Required Field Validator hidden in asp.net Repeater - asp.net

Question

I have reapeater in my code and trying to validate the textbox using asp.net required field validator. But validation messsage
not displaying, i opened the developer tools and found that style="visibility:hidden" added into the required field validator.
Below is my code
<asp:Repeater ID="RepeaterCategory" runat="server" DataSource='<%# this.Categories.Count==0 ? null : this.Categories %>'>
<ItemTemplate>
<div>
<asp:Label runat="server" Visible="true" Text="Category" />
<asp:PlaceHolder runat="server" Visible="true">
<asp:TextBox ID="txtCategoryID" runat="server" value="1" />
<asp:TextBox ID="txtCategoryName" runat="server" value="<%# (Container.DataItem as Category).Name %>" />
<asp:RequiredFieldValidator runat="server" ErrorMessage="<br/>This is a required field" ControlToValidate="txtCategoryName" ValidationGroup="NewCategoryGroup"></asp:RequiredFieldValidator>
</asp:PlaceHolder>
<asp:LinkButton runat="server" ToolTip="Save" ValidationGroup="NewCategoryGroup" OnClick="SaveCategory_Click"><img src='<%# some path%>/images/save.gif' /></asp:LinkButton>
<asp:LinkButton runat="server" ToolTip="Close" OnClick="CloseCategory_Click"></asp:LinkButton>
</div>
</ItemTemplate>
</asp:Repeater>
Code behind file
protected void SaveCategory_Click(object o, EventArgs e)
{
Page.Validate("NewCategoryGroup");
if (!Page.IsValid)
return;
//logic
}
Can anyone suggest how to enable it?

Answer 1

The style="visibility:hidden" is default behavior. It changes to style="visibility: visible;" when the error message needs displaying. Therefore you probably don't have an error.
The validator is a 'RequiredFieldValidator', and since the textbox that is being validated is already filled with the value "TestCategory" there are no errors. If you just add text to the Save button (which has no ID tag) so that it becomes visible, remove the value from the txtCategoryName textbox and click the save button you will see the error message.
This works:
<asp:TextBox ID="txtCategoryName" runat="server" value="" />
<asp:RequiredFieldValidator runat="server" ErrorMessage="<br/>This is a required field" ControlToValidate="txtCategoryName" ValidationGroup="NewCategoryGroup"></asp:RequiredFieldValidator>
<asp:LinkButton runat="server" ToolTip="Save" ValidationGroup="NewCategoryGroup" OnClick="SaveCategory_Click" ID="LinkButton1">Save Me!</asp:LinkButton>
You don't need this code
Page.Validate("NewCategoryGroup");
if (!Page.IsValid)
Another advantage is that the validators work now without a postback, this saves a roundtrip to the server.
And ALWAYS do server side validation also, but try to do the first validation without postback.
UPDATE
What you want is probably validation per item. And since your validationgroup is always the same it will fire for all textboxes. Try this:
<asp:Repeater ID="RepeaterCategory" runat="server">
<ItemTemplate>
<div>
<asp:TextBox ID="txtCategoryName" runat="server" ValidationGroup='<%# "myVal_" + Container.ItemIndex %>' Text='<%# Eval("Category") %>' />
<br />
<asp:RequiredFieldValidator runat="server" Display="Dynamic" ErrorMessage="This is a required field<br />" ControlToValidate="txtCategoryName" ValidationGroup='<%# "myVal_" + Container.ItemIndex %>'></asp:RequiredFieldValidator>
<asp:LinkButton runat="server" ValidationGroup='<%# "myVal_" + Container.ItemIndex %>' OnClick="Button1_Click" ID="LinkButton1">Save Me!</asp:LinkButton>
</div>
</ItemTemplate>
</asp:Repeater>