尝试更改asp.net中默认login.aspx页内的标签文本

Question

I am trying to change the text of a label I have created inside the default login.aspx page that is given to you when you create a new website in .net 4.0. I cannot seem to access this label in any way. The text is supposed to change when the log in button is clicked if the user is not approved. Here is where the label is made.

    <LayoutTemplate>
        <span class="failureNotification">
            <asp:Literal ID="FailureText" runat="server"></asp:Literal>
        </span>
        <asp:ValidationSummary ID="LoginUserValidationSummary" runat="server" CssClass="failureNotification" 
             ValidationGroup="LoginUserValidationGroup"/>
             <%-- If the account is not approved display an error message --%>
        <asp:Label ID="NotAproved" runat="server" CssClass="failureNotification"></asp:Label>......

I have tried to access it by using FindControl but it never works so I might be doing something wrong. Thank you in advance for your help.

EDIT: I found the way to access it in the code behind and here it is in case anyone has a similar question:

    var notApproved = (Label)LoginUser.FindControl("NotApproved");
    notApproved.Text = "Sorry Your Account has not yet Been Approved by an Administrator. Try Again Later.";

Answer 1

The FindControl method will only find server side controls (as in this case) that are direct descendants of the container you are searching. From MSDN (I have added emphasis)-

Use FindControl to access a control from a function in a code-behind page, to access a control that is inside another container, or in other circumstances where the target control is not directly accessible to the caller. This method will find a control only if the control is directly contained by the specified container; that is, the method does not search throughout a hierarchy of controls within controls. For information about how to find a control when you do not know its immediate container, see How to: Access Server Controls by ID.

http://msdn.microsoft.com/en-us/library/486wc64h.aspx

Generally you should avoid using FindControl and reference the control directly using the ID in order to return the strongly typed object and avoid a tight dependency on a particular control hierarchy, but this isn't possible for controls added within templates as you have probably found.

It seems you have either stumbled upon or worked out the direct descendent requirement by yourself, but I would suggest the following may be safer code-

var notApproved = LoginUser.FindControl("NotApproved") as Label;
if (notApproved != null)
{
    notApproved.Text = "Sorry Your Account has not yet Been Approved by an Administrator. Try Again Later.";
}

This deals with the NullReferenceException you would get if LoginUser.FindControl("NotApproved") doesn't find anything and returns Null (see the above MSDN link) and also a possible type cast exception where the object found is not a label and cannot be cast to one.