Validate empty TextBox on ASP.Net CustomValidator ServerValidate event using C# and VB.Net

Hi irshad1231,

Since ControlToValidate is assigned as TextBox, CustomValidator will only fire when the TextBox is not empty.

So the work around for this is to set CustomValidator ValidateEmptyText property to true.

Check this example. Now please take its reference and correct your code.

For demonstration i have used TextBox instead of Label.

HTML

<asp:TextBox runat="server" ID="lbl_iscitizen" Text="true" /><br />
<%--<asp:Label ID="lbl_iscitizen" runat="server" Text="true"></asp:Label>--%>
<asp:TextBox ID="lbl_iqamaexpiry" runat="server" Text="" CssClass="textboxAslabel"></asp:TextBox>
<asp:CustomValidator ID="cv_name" runat="server" ControlToValidate="lbl_iqamaexpiry"
 Text="Required" ValidateEmptyText="true" OnServerValidate="cv_name_ServerValidate"
 ValidationGroup="validate" ForeColor="Red"></asp:CustomValidator><br />
<asp:Button ID="submitButton" runat="server" OnClick="submitButton_Click" Text="Submit"
 ValidationGroup="validate" />

C#

protected void cv_name_ServerValidate(object source, ServerValidateEventArgs args)
{
    if (lbl_iscitizen.Text.ToLower() == "true")
    {
        args.IsValid = true;
    }
    else
    {
        args.IsValid = false;
    }
}

protected void submitButton_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        submitButton.Text = "Valid";
    }
    else
    {
        submitButton.Text = "Invalid!";
    }
}

VB.Net

Protected Sub cv_name_ServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)
    If lbl_iscitizen.Text.ToLower() = "true" Then
        args.IsValid = True
    Else
        args.IsValid = False
    End If
End Sub

Protected Sub submitButton_Click(ByVal sender As Object, ByVal e As EventArgs)
    If Page.IsValid Then
        submitButton.Text = "Valid"
    Else
        submitButton.Text = "Invalid!"
    End If
End Sub

Screenshot