How to use context key to pass additional parameters with AJAX Cascading DropDownList in ASP.Net

Hi

I have 3 Dropdownlist 

1-DDlcity   2-DDlRegion    3-DDlDistrict

and below is House_info table

now when I select city from DDlcity after that select region from DDlregion according to my selected item from DDlcity and DDlregion it bind DDlDistrict...

before I used OnselectedIndexChange below is SP...

ALTER procedure [dbo].[SelectِDistrict] 
@Region NVARCHAR(30),
@city NVARCHAR(40)
AS
BEGIN
	SELECT ID,Centername
	FROM District
	WHERE (Region=@Region or @Region='0') and (city=@city or @city='0')
	ORDER BY Centername ASC
END

it worked correctly

but now I use cascadingdropdown list 

 [WebMethod]
    public CascadingDropDownNameValue[] GetDistrict(string knownCategoryValues)
    {
        string region = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["Region"];
        string query = string.Format("SELECT District FROM District WHERE Region = N'{0}'", region);
        List<CascadingDropDownNameValue> district = GetData(query);
        return district.ToArray();
    }

problem is that when I select city=canada  then region=1 I want it bind in DDldistrict =can  but here it show in DDLdistrict can and Lon

here it just select district that region=1 it doesn't attention to city selected Item I want it do  like SP that I used...

Best Regrads

Neda