Enable Disable ChackBox based on DropDownList inside ASP.Net GridView using C# and VB.Net

Hi BugHunter,

Refer below sample.

HTML

<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false" OnRowDataBound="OnRowDataBound"
    DataKeyNames="CustomerId">
    <Columns>
        <asp:BoundField DataField="ContactName" HeaderText="ContactName" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:CheckBox ID="CheckBox1" runat="server" Enabled="false" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Country" ItemStyle-Width="150">
            <ItemTemplate>
                <asp:DropDownList ID="ddlCountries" runat="server" AutoPostBack="true" OnSelectedIndexChanged="EnableDisableCheckBox">
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

C#

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

VB.Net

Imports System.Data.SqlClient
Imports System.Data

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.BindGrid();
    }
}

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        SqlCommand cmd = new SqlCommand("SELECT DISTINCT(Country) FROM Customers");
        DropDownList ddlCountries = (e.Row.FindControl("ddlCountries") as DropDownList);
        ddlCountries.DataSource = this.ExecuteQuery(cmd);
        ddlCountries.DataTextField = "Country";
        ddlCountries.DataValueField = "Country";
        ddlCountries.DataBind();
        ddlCountries.Items.Insert(0, new ListItem("Please select"));
    }
}

private void BindGrid()
{
    SqlCommand cmd = new SqlCommand("SELECT TOP 5 CustomerId, ContactName, Country FROM Customers");
    gvCustomers.DataSource = this.ExecuteQuery(cmd);
    gvCustomers.DataBind();
}

private DataTable ExecuteQuery(SqlCommand cmd)
{
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(conString))
    {
        cmd.Connection = con;

        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            sda.SelectCommand = cmd;
            using (DataTable dt = new DataTable())
            {
                sda.Fill(dt);
                return dt;
            }
        }
    }
}
protected void EnableDisableCheckBox(object sender, EventArgs e)
{
    foreach (GridViewRow row in gvCustomers.Rows)
    {
        DropDownList ddl = row.FindControl("ddlCountries") as DropDownList;
        CheckBox chk = row.FindControl("CheckBox1") as CheckBox;
        if (ddl.SelectedIndex > 0)
        {
            chk.Enabled = true;
        }
        else
        {
            chk.Enabled = false;
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        Me.BindGrid()
    End If
End Sub

Protected Sub OnRowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
    If e.Row.RowType = DataControlRowType.DataRow Then
        Dim cmd As SqlCommand = New SqlCommand("SELECT DISTINCT(Country) FROM Customers")
        Dim ddlCountries As DropDownList = (TryCast(e.Row.FindControl("ddlCountries"), DropDownList))
        ddlCountries.DataSource = Me.ExecuteQuery(cmd)
        ddlCountries.DataTextField = "Country"
        ddlCountries.DataValueField = "Country"
        ddlCountries.DataBind()
        ddlCountries.Items.Insert(0, New ListItem("Please select"))
    End If
End Sub

Private Sub BindGrid()
    Dim cmd As SqlCommand = New SqlCommand("SELECT TOP 5 CustomerId, ContactName, Country FROM Customers")
    gvCustomers.DataSource = Me.ExecuteQuery(cmd)
    gvCustomers.DataBind()
End Sub

Private Function ExecuteQuery(ByVal cmd As SqlCommand) As DataTable
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(conString)
        cmd.Connection = con
        Using sda As SqlDataAdapter = New SqlDataAdapter()
            sda.SelectCommand = cmd
            Using dt As DataTable = New DataTable()
                sda.Fill(dt)
                Return dt
            End Using
        End Using
    End Using
End Function
Protected Sub EnableDisableCheckBox(ByVal sender As Object, ByVal e As EventArgs)
    For Each row As GridViewRow In gvCustomers.Rows
        Dim ddl As DropDownList = TryCast(row.FindControl("ddlCountries"), DropDownList)
        Dim chk As CheckBox = TryCast(row.FindControl("CheckBox1"), CheckBox)

        If ddl.SelectedIndex > 0 Then
            chk.Enabled = True
        Else
            chk.Enabled = False
        End If
    Next
End Sub

Screenshot