Error Handling for empty textboxes in aspnet and vbnet - asp.net

Question

I have an ADD button in my FormView in ASP.NET. And I have txtName on it that should first check if the textbox is empty. If it was empty, the ADD button should message Please fill up the form.
I tried the traditional error handling in vb.net like
If txtbox.text = "" then
error msg
end if
but it is not applicable when making a web page using ASP.NET backend: VBNET.
<asp:FormView ID="FormView1" runat="server" DataKeyNames="ID" DataSourceID="SqlDataSource1" Height="92px" Width="835px" AllowPaging="True" CellPadding="3" DefaultMode="Insert" BackColor="White" BorderColor="#E7E7FF" BorderStyle="None" BorderWidth="1px" GridLines="Horizontal" BackImageUrl= "howto.jpg" style="margin-bottom: 12px">
<EditRowStyle BackColor="#738A9C" BorderStyle="Solid" Font-Bold="True" ForeColor="#F7F7F7" />
<FooterStyle BackColor="#B5C7DE" ForeColor="#4A3C8C" />
<HeaderStyle BackColor="#4A3C8C" Font-Bold="True" ForeColor="#F7F7F7" />
<InsertItemTemplate>
<asp:Label ID="lblName" runat="server" Text="Name of Applicant" Font-Size ="10pt" Font-Names="Arial" ></asp:Label>
<asp:Label ID="lblBday" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Birthday"></asp:Label>
<asp:Label ID="Gender" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Gender"></asp:Label>
<br />
<asp:TextBox ID="txtName" runat="server" Height="19px" Text='<%# Bind("Name") %>' Width="216px" Font-Size ="10" Font-Names="Arial"></asp:TextBox>
<asp:TextBox ID="txtBday" runat="server" Font-Names="Arial" Font-Size="10pt" Height="19px" Text='<%# Bind("Birthday") %>' TextMode="Date" Width="216px"></asp:TextBox>
<asp:DropDownList ID="txtGender" runat="server" Height="19px" Width="222px" SelectedValue='<%# Bind("Gender") %>'>
<asp:ListItem>Male</asp:ListItem>
<asp:ListItem>Female</asp:ListItem>
</asp:DropDownList>
<br />
<br />
<asp:Label ID="lblAddress" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Address"></asp:Label>
<asp:Label ID="lblContact" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Contact"></asp:Label>
<br />
<asp:TextBox ID="txtAddress" runat="server" Font-Names="Arial" Font-Size="10pt" Height="19px" Text='<%# Bind("Address") %>' Width="488px"></asp:TextBox>
<asp:TextBox ID="txtContact" runat="server" Font-Names="Arial" Font-Size="10pt" Height="19px" Text='<%# Bind("Contact") %>' Width="216px"></asp:TextBox>
<br />
<br />
<br />
<asp:Label ID="lblEduc" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Educational Attainment"></asp:Label>
<asp:Label ID="lblCourse" runat="server" Font-Names="Arial" Font-Size="10pt" Text="Course"></asp:Label>
<br />
<asp:DropDownList ID="txtEduc" runat="server" Height="19px" SelectedValue='<%# Bind("Education") %>' Width="495px">
<asp:ListItem>High School</asp:ListItem>
<asp:ListItem>College Diploma (2-3 years)</asp:ListItem>
<asp:ListItem>College Undergrad (4-5 years)</asp:ListItem>
<asp:ListItem>Bachelor's Degree</asp:ListItem>
<asp:ListItem Value="Master">Masteral</asp:ListItem>
<asp:ListItem>Doctor</asp:ListItem>
</asp:DropDownList>
<asp:TextBox ID="txtCourse" runat="server" Font-Names="Arial" Font-Size="10pt" Height="19px" Text='<%# Bind("Course") %>' Width="216px"></asp:TextBox>
<br />
<br />
<br />
<asp:Button ID="btnAdd" runat="server" Text="ADD" Font-Bold="True" Font-Size="Medium" ForeColor="Black" BorderColor="Black" BorderStyle="Solid" BorderWidth="2px" CausesValidation="True" ValidationGroup="Insert" Font-Names="Berlin Sans FB Demi" CommandName="Insert" />
<asp:Button ID="btnCancel" runat="server" Text="CANCEL" Font-Bold="True" Font-Names="Berlin Sans FB Demi" Font-Size="Medium" ForeColor="Black" BorderColor="Black" BorderStyle="Solid" BorderWidth="2px" CommandName="Cancel" />
</InsertItemTemplate>
<PagerStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" HorizontalAlign="Right" />
<RowStyle BackColor="#E7E7FF" ForeColor="#4A3C8C" />
</asp:FormView>

Answer 1

You can't show that alert on a webapp, but you can use javascript in order to do it.
In code behind declare this function:
Public Sub AlertMessage(ByVal mensaje As String, ByVal pag As Page)
pag.ClientScript.RegisterStartupScript(Me.GetType(), "showConfirm", "Alerta('" & mensaje & "');", True)
End Sub
Then call it from your ADD button like this:
If txtbox.text = "" then
AlertMessage(msg, Me.Page)
end if
Hope this helps

Answer 2

I've learn from some research that there is other way for error handling using ASPNET. I used the validation control and validation group.
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" ValidationGroup ="FillUp" runat="server" ControlToValidate ="txtName" ErrorMessage="Please Enter Your Name"></asp:RequiredFieldValidator><br />
<asp:Button ID="btnAdd" runat="server" Text="ADD" Font-Bold="True" Font-Size="Medium" ForeColor="Black" BorderColor="Black" BorderStyle="Solid" BorderWidth="2px" CausesValidation="True" ValidationGroup="FillUp" Font-Names="Berlin Sans FB Demi" CommandName="Insert" />
enter image description here
I also add this code in my Web.config
<appSettings>
<add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />
</appSettings>
I know, what you are thinking,"This guy has a poor desig", lol, well the important is you know the code xD