Pass selected value from DropDownList to TextBox inside GridView in ASP.Net

Hi sbatcha,

I have created sample that full-fill your requirement.

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:TemplateField HeaderText="Country Name">
            <ItemTemplate>
                <asp:TextBox runat="server" ID="txtCountry" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Country">
            <ItemTemplate>
                <asp:DropDownList ID="ddlCountry" runat="server" AutoPostBack="true" OnSelectedIndexChanged="SelectedIndexChanged">
                    <asp:ListItem Text="Select" />
                    <asp:ListItem Text="India" />
                    <asp:ListItem Text="Saudi Arabia" />
                    <asp:ListItem Text="USA" />
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[1] { new DataColumn("Id") });
        dt.Rows.Add(1);
        dt.Rows.Add(2);
        dt.Rows.Add(3);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

protected void SelectedIndexChanged(object sender, EventArgs e)
{
    DropDownList ddl = sender as DropDownList;
    string selectedText = ddl.SelectedItem.Text;
    TextBox txt = ddl.NamingContainer.FindControl("txtCountry") as TextBox;
    txt.Text = selectedText;
}

Screenshot