Selective Display of information on a panel

JohnInPomeroy · March 19th, 2010, 06:58 PM

Hi Imar,

I'm really enjoying working through your book. I'm moving from .asp to asp.net and so far mostly doing ok working through your text and examples.

Right now, I'm trying to display or not display some links depending on which page is currently being browsed. In the MasterPage, I dropped a panel into the SideBar Div and put my text on the panel.

Then in the code behind for the MasterPage, I have

Code:

Partial Class MasterPage
    Inherits System.Web.UI.MasterPage

    Public DisplayPanel As Boolean

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If DisplayPanel Then
            Panel1.Visible = True
        Else
            Panel1.Visible = False
        End If
    End Sub
End Class

Then I try to set the logic up in the individual pages like this

Code:

Partial Class AboutUs
    Inherits System.Web.UI.Page

    Public DisplayPanel As Boolean

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        DisplayPanel = False

    End Sub
End Class

I thought I could change the DisplayPanel variable to True or False in each page's code behind page depending on whether or not I want the Panel and links on it to be visible.

Except, if the MasterPage.vb says "Public DisplayPanel As Boolean = True" then the pages ALWAYS show the panel, no matter what I set DisplayPanel to in the individual pages. And if I have "Public DisplayPanel As Boolean" or "Public DisplayPanel As Boolean = False" in the MasterPage.vb, then the panel NEVER shows up.

Have any hints for me?

Thanks,

John

Imar · March 20th, 2010, 06:14 AM

Hi John,

Take a look at this:

Code:

 
Partial Class AboutUs
    Inherits System.Web.UI.Page
  Public DisplayPanel As Boolean
  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    DisplayPanel = False
  End Sub
End Class

What do you think this code does? Override the DisplayPanel of the Master Page? In that case; nope it doesn't. It simply creates *another* boolean inside the Content Page that in no way is associated with the one in the Master Page. If you want a property or field on a Master Page that you can control from a content page, you need to tell the content page the type of the Master Page so you can access its members. Try something like this:

1. Use the same Master Page as you have now with the public DisplayPanel field in it.

2. Create a content page based on this Master Page and add the following MasterType reference to it:

Code:

 
<%@ Page Title="" Language="VB" MasterPageFile="~/MasterPage.master" 
       AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>
<%@ MasterType VirtualPath="~/MasterPage.master" %>

Make sure you adjust the MasterPageFile and VirtualPath properties to point to your Master Page.

3. The Master property of your content page is now strongly typed to your specific Master Page, enabling you to do something like this in the Content Page:

Code:

 
Me.Master.DisplayPanel = False ' Or True

This should do the trick and hide or show the panel based on the value you pass to Me.Master.DisplayPanel.

A few other observations: Instead of a field, you can also use a property or even a ViewState property as explained in the bok. And you can collapse the If statement to this if you want:

Panel1.Visible = DisplayPanel

although you may find your expanded version easier to read.

Hope this helps,

Imar

JohnInPomeroy · March 20th, 2010, 10:58 AM

Thanks Imar,

To answer your first question, yes. I thought that by declaring the variable public in the Master Page and then in the page based on the Master Page declaring the "same" variable public again that what I wanted to do would work. Guess I need to do more reading and coding/playing around.

Thanks for your suggestions. I'm off to have a cup of coffee and implement them.

John

Imar · March 20th, 2010, 11:19 AM

Hi John,

Although at runtime the content of the master page is merged with that of the content page, the two are actually two separate classes, and their class definition is not merged.

It's like "merging" a zebra and a tiger. You may end up with a zoo. But if you added a NumberOfStripes property to the Zebra class, it doesn't end up as a property on the Tiger class ;-)

Cheers,

Imar

JohnInPomeroy · March 20th, 2010, 12:52 PM

Imar,

And it also works better when all the parts match. I followed your steps and it sort of worked. Some pages showed or didn't show the panel as planned, other pages showed it when they shouldn't....

Then I saw that in the top properties line of AboutMe.aspx, (and several other pages), where it should have been

Code:

<%@ Page Title="" Language="VB" MasterPageFile="~/MasterPages/MasterPage.master" AutoEventWireup="false" CodeFile="AboutMe.aspx.vb" Inherits="_Default" %>

the CodeFile= said CodeFile="BookInfo.aspx.vb"

I don't know how or when it was changed, I've been creating new pages by right-clicking on the project name in the explorer window not by copying and pasting files, but even I can finally figure out that it wouldn't matter how much code I changed in BookInfo.aspx.vb if the reference was to AboutMe.aspx.me.

Thank you again.

John

Imar · March 21st, 2010, 05:07 AM

Hi John,

The only time I see this happening is indeed when copying files or when renaming them outside of Visual Studio.

Oh well, it's working now..... ;-)

Imar