Set DropDownList Selected Value inside GridView based on another Column using C# and VB.Net in ASP.Net

Hi Mohd.Mekki,

I have created a sample please take its reference and correct your code.

Database

I have made use of the following table Customers with the schema as follows.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML

<asp:GridView runat="server" ID="gvCustomers" AutoGenerateColumns="false" OnRowDataBound="OnDataBound">
    <Columns>
        <asp:BoundField DataField="CustomerID" HeaderText="ID" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:DropDownList runat="server" ID="ddlCountries">
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

C#

using System.Configuration;
using System.Data;
using System.Data.SqlClient;

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["conString"].ConnectionString))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT CustomerID,Name FROM Customers", con))
            {
                cmd.CommandType = CommandType.Text;
                using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
                {
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    this.gvCustomers.DataSource = dt;
                    this.gvCustomers.DataBind();
                }
            }
        }
    }
}
protected void OnDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        string country = "";
        string customerId = e.Row.Cells[0].Text;
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["conString"].ConnectionString))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT Country FROM Customers WHERE CustomerID=@Id", con))
            {
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@Id", customerId);
                con.Open();
                country = Convert.ToString(cmd.ExecuteScalar());
                con.Close();
            }
        }

        DropDownList ddlCountries = e.Row.FindControl("ddlCountries") as DropDownList;
        using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["conString"].ConnectionString))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT DISTINCT Country FROM Customers", con))
            {
                cmd.CommandType = CommandType.Text;
                using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
                {
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    ddlCountries.DataSource = dt;
                    ddlCountries.DataTextField = "Country";
                    ddlCountries.DataValueField = "Country";
                    ddlCountries.DataBind();
                    if (!string.IsNullOrEmpty(country))
                    {
                        if (ddlCountries.Items.FindByText(country) != null)
                        {
                            ddlCountries.Items.FindByText(country).Selected = true;
                        }
                    }
                }
            }
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Using con As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("conString").ConnectionString)
            Using cmd As SqlCommand = New SqlCommand("SELECT CustomerID,Name FROM Customers", con)
                cmd.CommandType = CommandType.Text
                Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                    Dim dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    Me.gvCustomers.DataSource = dt
                    Me.gvCustomers.DataBind()
                End Using
            End Using
        End Using
    End If
End Sub

Protected Sub OnDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
    If e.Row.RowType = DataControlRowType.DataRow Then
        Dim country As String = ""
        Dim customerId As String = e.Row.Cells(0).Text
        Using con As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("conString").ConnectionString)
            Using cmd As SqlCommand = New SqlCommand("SELECT Country FROM Customers WHERE CustomerID=@Id", con)
                cmd.CommandType = CommandType.Text
                cmd.Parameters.AddWithValue("@Id", customerId)
                con.Open()
                country = Convert.ToString(cmd.ExecuteScalar())
                con.Close()
            End Using
        End Using

        Dim ddlCountries As DropDownList = TryCast(e.Row.FindControl("ddlCountries"), DropDownList)
        Using con As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("conString").ConnectionString)
            Using cmd As SqlCommand = New SqlCommand("SELECT DISTINCT Country FROM Customers", con)
                cmd.CommandType = CommandType.Text
                Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                    Dim dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    ddlCountries.DataSource = dt
                    ddlCountries.DataTextField = "Country"
                    ddlCountries.DataValueField = "Country"
                    ddlCountries.DataBind()
                    If Not String.IsNullOrEmpty(country) Then
                        If ddlCountries.Items.FindByText(country) IsNot Nothing Then
                            ddlCountries.Items.FindByText(country).Selected = True
                        End If
                    End If
                End Using
            End Using
        End Using
    End If
End Sub

Screenshot