Populate Cascading DropDownList On Selection ASP.NET

Populate Cascading DropDownList In Asp.Net C# VB.NET Based On Selection Of Other DropDown In SelectedIndexChanged Event. binding state DropDown based on selection of Country DropDownlist and then populating Cities on selection of State.

There are several situations where we need to populate second or third dropdownlist list based on selection of first or second dropdwonlist in asp.net.

For this we need to write code in code behind in the SelectedIndexChanged Event of respective Dropdownlist to implement the cascading of DropDowns.

HTML SOURCE OF PAGE

   1:  <form id="form1" runat="server">

   2:  <div>

   3:  <table><tr>

   4:  <td><strong>Country :</strong></td>

   5:  <td><asp:DropDownList ID="ddlCountry" runat="server"

   6:                        AutoPostBack="True" 

   7:                        onselectedindexchanged=

   8:                   "ddlCountry_SelectedIndexChanged">

   9:      </asp:DropDownList>

  10:  </td>

  11:   

  12:  <td><strong>State:</strong></td>

  13:  <td><asp:DropDownList ID="ddlState" runat="server" 

  14:                        AutoPostBack="True" 

  15:                        onselectedindexchanged=

  16:                   "ddlState_SelectedIndexChanged">

  17:      </asp:DropDownList></td>

  18:   

  19:  <td><strong>City:</strong></td>

  20:  <td><asp:DropDownList ID="ddlCity" runat="server" 

  21:                        AutoPostBack="True">

  22:      </asp:DropDownList></td>

  23:  </tr>

  24:  <tr><td><asp:Label ID="lblMsg" runat="server">

  25:         </asp:Label>

  26:      </td>

  27:  </tr>  

  28:  </table>

  29:   </div>

  30:   </form>

Write following code in respective events of page and dropdownlists.

C# CODE

---

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillCountry();
        }
    }
    protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
    {
        int CountryID = Convert.ToInt32(ddlCountry.SelectedValue.ToString());
        FillStates(CountryID);
        ddlCity.SelectedIndex = 0;
    }
    protected void ddlState_SelectedIndexChanged(object sender, EventArgs e)
    {
        int StateID = Convert.ToInt32(ddlState.SelectedValue.ToString());
        FillCities(StateID);
    }

    private void FillCountry()
    {
        string strConn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection con = new SqlConnection(strConn);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT CountryID, CountryName FROM Country";
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;
        con.Open();
        dAdapter.Fill(objDs);
        con.Close();
        if (objDs.Tables[0].Rows.Count > 0)
        {
            ddlCountry.DataSource = objDs.Tables[0];
            ddlCountry.DataTextField = "CountryName";
            ddlCountry.DataValueField = "CountryID";
            ddlCountry.DataBind();
            ddlCountry.Items.Insert(0, "--Select--");
        }
        else
        {
            lblMsg.Text = "No Countries found";
        }
    }

    private void FillStates(int countryID)
    {
        string strConn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection con = new SqlConnection(strConn);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT StateID, StateName FROM State WHERE CountryID =@CountryID";
        cmd.Parameters.AddWithValue("@CountryID", countryID);
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;
        con.Open();
        dAdapter.Fill(objDs);
        con.Close();
        if (objDs.Tables[0].Rows.Count > 0)
        {
            ddlState.DataSource = objDs.Tables[0];
            ddlState.DataTextField = "StateName";
            ddlState.DataValueField = "StateID";
            ddlState.DataBind();
            ddlState.Items.Insert(0, "--Select--");
        }
        else
        {
            lblMsg.Text = "No states found";
        }
    }

    private void FillCities(int stateID)
    {
        string strConn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection con = new SqlConnection(strConn);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT CityID, CityName FROM City WHERE StateID =@StateID";
        cmd.Parameters.AddWithValue("@StateID", stateID);
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;
        con.Open();
        dAdapter.Fill(objDs);
        con.Close();
        if (objDs.Tables[0].Rows.Count > 0)
        {
            ddlCity.DataSource = objDs.Tables[0];
            ddlCity.DataTextField = "CityName";
            ddlCity.DataValueField = "CItyID";
            ddlCity.DataBind();
            ddlCity.Items.Insert(0, "--Select--");
        }
        else
        {
            lblMsg.Text = "No Cities found";
        }
    }

VB.NET

---

Protected Sub Page_Load(sender As Object, e As EventArgs)
 If Not IsPostBack Then
  FillCountry()
 End If
End Sub
Protected Sub ddlCountry_SelectedIndexChanged(sender As Object, e As EventArgs)
 Dim CountryID As Integer = Convert.ToInt32(ddlCountry.SelectedValue.ToString())
 FillStates(CountryID)
 ddlCity.SelectedIndex = 0
End Sub
Protected Sub ddlState_SelectedIndexChanged(sender As Object, e As EventArgs)
 Dim StateID As Integer = Convert.ToInt32(ddlState.SelectedValue.ToString())
 FillCities(StateID)
End Sub

Private Sub FillCountry()
 Dim strConn As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
 Dim con As New SqlConnection(strConn)
 Dim cmd As New SqlCommand()
 cmd.Connection = con
 cmd.CommandType = CommandType.Text
 cmd.CommandText = "SELECT CountryID, CountryName FROM Country"
 Dim objDs As New DataSet()
 Dim dAdapter As New SqlDataAdapter()
 dAdapter.SelectCommand = cmd
 con.Open()
 dAdapter.Fill(objDs)
 con.Close()
 If objDs.Tables(0).Rows.Count > 0 Then
  ddlCountry.DataSource = objDs.Tables(0)
  ddlCountry.DataTextField = "CountryName"
  ddlCountry.DataValueField = "CountryID"
  ddlCountry.DataBind()
  ddlCountry.Items.Insert(0, "--Select--")
 Else
  lblMsg.Text = "No Countries found"
 End If
End Sub

Private Sub FillStates(countryID As Integer)
 Dim strConn As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
 Dim con As New SqlConnection(strConn)
 Dim cmd As New SqlCommand()
 cmd.Connection = con
 cmd.CommandType = CommandType.Text
 cmd.CommandText = "SELECT StateID, StateName FROM State WHERE CountryID =@CountryID"
 cmd.Parameters.AddWithValue("@CountryID", countryID)
 Dim objDs As New DataSet()
 Dim dAdapter As New SqlDataAdapter()
 dAdapter.SelectCommand = cmd
 con.Open()
 dAdapter.Fill(objDs)
 con.Close()
 If objDs.Tables(0).Rows.Count > 0 Then
  ddlState.DataSource = objDs.Tables(0)
  ddlState.DataTextField = "StateName"
  ddlState.DataValueField = "StateID"
  ddlState.DataBind()
  ddlState.Items.Insert(0, "--Select--")
 Else
  lblMsg.Text = "No states found"
 End If
End Sub

Private Sub FillCities(stateID As Integer)
 Dim strConn As String = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
 Dim con As New SqlConnection(strConn)
 Dim cmd As New SqlCommand()
 cmd.Connection = con
 cmd.CommandType = CommandType.Text
 cmd.CommandText = "SELECT CityID, CityName FROM City WHERE StateID =@StateID"
 cmd.Parameters.AddWithValue("@StateID", stateID)
 Dim objDs As New DataSet()
 Dim dAdapter As New SqlDataAdapter()
 dAdapter.SelectCommand = cmd
 con.Open()
 dAdapter.Fill(objDs)
 con.Close()
 If objDs.Tables(0).Rows.Count > 0 Then
  ddlCity.DataSource = objDs.Tables(0)
  ddlCity.DataTextField = "CityName"
  ddlCity.DataValueField = "CItyID"
  ddlCity.DataBind()
  ddlCity.Items.Insert(0, "--Select--")
 Else
  lblMsg.Text = "No Cities found"
 End If
End Sub

Build and run the code.

Download Sample Code