Validate TextBox inside ASP.Net GridView based on DropDownList using C# and VB.Net

Hi sharib42,

Refer below sample code

HTML

<div>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField DataField="Item" HeaderText="Item" />
            <asp:TemplateField HeaderText="Price">
                <ItemTemplate>
                    <asp:DropDownList ID="ddl1" runat="server" class="form-select">
                        <asp:ListItem Text="Select Status" Value=""></asp:ListItem>
                        <asp:ListItem Text="Yes" Value="Yes"></asp:ListItem>
                        <asp:ListItem Text="No" Value="No"></asp:ListItem>
                    </asp:DropDownList>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Quantity">
                <ItemTemplate>
                    <asp:TextBox ID="txtQuantity" runat="server"></asp:TextBox><br />
                    <asp:RequiredFieldValidator ID="rfvQuantity" ControlToValidate="txtQuantity" runat="server"
                        ErrorMessage="Required" ForeColor="Red" Enabled="false" Display="Dynamic"></asp:RequiredFieldValidator>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <br />
    <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="OnSubmit" />
</div>

Namespace

C#

using System.Data;

VB.Net

Imports System.Data

CODE

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Item"), new DataColumn("Price"), new DataColumn("Quantity") });
        dt.Rows.Add("Shirt");
        dt.Rows.Add("Football", 299, 10);
        dt.Rows.Add("Shirt", 545, 15);
        dt.Rows.Add("Disc", 99, 20);
        dt.Rows.Add("Watch", 200, 45);
        dt.Rows.Add("Clock", 670, 97);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

protected void OnSubmit(object sender, EventArgs e)
{
    foreach (GridViewRow row in GridView1.Rows)
    {
        TextBox t_txt = (TextBox)row.FindControl("txtPrice");
        DropDownList ddl1 = (DropDownList)row.FindControl("ddl1");
        RequiredFieldValidator rfvQuantity = (RequiredFieldValidator)row.FindControl("rfvQuantity");
        string sp_ddl1 = ddl1.SelectedValue;
        if (sp_ddl1 == "Yes")
        {
            rfvQuantity.Enabled = true;
        }
        else
        {
            rfvQuantity.Enabled = false;
        }
    }       
}

VB.Net 

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {New DataColumn("Item"), New DataColumn("Price"), New DataColumn("Quantity")})
        dt.Rows.Add("Shirt")
        dt.Rows.Add("Football", 299, 10)
        dt.Rows.Add("Shirt", 545, 15)
        dt.Rows.Add("Disc", 99, 20)
        dt.Rows.Add("Watch", 200, 45)
        dt.Rows.Add("Clock", 670, 97)
        GridView1.DataSource = dt
        GridView1.DataBind()
    End If
End Sub

Protected Sub OnSubmit(ByVal sender As Object, ByVal e As EventArgs) Handles btnSubmit.Click
    For Each row As GridViewRow In GridView1.Rows
        Dim t_txt As TextBox = CType(row.FindControl("txtPrice"), TextBox)
        Dim ddl1 As DropDownList = CType(row.FindControl("ddl1"), DropDownList)
        Dim rfvQuantity As RequiredFieldValidator = CType(row.FindControl("rfvQuantity"), RequiredFieldValidator)
        Dim sp_ddl1 As String = ddl1.SelectedValue
        If sp_ddl1 = "Yes" Then
            rfvQuantity.Enabled = True
        Else
            rfvQuantity.Enabled = False
        End If
    Next
End Sub

Screenshot