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2010-07-29
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To read this article in its entirety, please visit asp.net: ASP.NET 4 and Visual Studio 2010 Web Development Overview
Web Forms
Web Forms has been a core feature in ASP.NET since the release of ASP.NET 1.0. Many enhancements have been in this area for ASP.NET 4, including the following:
- The ability to set meta tags.
- More control over view state.
- Easier ways to work with browser capabilities.
- Support for using ASP.NET routing with Web Forms.
- More control over generated IDs.
- The ability to persist selected rows in data controls.
- More control over rendered HTML in the FormView and ListView controls.
- Filtering support for data source controls.
Setting Meta Tags with the Page.MetaKeywords and Page.MetaDescription Properties
ASP.NET 4 adds two properties to the Page class, MetaKeywords and MetaDescription. These two properties represent corresponding meta tags in your page, as shown in the following example:
<head id="Head1" runat="server">
<title>Untitled Page</title>
<meta name="keywords" content="These, are, my, keywords" />
<meta name="description" content="This is the description of my page" />
</head>
These two properties work the same way that the page’s Title property does. They follow these rules:
- If there are no meta tags in the head element that match the property names (that is, name="keywords" for Page.MetaKeywords and name="description" for Page.MetaDescription, meaning that these properties have not been set), the meta tags will be added to the page when it is rendered.
- If there are already meta tags with these names, these properties act as get and set methods for the contents of the existing tags.
You can set these properties at run time, which lets you get the content from a database or other source, and which lets you set the tags dynamically to describe what a particular page is for.
You can also set the Keywords and Description properties in the @ Page directive at the top of the Web Forms page markup, as in the following example:
<%@ Page Language="C#" AutoEventWireup="true"
CodeFile="Default.aspx.cs"
Inherits="_Default"
Keywords="These, are, my, keywords"
Description="This is a description" %>
This will override the meta tag contents (if any) already declared in the page.
The contents of the description meta tag are used for improving search listing previews in Google. (For details, see Improve snippets with a meta description makeover on the Google Webmaster Central blog.) Google and Windows Live Search do not use the contents of the keywords for anything, but other search engines might. For more information, see Meta Keywords Advice on the Search Engine Guide Web site.
These new properties are a simple feature, but they save you from the requirement to add these manually or from writing your own code to create the meta tags.
Enabling View State for Individual Controls
By default, view state is enabled for the page, with the result that each control on the page potentially stores view state even if it is not required for the application. View state data is included in the markup that a page generates and increases the amount of time it takes to send a page to the client and post it back. Storing more view state than is necessary can cause significant performance degradation. In earlier versions of ASP.NET, developers could disable view state for individual controls in order to reduce page size, but had to do so explicitly for individual controls. In ASP.NET 4, Web server controls include a ViewStateMode property that lets you disable view state by default and then enable it only for the controls that require it in the page.
The ViewStateMode property takes an enumeration that has three values: Enabled, Disabled, and Inherit. Enabled enables view state for that control and for any child controls that are set to Inherit or that have nothing set. Disabled disables view state, and Inherit specifies that the control uses the ViewStateMode setting from the parent control.
The following example shows how the ViewStateMode property works. The markup and code for the controls in the following page includes values for the ViewStateMode property:
<form id="form1" runat="server">
<script runat="server">
protected override void OnLoad(EventArgs e) {
if (!IsPostBack) {
label1.Text = label2.Text = "[DynamicValue]";
}
base.OnLoad(e);
}
</script>
<asp:PlaceHolder ID="PlaceHolder1" runat="server" ViewStateMode="Disabled">
Disabled: <asp:Label ID="label1" runat="server" Text="[DeclaredValue]" /><br />
<asp:PlaceHolder ID="PlaceHolder2" runat="server" ViewStateMode="Enabled">
Enabled: <asp:Label ID="label2" runat="server" Text="[DeclaredValue]" />
</asp:PlaceHolder>
</asp:PlaceHolder>
<hr />
<asp:button ID="Button1" runat="server" Text="Postback" />
<%-- Further markup here --%>
As you can see, the code disables view state for the PlaceHolder1 control. The child label1 control inherits this property value (Inherit is the default value for ViewStateMode for controls.) and therefore saves no view state. In the PlaceHolder2 control, ViewStateMode is set to Enabled, so label2 inherits this property and saves view state. When the page is first loaded, the Text property of both Label controls is set to the string "[DynamicValue]".
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