Inheritance and Nested Master Pages

Download source - 16.6 KB

Introduction

This article is about small problem I got stuck when I tried to use inheritance with Nested Master Pages. If you looking for something general about Master Pages please try to see this article Inside Master Pages

Problem description

Well, here is my situation

Screenshot - NestedMasterPages.gif

As you can see I try to inherit Child.Master from Main.Master and then use Child.Master in MyPage.

Main.master

<%@ Master Language="C#" AutoEventWireup="true" 
    CodeBehind="Main.master.cs" Inherits="Master.Main" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" 
       "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head id="mainHead" runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="mainForm" runat="server">
        <asp:Literal ID="TopMessageLiteral" runat="server" />
        
        <div id="content">           
            <asp:contentplaceholder id="cphMain" runat="server" />
    </div>
    </form>
</body>
</html>

Child.master

<%@ Master Language="C#" MasterPageFile="~/Master/Main.master" AutoEventWireup="true" 
    CodeBehind="Child.master.cs" Inherits="Master.Child" %>
<%@ MasterType VirtualPath="~/Master/Main.master" %>
<asp:Content ID="cntMain" ContentPlaceHolderID="cphMain" Runat="Server">
    <div id="left">       
        <asp:contentplaceholder id="cphLeftCol" runat="server" />
    </div>  
    
    <div id="right">
        <asp:contentplaceholder id="cphRightCol" runat="server" />    
    </div>
</asp:Content>

MyPage

<%@ Page Language="C#" MasterPageFile="~/Master/Child.master" AutoEventWireup="true" 
    Inherits="MyPage" Title="Untitled Page" Codebehind="MyPage.aspx.cs" %>
<%@ MasterType VirtualPath="~/Master/Child.master" %>

<asp:Content ID="cntLeftCol" ContentPlaceHolderID="cphLeftCol" Runat="Server">
    <p>test left</p>
</asp:Content>
<asp:Content ID="cntRightCol" ContentPlaceHolderID="cphRightCol" Runat="Server">
    <p>test right</p>
</asp:Content>

Code-behinds please see below:

//Main.master
//-------------
public partial class Main : System.Web.UI.MasterPage {
  
  private string _topMessage;

  public string TopMessage {
    get { return _topMessage; }
    set { _topMessage = value; }
  }

  protected void Page_Load(object sender, EventArgs e) {
    TopMessageLiteral.Text = TopMessage;
  }
}

//Child.master 
//------------
public partial class Child : Main {

   protected new void Page_Load(object sender, EventArgs e) {
               
   }

}

//MyPage.aspx 
//----------
public partial class MyPage: System.Web.UI.Page {

  protected void Page_Load(object sender, EventArgs e) {
    Master.TopMessage = "My top message";
  }
}

It looks like good code but it doesn't work. My TopMessage will never be shown. If you try to debug this code you'll see that when you instantiate TopMessage property in MyPage.Page_Load all is going well and value is successfully saved to _topMessage variable. But when it will be read from Main.Page_Load it is empty. Frankly, I don't know why. I have some guesses only. But it seems I found solution.

Solution

The trick is to use Context.Items collection.

//Main.master
//-------------
public partial class Main : System.Web.UI.MasterPage {
  
  public string TopMessage {
    get {
       if (Context.Items["_topMessage"] != null)
          return Context.Items["_topMessage"].ToString();
       else
          return string.Empty;
    }
    set {
        Context.Items["_topMessage"] = value;
    }
  }

  protected void Page_Load(object sender, EventArgs e) {
    TopMessageLiteral.Text = TopMessage;
  }
}

In this way TopMessage value will never be lost.

One More Solution

Suggested by Irwan Hassan technic need not Main.master <- Child.master inheritance

//MyPage.aspx 
//----------
public partial class MyPage: System.Web.UI.Page {

  protected void Page_Load(object sender, EventArgs e) {
    Master.Master.TopMessage = "My top message";
  }
}

History

May 09, 2007: just add a piece of code to play experiments

May 10, 2007: add one more solution

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Bobac

Web Developer

Ukraine

Member

Article Top

Poor

Excellent

Add a reason or comment to your vote: x
Votes of 3 or less require a comment

Comments and Discussions

You must Sign In to use this message board. (secure sign-in)

Search this forum
	Profile popups Noise Layout Per page

There's a built-in way to achieve this:

Jim Raley

7:03 9 Dec '08

Look in the sdk regarding "MasterType" and add this in the child master (not the code behind):

<%@ MasterType VirtualPath="~/ Main.Master" %>

You can also point this at a code file that can serve as a base class. In this latter case, you'd use "TypeName" instead of VirtualPath. You can't use both.

Then, in your child master, just say "this.Master.myTopProperty=whatever" and you're good to go.

Jim

A 5 from me!

Andrei Rinea

6:14 12 Oct '07

Thanks! This solved my problem! BTW: VS 2008 Beta 2 seems to be ok and handles nested master pages visually well Personal blog http://andreir.wordpress.com
Sign In·View Thread·Permalink

Try Master.Master.TopMessage = ...

Irwan Hassan

7:23 9 May '07

Hi, I'm new to asp.net but I'm doing programming in asp for few years. Recently I used nested master pages and it's not easy to get the main master page property. Please try this Master.Master.TopMessage = ... I hope the above solve your problem.
Sign In·View Thread·Permalink	4.40/5 (2 votes)

Re: Try Master.Master.TopMessage = ...

Bobac

2:54 10 May '07

It works!!! You are Master! Thanks! And in that case we have no use of inheritance It's a pity because with hierarchy, I think, it looks stronger.
Sign In·View Thread·Permalink

Re: Try Master.Master.TopMessage = ...

Irwan Hassan

3:51 10 May '07

I know this will work because I just recently developed a page with nested master page. I have few public property in the main master page need to be in the last child. So I use this technique. I'm happy, at least I share my experience with another programmer.
Sign In·View Thread·Permalink

Event firing sequence

Brian Lowe

22:05 7 May '07

But when it will be read from Main.Page_Load it is empty. Frankly, I don't know why. I have some guesses only.

I have a guess too: Check out the event sequencing for the classes.

Asp.NET collects together all of the objects that will make up your final page and fires child events before the equivalent parent event. So the Page_Load() event in the child object gets fired before the Page_Load() in its parent, etc.

If you need code in a master to make use of data initialized in a child, or vice versa, you must take care to use events in the right sequence. Each page has PreInit(), Init() and Load() events, and many others.

Unfortunately I have not been able to find a definitive list telling the absolute sequence of when each event gets fired, especially when considering nested classes or objects, but I have been able to find my own sequence by inserting Trace.Write() statements into lots of event code and then watch the sequence by setting Trace="true" in the page while debugging.

e.g.

class Main

{

  Page_PreInit() { Trace.Write("Main PreInit()"); }

  Page_Init() { Trace.Write("Main Init()"); }

  Page_Load() { Trace.Write("Main Load()"); }

}

 

class Child

{

  Page_PreInit() { Trace.Write("Child PreInit()"); }

  Page_Init() { Trace.Write("Child Init()"); }

  Page_Load() { Trace.Write("Child Load()"); }

}

This is commonly needed when you're using user controls in a page and you need to make sure the control data gets initialized. You would use the Page_Init() event of the main page to set up data values that are referenced by the user controls' Page_Load() because all their Page_Load() events get fired before the main Page_Load() event.

I hope this helps.

Brian
----@

Re: Event firing sequence

Bobac

13:19 8 May '07

Hi, Brian

First of all, Thank you for your reply.

I agree with you that problem described above related with "event sequence" I'd say "life cycle".
But.

1.

"So the Page_Load() event in the child object gets fired before the Page_Load() in its parent, etc."

Are you sure? Possibly you meant Page_Init().

2.
About Tracing: no question, it's a really good tool and debugging breakpoints too. Smile | :)

3.
"If you need code in a master …"
Yes I talked about nested master pages.
"This is commonly needed when you're using user controls"
And if you compare master pages and user controls you are quite right - theirs nature is similar.
According to K. Scott Allen, "In fact, the MasterPage class derives from the UserControl class. I've found it useful to only think of master pages as masters during design time. When the application is executing, it's better to think of the master page as just another child control."
Here is his full "ASP.Net 2.0 - Master Pages: Tips, Tricks, and Traps" article.

But if we are talking about not easy structure like (Page->UserControl or Masterpage->Page), and we are! In our case the situation will be little bit different.
Let's see.
Easy case (Page->UserControl and Masterpage->Page):
Events order:

1 UserControl_Init

2 Page_Init

3 Page_Load

4 UserControl_Load

and

1 Masterpage_Init

2 Page_Init

3 Page_Load

4 Masterpage_Load

Masterpage behaves like an usual UserControl.
Let's make it complicated. (Page->UserControl->NestedUserControl and MainMasterpage-> ChildMasterpage->Page)
Events order:

1 NestedUserControl_Init

2 UserControl_Init

3 Page_Init

4 Page_Load

5 UserControl_Load

6 NestedUserControl_Load

and

1 MainMasterpage_Init

2 ChildMasterpage_Init

3 Page_Init

4 Page_Load

5 ChildMasterpage_Load

6 MainMasterpage_Load

Do you see it? Events order aren't similar anymore.
Actually the reason of my note was not to find out "Why" but only share "How".
If you'd like to do some more experiments I attached test WebApplication. I think it would be interesting if we found "Why".

Regards,
Bobac

PS: you possibly saw it but for any case
ASP.NET Page Life Cycle Overview
ASP.NET Application Life Cycle Overview

Re: Event firing sequence

Brian Lowe

3:43 9 May '07

You obviously didn't need my clumsy attempt at help! Smile | :)

I did work through the 2 overview pages you mention, but each discusses only its own immediate effect, and as soon as I added in a user control or master page I got a different result, so I needed a better definitive guide.

Your rendition of the event ordering in the life cycle, and the notion that a master page behaves as if it were a user control when it comes to the ordering certainly helps my understanding.

Thanks!

Brian
----@