Remove previously selected text from DropDownList inside GridView using C# in ASP.Net

Hi priyatrip,

I have created sample please refe the below code.

HTML

<asp:GridView runat="server" ID="gvDetails" AutoGenerateColumns="false" OnRowDataBound="OnRowDataBound">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" Visible="false" />
        <asp:BoundField DataField="State" HeaderText="State" />
        <asp:BoundField DataField="Country" HeaderText="Country" />
        <asp:BoundField DataField="City" HeaderText="City" HtmlEncode="false" />
        <asp:TemplateField HeaderText="State Flag">
            <ItemTemplate>
                <asp:DropDownList runat="server" Width="75px" ID="ddl1" OnSelectedIndexChanged="SelectionChanged"
                    AutoPostBack="true">
                </asp:DropDownList>
                <br />
                <asp:DropDownList runat="server" Width="75px" ID="ddl2" OnSelectedIndexChanged="SelectionChanged"
                    AutoPostBack="true">
                </asp:DropDownList>
                <br />
                <asp:DropDownList runat="server" Width="75px" ID="ddl3" OnSelectedIndexChanged="SelectionChanged"
                    AutoPostBack="true">
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[] { new DataColumn("Id"), new DataColumn("State"), new DataColumn("Country"), new DataColumn("City") });
        dt.Rows.Add(1, "UP", "India", "Agra<br/>Delhi<br/>Shimla");
        dt.Rows.Add(2, "US", "America", "New york<br/>New Gercy<br/>Milan");
        dt.Rows.Add(3, "Chicago", "Illinois", "Manipolis<br/>Perth<br/>Balino");
        gvDetails.DataSource = dt;
        gvDetails.DataBind();
    }
}

protected void SelectionChanged(object sender, EventArgs e)
{
    DropDownList current = sender as DropDownList;
    GridViewRow row = current.NamingContainer as GridViewRow;
    List<DropDownList> others = new List<DropDownList>();
    foreach (Control item in row.Controls[4].Controls)
    {
        if (item.GetType() == typeof(DropDownList))
        {
            if (((DropDownList)item).ID != current.ID)
            {
                others.Add(item as DropDownList);
            }
        }
    }
    DisableSelectedText(current, others.ToArray());
}

protected void DisableSelectedText(DropDownList ddlCurrent, DropDownList[] others)
{
    foreach (DropDownList item in others)
    {
        item.Items.Remove(ddlCurrent.SelectedItem.Value);
    }
}

private DataTable GetFlag()
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Text", typeof(string)), new DataColumn("Value", typeof(int)) });
    dt.Rows.Add(1, 1);
    dt.Rows.Add(2, 2);
    dt.Rows.Add(3, 3);
    dt.Rows.Add(4, 4);
    return dt;
}

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
    DataTable dt = GetFlag();
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DropDownList ddl1 = e.Row.FindControl("ddl1") as DropDownList;
        DropDownList ddl2 = e.Row.FindControl("ddl2") as DropDownList;
        DropDownList ddl3 = e.Row.FindControl("ddl3") as DropDownList;
        ddl1.DataSource = dt;
        ddl1.DataTextField = "Text";
        ddl1.DataValueField = "Value";
        ddl1.DataBind();
        ddl2.DataSource = dt;
        ddl2.DataTextField = "Text";
        ddl2.DataValueField = "Value";
        ddl2.DataBind();
        ddl3.DataSource = dt;
        ddl3.DataTextField = "Text";
        ddl3.DataValueField = "Value";
        ddl3.DataBind();
    }
}

Screenshot