Validate Grouped CheckBoxes on ASP.Net Button Click using C# and VB.Net

Hi RichardSa,

Refer below code.

HTML

<asp:CheckBox ID="CheckBox1" runat="server" AutoPostBack="true" />Mango
<asp:CustomValidator ID="question1" runat="server" Display="Dynamic" ErrorMessage="Please Choose"
    OnServerValidate="OnServerValidate" ValidationGroup="ProductCheck" ForeColor="Red"></asp:CustomValidator>
<br />
<asp:CheckBox ID="CheckBox2" runat="server" AutoPostBack="true" />Apple
<asp:CustomValidator ID="CustomValidator1" runat="server" Display="Dynamic" ErrorMessage="Please Choose"
    OnServerValidate="OnServerValidate" ValidationGroup="ProductCheck" ForeColor="Red"></asp:CustomValidator>
<br />
<asp:CheckBox ID="CheckBox3" runat="server" AutoPostBack="true" />Orange 
<asp:CustomValidator ID="CustomValidator2" runat="server" Display="Dynamic" ErrorMessage="Please Choose"
    OnServerValidate="OnServerValidate" ValidationGroup="ProductCheck" ForeColor="Red"></asp:CustomValidator>
<br />
<asp:Button Text="Save" runat="server" OnClick="OnSave" ValidationGroup="ProductCheck" />

Code

C#

protected void OnServerValidate(object source, ServerValidateEventArgs args)
{
    args.IsValid = CheckBox1.Checked || CheckBox2.Checked || CheckBox3.Checked;
}

protected void OnSave(object sender, EventArgs e)
{
    if (Page.IsValid)
    {

    }
}

VB.Net

Protected Sub OnServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)
    args.IsValid = CheckBox1.Checked OrElse CheckBox2.Checked OrElse CheckBox3.Checked
End Sub

Protected Sub OnSave(ByVal sender As Object, ByVal e As EventArgs)
    If Page.IsValid Then
    End If
End Sub