Three-Level linkage drop-down menu

Write CS,
AJAX can also be using system;
Using system. Data;
Using system. configuration;
Using system. Web;
Using system. Web. Security;
Using system. Web. UI;
Using system. Web. UI. webcontrols;
Using system. Web. UI. webcontrols. webparts;
Using system. Web. UI. htmlcontrols;
Using system. Data. sqlclient;
/// <Summary>
/// Summary of provcityservstat
/// This class is mainly used when the province/city/service station are all pulled into the judgment, the province and city teachers are both autopostback
/// </Summary>
Public class provcityservstat
{
Public dropdownlist prov;
Public dropdownlist city;
Public dropdownlist servstat;
Public String servstat_id;
Public provcityservstat ()
{
//
// Todo: add the constructor logic here
//
}
// Drop-down list of province bound
Public void databindtoprov ()
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_prov", con );
Sqldatareader SDR = cmd. executereader ();
This. Prov. datasource = SDR;
This. Prov. datatextfield = "prov_name ";
This. Prov. datavaluefield = "prov_id ";
This. Prov. databind ();
SDR. Close ();
Con. Close ();
}

// Bind the city drop-down list
Public void databindtocity ()
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_city where city_provid =" + this. Prov. selectedvalue, con );
Sqldatareader SDR = cmd. executereader ();
This. City. datasource = SDR;
This. City. datatextfield = "city_name ";
This. City. datavaluefield = "city_id ";
This. City. databind ();
SDR. Close ();
Con. Close ();
}

// Bind the service station
Public void databindtoservstat ()
{
If (this. City. selectedvalue! = "")
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_servstat where servstat_cityid =" + this. City. selectedvalue, con );
Sqldatareader SDR = cmd. executereader ();
This. servstat. datasource = SDR;
This. servstat. datatextfield = "servstat_name ";
This. servstat. datavaluefield = "servstat_id ";
This. servstat. databind ();
SDR. Close ();
Con. Close ();
}
Else
{
This. servstat. Items. Clear ();
}
}

// It is generally used for the drop-down of provinces, cities, and service stations when new users are added.
Public void databindadd ()
{
Databindtoprov ();
Databindtocity ();
Databindtoservstat ();
}

// When the province drop-down changes
Public void databinddropdownprov ()
{
Databindtocity ();
Databindtoservstat ();
}

// The following is used for modification. Based on the known servstat_id, determine the service station, city, and province.
Public void databindmod ()
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_servstat, t_city, t_prov where prov_id = city_provid and city_id = servstat_cityid and servstat_id =" + servstat_id, con );
Sqldatareader SDR = cmd. executereader ();
If (SDR. Read ())
{
Databindmodprov (SDR ["prov_id"]. tostring ());
Databindmodcity (SDR ["prov_id"]. tostring (), SDR ["city_id"]. tostring ());
Databindmodservstat (SDR ["city_id"]. tostring (), SDR ["servstat_id"]. tostring ());
}
SDR. Close ();
Con. Close ();
}

// Bind to the province at the time of Modification
Public void databindmodprov (string prov_id)
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_prov", con );
Sqldatareader SDR = cmd. executereader ();
This. Prov. Items. Clear ();
Int I = 0;
While (SDR. Read ())
{
This. Prov. Items. insert (I, new listitem (SDR ["prov_name"]. tostring (), SDR ["prov_id"]. tostring ()));
If (prov_id = SDR ["prov_id"]. tostring ())
{
This. Prov. items [I]. Selected = true;
}
I ++;
}
SDR. Close ();
Con. Close ();
}

// Bind to the modified City
Public void databindmodcity (string prov_id, string city_id)
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_city where city_provid =" + prov_id, con );
Sqldatareader SDR = cmd. executereader ();
This. City. Items. Clear ();
Int I = 0;
While (SDR. Read ())
{
This. City. Items. insert (I, new listitem (SDR ["city_name"]. tostring (), SDR ["city_id"]. tostring ()));
If (city_id = SDR ["city_id"]. tostring ())
{
This. City. items [I]. Selected = true;
}
I ++;
}
SDR. Close ();
Con. Close ();
}

// Bind to the service station at the time of Modification
Public void databindmodservstat (string city_id, string servstat_id)
{
Sqlconnection con = dB. createsqlconneciton ();
Con. open ();
Sqlcommand cmd = new sqlcommand ("select * From t_servstat where servstat_cityid =" + city_id, con );
Sqldatareader SDR = cmd. executereader ();
This. servstat. Items. Clear ();
Int I = 0;
While (SDR. Read ())
{
This. servstat. Items. insert (I, new listitem (SDR ["servstat_name"]. tostring (), SDR ["servstat_id"]. tostring ()));
If (servstat_id = SDR ["servstat_id"]. tostring ())
{
This. servstat. items [I]. Selected = true;
}
I ++;
}
SDR. Close ();
Con. Close ();
}
}

For more information, see mine.
Note: The drop-down autopostback must be prefixed