Hi guys,
Here's my scenario. I have two buttons on the master page. A search button and a Login button. The search button is on the form, the login button is inside the loginview control which is also inside the form.
I tried to set the login button as the default button by using the following code:

Dim loginView As LoginView = DirectCast(Master.FindControl("LoginView1"), LoginView)
Dim btnLogin As Button = DirectCast(loginView.FindControl("LoginButton"), Button)
Me.Page.Form.DefaultButton = btnLogin.UniqueID

I run the above code under the page load event for the defaultpage for trial. Instead of getting it to work, I got this error:

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 5:      Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Line 6:          Dim loginView As LoginView = DirectCast(Master.FindControl("LoginView1"), LoginView)
Line 7:          Dim btnLogin As Button = DirectCast(loginView.FindControl("LoginButton"), Button)
Line 8:  
Line 9:          Me.Page.Form.DefaultButton = btnLogin.UniqueID

All helps are appreciated. Thanks

Are you using the LoginView purely to hide the menu once users have logged in? If so, you may just prefer to set the VisibleWhenLoggedIn property of the Login control to true. This means you can move the Login control outside of the LoginView and won't have any trouble setting the default button on the form declaratively.

Yeah, I set the code for the default button on the code behind for the content page.

Now, what is the syntax for setting default button on the form tag if the my login button has ID="LoginButton" and it's inside the LoginView control with ID="LoginView1"

I tried <form id="form1" runat="server" defaultbutton="LoginButton"> on the master page, but when I run it, I got the following error:

[InvalidOperationException: The DefaultButton of 'form1' must be the ID of a control of type IButtonControl.]
   System.Web.UI.HtmlControls.HtmlForm.RenderAttributes(HtmlTextWriter writer) +1356
   System.Web.UI.HtmlControls.HtmlControl.RenderBeginTag(HtmlTextWriter writer) +39
   System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +56
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +25
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +121
   System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +37
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +199
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +20
   System.Web.UI.Control.Render(HtmlTextWriter writer) +7
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +25
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +121
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +22
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +199
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +20
   System.Web.UI.Control.Render(HtmlTextWriter writer) +7
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +25
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +121
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +22
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +199
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +20
   System.Web.UI.Page.Render(HtmlTextWriter writer) +26
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +25
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +121
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +22
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2558

You can't set the DefaultButton because the button is within a template and therefore doesn't exist until the template is generated. Also, when the user is logged in, the LoginTemplate is not visible, so the LoginButton wouldn't exist and you'd get the same exception.

You're best bet is to not use a LoginView for this particular scenario; just have the LoginButton on the page, the same as the search button, and control it within code. Something like this (not tested):

If Not Page.IsPostBack Then

  If Not HttpContext.Current.User.Identity.IsAuthenticated Then

    LoginButton.Visible = True

   Page.Form.DefaultButton = "LoginButton"

  Else

    LoginButton.Visible = False 

  End If

End If