Professional ASP.NET 3.5 in C# and Visual Basic Part 30 pptx

Your GUID number from the master page is: Enter your name: C# protected void Page_LoadCompleteobject sender, EventArgs e { Label1.Text = Master.FindControl"Label1" as Label.

Trang 1

<b>Your GUID number from the master page is:<br />

<asp:Label ID="Label1" runat="server" /></b><p>

<b>Enter your name:</b><br />

<asp:Textbox ID="TextBox1" runat="server" />

<br />

<asp:Button ID="Button1" runat="server" Text="Submit"

OnClick="Button1_Click" /><br />

<br />

<asp:Label ID="Label2" runat="server" Font-Bold="True" />

</asp:Content>

<asp:Content ID="Content3" ContentPlaceHolderId="ContentPlaceHolder2"

runat="server">

<asp:Image ID="Image1" runat="server" ImageUrl="Wrox.gif" />

</asp:Content>

C#

<%@ Page Language="C#" MasterPageFile="~/wrox.master" %>

<script runat="server">

protected void Page_LoadComplete(object sender, EventArgs e)

{

Label1.Text = (Master.FindControl("Label1") as Label).Text;

}

protected void Button1_Click(object sender, EventArgs e)

{

Label2.Text = "<b>Hello " + TextBox1.Text + "!</b>";

}

</script>

In this example, the master page in Listing 5-8 first creates a GUID that it stores as a text value in a Label server control on the master page itself TheIDof this Label control isLabel1 The master page generates this GUID only on the first request for this particular content page From here, you then populate one of the content page’s controls with this value

The interesting thing about the content page is that you put code in thePage_LoadCompleteevent han-dler so that you can get at the GUID value that is on the master page This new event in ASP.NET fires immediately after thePage_Loadevent fires Event ordering is covered later, but thePage_Loadevent

in the content page always fires before thePage_Loadevent in the master page In order to get at the

newly created GUID (if it is created in the master page’sPage_Loadevent), you have to get the GUID in

an event that comes after thePage_Loadevent — and that is where thePage_LoadCompletecomes into play Therefore, within the content page’sPage_LoadCompleteevent, you populate a Label server control within the content page itself Note that the Label control in the content page has the sameIDas the Label control in the master page, but this doesn’t make a difference You can differentiate between them with the use of theMasterproperty

Not only can you get at the server controls that are in the master page in this way, you can get at any cus-tom properties that the master page might expose as well Look at the master page shown in Listing 5-10;

it uses a custom property for the<h1>section of the page

Trang 2

Listing 5-10: A master page that exposes a custom property

VB

<%@ Master Language="VB" %>

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

If Not Page.IsPostBack Then Label1.Text = Guid.NewGuid().ToString() End If

End Sub

Dim m_PageHeadingTitle As String = "My Company"

Public Property PageHeadingTitle() As String

Get Return m_PageHeadingTitle End Get

Set(ByVal Value As String) m_PageHeadingTitle = Value End Set

End Property

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >

<head id="Head1" runat="server">

<title>My Company Master Page</title>

<asp:ContentPlaceHolder id="head" runat="server">

</asp:ContentPlaceHolder>

</head>

<body>

<form id="Form1" runat="server">

<table cellpadding="3" border="1">

<tr bgcolor="silver">

<td colspan="2">

<h1><%= PageHeadingTitle %></h1>

<b>User’s GUID:  

<asp:Label ID="Label1" runat="server" /></b>

</td>

</tr>

<tr>

<td>

<asp:ContentPlaceHolder ID="ContentPlaceHolder1"

runat="server">

</td>

<td>

<asp:ContentPlaceHolder ID="ContentPlaceHolder2"

runat="server">

</td>

</tr>

<tr>

Trang 3

<td colspan="2">

</td>

</tr>

</table>

</form>

</body>

</html>

C#

<%@ Master Language="C#" %>

protected void Page_Load(object sender, EventArgs e)

{

if (!Page.IsPostBack)

{

Label1.Text = System.Guid.NewGuid().ToString();

}

string m_PageHeadingTitle = "My Company";

public string PageHeadingTitle

{

get

{

return m_PageHeadingTitle;

}

set

{

m_PageHeadingTitle = value;

}

</script>

In this master page example, the master page is exposing the property you created called

PageHead-ingTitle A default value of"My Company"is assigned to this property You then place it within the

HTML of the master page file between some<h1>elements This makes the default value become the

heading used on the page within the master page template Although the master page already has a

value it uses for the heading, any content page that is using this master page can override the<h3>title heading The process is shown in Listing 5-11

Listing 5-11: A content page that overrides the property from the master page

VB

<%@ Page Language="VB" MasterPageFile="~/Wrox.master" %>

<%@ MasterType VirtualPath="~/Wrox.master" %>

Continued

Trang 4

Master.PageHeadingTitle = "My Company-Division X"

End Sub

</script>

C#

<%@ Page Language="C#" MasterPageFile="~/Wrox.master" %>

{

Master.PageHeadingTitle = "My Company-Division X";

}

</script>

From the content page, you can assign a value to the property that is exposed from the master page by

the use of theMasterproperty As you can see, this is quite simple to do Remember that not only can you

get at any public properties that the master page might expose, but you can also retrieve any methods

that the master page contains as well

The item that makes this all possible is the use of theMasterTypepage directive TheMasterType

direc-tive allows you to make a strongly typed reference to the master page and allows you to access the master

page’s properties via theMasterobject

Earlier, we showed you how to get at the server controls that are on the master page by using the

Find-Control()method TheFindControl()method works fine, but it is a late-bound approach, and as such,

the method call may fail if the control was removed from markup Use defensive coding practices and

always check for null when returning objects fromFindControl() Using the mechanics just illustrated

(with the use of public properties shown in Listing 5-10), you can use another approach to expose any

server controls on the master page You may find this approach to be more effective

To do this, you simply expose the server control as a public property, as shown in Listing 5-12

Listing 5-12: Exposing a server control from a master page as a public property

VB

Public Property MasterPageLabel1() As Label

Get Return Label1 End Get

Set(ByVal Value As Label) Label1 = Value End Set

End Property

</script>

Trang 5

<%@ Master Language="C#" %>

public Label MasterPageLabel1

{

get

{

return Label1;

}

set

{

Label1 = value;

}

</script>

In this case, a public property calledMasterPageLabel1provides access to the Label control that uses

theIDofLabel1 You can now create an instance of theMasterPageLabel1property on the content page and override any of the attributes of the Label server control So if you want to increase the size of the

GUID that the master page creates and displays in theLabel1server control, you can simply override

theFont.Sizeattribute of the Label control, as shown in Listing 5-13

Listing 5-13: Overriding an attribute from the Label control that is on the master page

VB

<%@ Page Language="VB" MasterPageFile="~/Wrox.master" %>

Master.MasterPageLabel1.Font.Size = 25

End Sub

</script>

C#

<%@ Page Language="C#" MasterPageFile="~/Wrox.master" %>

{

Master.MasterPageLabel1.Font.Size = 25;

}

</script>

This approach may be the most effective way to get at any server controls that the master page exposes

to the content pages

Trang 6

Specifying Default Content

in the Master Page

As you have seen, the master page enables you to specify content areas that the content page can use

Master pages can consist of just one content area, or they can be made up of multiple content areas The

nice thing about content areas is that when you create a master page, you can specify default content for

the content area This default content can then be left in place and utilized by the content page if you

choose not to override it Listing 5-14 shows a master page that specifies some default content within a

content area

Listing 5-14: Specifying default content in the master page

<head runat="server">

<title>My Company</title>

</head>

<body>

<form id="form1" runat="server">

<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">

Here is some default content

</asp:ContentPlaceHolder><p>

Here is some more default content

</asp:ContentPlaceHolder></p>

</form>

</body>

</html>

To place default content within one of the content areas of the master page, you simply put it in the

ContentPlaceHolderserver control on the master page itself Any content page that inherits this master

page also inherits the default content Listing 5-15 shows a content page that overrides just one of the

content areas from this master page

Listing 5-15: Overriding some default content in the content page

<%@ Page Language="VB" MasterPageFile="~/MasterPage.master" %>

<asp:Content ID="Content3" ContentPlaceHolderId="ContentPlaceHolder2"

runat="server">

Here is some new content

</asp:Content>

This code creates a page with one content area that shows content coming from the master page itself, in

addition to other content that comes from the content page (see Figure 5-10)

The other interesting point when you work with content areas in the design mode of Visual Studio 2008

is that the smart tag allows you to work easily with the default content

Trang 7

Figure 5-10

When you first start working with the content page, you will notice that all the default content is at first populated in all the Content server controls You can change the content by clicking on the control’s

smart tag and selecting the Create Custom Content option from the provided menu This option enables you to override the master page content and insert your own defined content After you have placed

some custom content inside the content area, the smart tag shows a different option — Default to

Mas-ter’s Content This option enables you to return the default content that the master page exposes to the

content area and to erase whatever content you have already placed in the content area — thereby sim-ply returning to the default content If you choose this option, you will be warned that you are about to delete any custom content you placed within the Content server control (see Figure 5-11)

Figure 5-11

After changing one of the Content control’s default content, you might be presented with something like Figure 5-12

Programmatically Assigning the Master Page

From any content page, you can easily assign a master page programmatically You assign the

mas-ter page to the content page using thePage.MasterPageFileproperty This can be used regardless of

whether another master page is already assigned in the@Pagedirective

To accomplish this, you use this property through thePreInitevent ThePreInitevent is the earliest

point in which you can access the Page lifecycle For this reason, this is where you need to assign any

master page that is used by any content pages ThePreInitis an important event to make note of when you are working with master pages, as this is the only point where you can affect both the master and

content page before they are combined into a single instance Listing 5-16 illustrates how to assign the

master page programmatically from the content page

Trang 8

Figure 5-12

Listing 5-16: Using Page_PreInit to assign the master page programmatically

VB

<%@ Page Language="VB" %>

Protected Sub Page_PreInit(ByVal sender As Object, ByVal e As System.EventArgs)

Page.MasterPageFile = "~/MyMasterPage.master"

End Sub

</script>

C#

<%@ Page Language="C#" %>

protected void Page_PreInit(object sender, EventArgs e)

{

Page.MasterPageFile = "~/MyMasterPage.master";

}

</script>

Trang 9

In this case, when the page is dynamically being generated, the master page is assigned to the content

page in the beginning of the page construction process It is important to note that the content page must have the expected Content controls; otherwise an error is thrown

Nesting Master Pages

I hope you see the power that master pages provide to help you create templated Web applications So far, you have been creating a single master page that the content page can use Most companies and

organizations, however, are not just two layers Many divisions and groups exist within the organization that might want to use variations of the master by, in effect, having a master page within a master page With ASP.NET, this is quite possible

For example, imagine that Reuters is creating a master page to be used throughout the entire company

intranet Not only does the Reuters enterprise want to implement this master page company-wide, but

various divisions within Reuters also want to provide templates for the subsections of the intranet

directly under their control Reuters Europe and Reuters America, for example, each wants its own

unique master page, as illustrated in Figure 5-13

Figure 5-13

To do this, the creators of the Reuters Europe and Reuters America master pages simply create a master page that inherits from the global master page, as illustrated in Listing 5-17

Listing 5-17: The main master page

ReutersMain.master

<head runat="server">

<title>Reuters</title>

Continued

Trang 10

</head>

<body>

<form id="form1" runat="server">

<p><asp:Label ID="Label1" runat="server" BackColor="LightGray"

BorderColor="Black" BorderWidth="1px" BorderStyle="Solid"

Font-Size="XX-Large"> Reuters Main Master Page </asp:Label></p>

</form>

</body>

</html>

This is a simple master page, but excellent for showing you how this nesting capability works The main

master page is the master page used globally in the company It has the ContentPlaceHolder server

control with theIDofContentPlaceHolder1

When you create a submaster or nested master page, you accomplish this task in the same manner as

you would when building any other master page From the Add New Item dialog, select the Master Page

option and make sure you have the Select master page option selected, as illustrated in Figure 5-14 This

will take you again to the dialog that will allow you to make a master page selection

Figure 5-14

Định dạng
Số trang	10
Dung lượng	333,25 KB