public partial class GV : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            my_DDL();
            GridViewBind();
        }
    }

    protected void my_DDL()
    {
      ....... 
    }

    protected void DDL_SelectedIndexChanged(object sender, EventArgs e)
    {
        PropertyInfo Isreadonly = typeof(System.Collections.Specialized.NameValueCollection).GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic);
        Isreadonly.SetValue(Request.QueryString, false, null);
        Request.QueryString.Clear(); 
    }

    public DataTable GridViewBind()
    {
      //here use in the query the value of querystring or DDL value

    }

}

EDIT 2

using System;
using System.Configuration;
using System.Data;
using System.Data.Odbc;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class GV : System.Web.UI.Page
{
    OdbcConnection myConnectionString =
       new OdbcConnection(ConfigurationManager.ConnectionStrings["ConnMySQL"].ConnectionString);

    OdbcDataAdapter dadapter;
    DataSet dset;
    DataTable dt = new DataTable();
    string sql1;
    string sql2;

    protected void Page_Load(object sender, EventArgs e)
    {       
        if (!IsPostBack)
        {
            RTD_DDL();

            if (Request.QueryString["RTD"].ToString() != "")
            {
                RTD.SelectedValue = Request.QueryString["RTD"].ToString();
            }

            if (Request.QueryString["Month"].ToString() != "")
            {
                MonthYear.SelectedValue = Request.QueryString["Month"].ToString();
            }

            GridViewBind();
        }
    }

    protected void MonthYear_SelectedIndexChanged(object sender, EventArgs e)
    {
        GridViewBind();
    }

    protected void RTD_DDL()
    {
        RTD.AppendDataBoundItems = true;

        string strQuery = " SELECT ... ; ";

        OdbcCommand objCmd = new OdbcCommand(strQuery, myConnectionString);
        objCmd.CommandType = CommandType.Text;
        objCmd.CommandText = strQuery;

        try
        {
            myConnectionString.Open();
            RTD.DataSource = objCmd.ExecuteReader();
            RTD.DataTextField = "RTD1";
            RTD.DataValueField = "RTD";
            RTD.DataBind();
            RTD.Items.Add(new ListItem("------", ""));
            RTD.Items.Add(new ListItem("1", "1"));
            RTD.AppendDataBoundItems = true;
            GridViewBind();
        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            myConnectionString.Close();
        }
    }

    protected void RTD_SelectedIndexChanged(object sender, EventArgs e)
    {
        MonthYear.Items.Clear();
        MonthYear.Items.Add(new ListItem("------", ""));
        MonthYear.AppendDataBoundItems = true;

        if (RTD.SelectedItem.Value == "1")
        {
            sql1 = " SELECT ... ; ";
        }
        else
        {
            sql1 = " SELECT ...; ";
        }


        OdbcCommand objCmd = new OdbcCommand(sql1, myConnectionString);
        objCmd.Parameters.AddWithValue("?", RTD.SelectedItem.Value);

        objCmd.CommandType = CommandType.Text;
        objCmd.CommandText = sql1;
        objCmd.Connection = myConnectionString;

        try
        {
            myConnectionString.Open();
            MonthYear.DataSource = objCmd.ExecuteReader();
            MonthYear.DataTextField = "value1";
            MonthYear.DataValueField = "value2";
            MonthYear.DataBind();
            GridViewBind();

            if (MonthYear.Items.Count > 1)
            {
                MonthYear.Enabled = true;
            }
            else
            {
                MonthYear.Enabled = false;
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            myConnectionString.Close();
        }
    }

    public DataTable GridViewBind()
    {

        sql2 = " SELECT ... ; ";

        try
        {
            dadapter = new OdbcDataAdapter(sql2, myConnectionString);

            if (Request.QueryString["RTD"] != "")
            {
                dadapter.SelectCommand.Parameters.Add("param1", Request.QueryString["RTD"].ToString());
            }

            if (RTD.SelectedIndex != 0)
            {
                dadapter.SelectCommand.Parameters.Add("param1", RTD.SelectedValue.ToString());
            }

            dadapter.SelectCommand.Parameters.Add("param2", MonthYear.SelectedValue.ToString());
            dset = new DataSet();
            dset.Clear();
            dadapter.Fill(dset);
            DataTable dt = dset.Tables[0];
            GridView1.DataSource = dt;
            GridView1.DataBind();
            return dt;
        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            dadapter.Dispose();
            dadapter = null;
            myConnectionString.Close();
        }
    }
}

This may成为您正在寻找的东西（它使用 System.Reflection）

PropertyInfo Isreadonly = typeof(System.Collections.Specialized.NameValueCollection).GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic);

Isreadonly.SetValue(Request.QueryString, false, null);

Request.QueryString.Clear();