您能否在此声明之前检查StringDictionary国家/地区是否具有价值.

CountryId = Convert.ToInt32(country.ToString());

为了获得用户选择的值，您必须使用

在下面的语句中使用country ["state"]代替country.ToString().
CountryId = Convert.ToInt32(country.ToString());

Could you please check if the StringDictionary country, has value before this statement.

CountryId = Convert.ToInt32(country.ToString());

Inorder to get the value selected by the user you have to use

country["state"] instead of country.ToString() in the below statement.
CountryId = Convert.ToInt32(country.ToString());

正如你所说，我也尝试过这种方法，但是却得到了同样的错误.我在页面代码后面的代码如下:

as u said,i tried that way also,but getting the same error.my code behind page code is like:

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Web.Services;
public partial class CascadingDropDown : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    [System.Web.Services.WebMethodAttribute(),
    System.Web.Script.Services.ScriptMethodAttribute()]
    public static AjaxControlToolkit.CascadingDropDownNameValue[]
        GetDropDownContents(string knownCategoryValues, string category)
    {
        SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["ajax"].ConnectionString);
        sqlcon.Open();
        DataTable dt = new DataTable();
        SqlDataAdapter da = new SqlDataAdapter("select * from Country", sqlcon);
        da.Fill(dt);
        List values = new List();
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            int CountryId = (int)dt.Rows[i]["countryid"];
            string Countryname = (string)dt.Rows[i]["country"];
            values.Add(new AjaxControlToolkit.CascadingDropDownNameValue(Countryname, CountryId.ToString()));
        }
        return values.ToArray();
    }
    
[System.Web.Services.WebMethodAttribute(),
        System.Web.Script.Services.ScriptMethodAttribute()]
    public static AjaxControlToolkit.CascadingDropDownNameValue[]
        GetDropDownContents2(string knownCategoryValues, string category)
    {
        SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["ajax"].ConnectionString);
        int CountryId;
        StringDictionary categoryvalues = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);
        CountryId = Convert.ToInt32(categoryvalues["state"]);        //CountryId = Convert.ToInt32(categoryvalues["country"]);
        sqlcon.Open();
        DataTable dt1 = new DataTable();
        SqlDataAdapter da1 = new SqlDataAdapter(" select * from State where countryid = @ CountryId", sqlcon);
        da1.Fill(dt1);
        sqlcon.Close();
        List statevalues = new List();
        for (int i = 0; i < dt1.Rows.Count; i++)
        {
            int stateid = (int)dt1.Rows[i]["stateid"];
            string statename = (string)dt1.Rows[i]["state"];
            statevalues.Add(new AjaxControlToolkit.CascadingDropDownNameValue(stateid.ToString(), statename.ToString()));
        }
        return statevalues.ToArray();