AJAX :: How To Use Context Key To Pass Additional Parameters With Cascading DropDownList

I have 3 Dropdownlist 

1-DDlcity   2-DDlRegion    3-DDlDistrict

and below is House_info table

district region city Id can
1 Canada
1 Lon
1 London
2 Ita
2 Canada
3

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)

[Code] ....

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);

[Code] ....

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...