How to dynamically change Master pages?

T. R. Tinker · December 29th, 2009, 04:32 AM

I'm trying to add this into an application I've already written, and am stuck.

I have two master pages: default.master and alternate.master. I would like to allow a user to switch back-and-forth between the two master pages as often as they want - the master pages yield two very different designs.

I have a BasePage class.

I add the links/linkbuttons to the master pages from a *.ascx file with it's own codefile.

Somewhere in all of this, I can't figure out where I handle changing the master pages.

In the .ascx file, I am using LinkButtons (for the moment):

Code:

<asp:Linkbutton id="btnDefault" commandArgument="default" onCommand="Change_Master" causesValidation="false" text="DEFAULT SKIN" runat='server'/>

and:

Code:

<asp:Linkbutton id="btnAlternate" commandArgument="alternate" onCommand="Change_Master" causesValidation="false" text="ALTERNATE SKIN" runat='server'/>

In the codefule for the .ascx, I am using this:

Code:

 
protected void Change_Master (object sender, CommandEventArgs e)
{
Session["Page_Master"] = e.CommandArgument.ToString();
this.Response.Redirect(this.Request.Url.ToString());
}

In the individual page classes, I can detect and display the content of the Session["Page_Master"] object in the OnLoad event, but cannot detect it in the OnPreInit event. In the OnPreInit event, if I try to apply the session object to change the page master, I get a 404 error for a page dependency not found.

I don't know if the BasePage class has a role to play, what it should be doing in the BasePage_PreInit event, or if I handle it all within the individual page classes...

I have tinkered with this for so long I have completely confused myself, and would appreciate any help or guidance in how to untangle this Gordian knot.

Thanks, and Happy New Year!

- Tinker

Imar · December 29th, 2009, 02:56 PM

Hi there,

PreInit is indeed the place. Here's some sample code (VB) from a BasePage class in an app where it works:

Code:

 Protected Overrides Sub OnPreInit(ByVal e As EventArgs)
  Dim myHostHeader As String = Me.HostHeader.ToLower().Replace(".test", "")
    Select Case myHostHeader
      Case "SomeSite"
        Me.MasterPageFile = Me.MasterPageFile.Replace("/MasterPages/", "/MasterPages/SomeMasterPage/")
      Case "SomeOtherSite"
        Me.MasterPageFile = Me.MasterPageFile.Replace("/MasterPages/", "/MasterPages/SomeOtherMasterPage/")
    End Select
    MyBase.OnPreInit(e)
End Sub

Not sure what you mean with "I get a 404 error for a page dependency not found." though...

Cheers,

Imar

chroniclemaster1 · December 29th, 2009, 06:15 PM

Quote:

Originally Posted by Imar

Not sure what you mean with "I get a 404 error for a page dependency not found." though...

I would guess that the path to one or both of the master pages is incorrect. If you're adapting Imar's code sample, you'll be defining the path differently which "should" take care of the problem. I wouldn't worry about it for now. The alternative is to confirm if the master pages are really in the correct path location.

T. R. Tinker · December 30th, 2009, 04:44 AM

Thank you, Imar.

With very minor changes to adapt to my site's folder/directory structure, this is now working.

I first saw the "404" error when I started using .Net 3.5 and IE8, and the code for a dynamically-created control failed. I looked at the URL for the longest time until I was certain it was correct before I found the bug in my code. So it seems that if the page is incomplete, .Net 3.5 and IE8 will toss that kind of cryptic 404 error with the added sentence that a "page dependency might not have loaded or has been moved."

Thanks.

Imar · December 30th, 2009, 07:01 AM

BTW, this line:

Dim myHostHeader As String = Me.HostHeader.ToLower().Replace(".test", "")
could be rewritten as

Dim myHostHeader As String = Me.HostHeader.ToLower()

or

Dim myHostHeader As String = Request.ServerVariables("HTTP_HOST")

The HostHeader property is local to the BasePage class and returns Request.ServerVariables("HTTP_HOST") with the port number and colon stripped off the path.

We used fake .test domain extensions in the environment so we needed to strip that off to make it a real domain.

Clearly, how you determine which Master Page to load is entirely up to you. I used the current host header, but you can use whatever you see fit (sessions, cookiies etc).

Cheers,

Imar