How to Use Master Pages (Conclusion) - How to access a public property of the master page from a content page
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Figure 3-9 shows how you can access a public property in a master page from a content page. As you can see in the top part of this figure, you use the MasterType directive in the aspx file of the content page to specify the name of the type used for the master page. The value you name in this directive specifies the type of the object returned by the content page’s Master property. So in this example, the Master property will return an object of type MasterPage. If you look at the class declaration in the previous figure, you’ll see that MasterPage is the name of the class that defines the master page.
The second part of this figure shows two procedures from the code-behind file for the Order.aspx content page. As you can see, the Page_Load procedure calls a procedure named DisplayCartMessage. This procedure determines the number of items currently in the shopping cart and sets the Text property of the label exposed by the master page’s MessageLabel property accordingly. But note that no value is assigned to the message label if the shopping cart is empty. In that case, the Page_Load procedure for the master page will set the label to the number of days remaining until Halloween.
Although using the MasterType directive in the content page’s aspx file makes it easier to access the properties of the master page, you should realize that this directive isn’t necessary. If you don’t specify the MasterType directive, the Master property will return an object of type Master. You can then cast this object to the actual type of your master page to access any properties you’ve created.
For example, you could use code like this to assign text to the MessageLabel property:
If Cart.Count = 1 Then
CType(Me.Master, MasterPage).MessageLabel.Text _
= "There is one item in your cart."
ElseIf Cart.Count > 1 Then
CType(Me.Master, MasterPage).MessageLabel.Text _
= "There are " & Cart.Count & " items in your cart."
End If
Here, the Master object is cast to MasterPage so its MessageLabel property can be accessed. The purpose of the MasterType directive is to avoid this awkward casting.
A portion of the Order.aspx page (figure 3-9)
<%@ Page Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="Order.aspx.vb" Inherits="Order" %>
<%@ MasterType TypeName="MasterPage" %>
<asp:Content ID="Content1" ContentPlaceHolderID="Main" Runat="server">
.
.
.
</asp:Content>
Two procedures from the code-behind file for the Order.aspx page
Protected Sub Page_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles Me.Load
If Not IsPostBack Then
ddlProducts.DataBind()
Me.DisplayCartMessage()
End If
SelectedProduct = GetSelectedProduct()
lblName.Text = SelectedProduct.Name
lblShortDescription.Text = _
SelectedProduct.ShortDescription
lblLongDescription.Text = _
SelectedProduct.LongDescription
lblUnitPrice.Text = FormatCurrency(SelectedProduct.UnitPrice)
imgProduct.ImageUrl = "Images\Products\" _
& SelectedProduct.ImageFile
End Sub
Private Sub DisplayCartMessage()
Dim Cart As SortedList = CType(Session("cart"), SortedList)
If Not Cart Is Nothing Then
If Cart.Count = 1 Then
Me.Master.MessageLabel.Text _
= "There is one item in your cart."
ElseIf Cart.Count > 1 Then
Me.Master.MessageLabel.Text _
= "There are " & Cart.Count & " items in your cart."
End If
End If
End Sub
Description
- The MasterType directive in an aspx file specifies the name of the master page type. If you include this directive in a content page, you can use the Master property in the code-behind file to access the exposed property of the master page.
Next: How to use nested master pages >>
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 This article is excerpted from chapter three of the book Murach’s ASP.NET 2.0 Upgrader’s Guide: VB Edition, written by Anne Boehm and Joel Murach (Murach, 2005; ISBN: 1-890774-36-7). Check it out today at your favorite bookstore. Buy this book now.
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