May 072006
 

突然想到一个问题,既然asp.net提供了WebControl,功能又那么强大,接口又那么统一,为什么还要用HTMLControl呢?
Google上找了一下,中文结果几乎完全统一:http://www.google.com/search?hl=zh-CN&inlang=zh-CN&newwindow=1&q=htmlcontrol+webcontrol&lr=lang_zh-CN%7Clang_zh-TW

[quote]Web控件和Html控件虽然好多功能相同并且长得很像

但是它们的内部实现机制是完全不一样的

Web控件要比Html控件执行效率要好

1. 使用起来也相当方便,举个简单的例子,例如Button的生成:

Html控件是将庞大控件集合全部弄到页面中,用到哪个功能,就设置一下属性,如下:

这样会占用相当大的控件资源

Web控件是将集成式的拆解成单功能的:

这样就可以节省不必要的控件所占用的资源了

2.Web控件具有回送功能,能够用ViewState维持控件的状态.

Html控件则不能,当点击页面的操作,其状态就会丢失.

可以做这样的一个实验:

I. 分别建立两个文件: a.html b.aspx

II.在a.html页面中加Html控件的RadioButton和一个button,在b.aspx中加Web控件的adioButton和一个button

III.a.html直接双击浏览器运行,b.aspx通过IIS运行

IV.在a.html运行界面中,选中RadioButton,再单击Button按钮,会发现RadioButton会取消选中(丢失其状态),但在b.aspx页面执行同样的操作,RadioButton不会丢失,因为ViewState给它保存了状态. 您可以在运行界面点击浏览器菜单”查看”->“源文件”,打开Html代码文件,找到加密后的ViewState,类似于下面:

其实ViewState实现原理也是将一些信息放到隐藏的一个控件中,并且asp.net生成的ViewState信息
是存储在客户端的

这里要注意的一点是:

只有当格式为*.aspx文件,并且控件具有属性:”runat=server”时,回送功能才能打开

3. Html控件与Web控件最大的区别是它们对事件处理的方法不同。对于Html窗体控件,当引发一个事件时,浏览器会处理它。但对于Web控件,事件仅由浏览器生成,但浏览器不会处理它,客户端要给服务器发个信息,告诉服务器处理事件。 不过有些事件,比如:

按下键/移动/鼠标等事件,Asp.net中没有这些事件(因为这些事件即时性强,服务器处理得不够及时),这时候Html控件就发挥其作用了,结合Html事件

协助完成.
[/quote]

往后翻了n页,才找到一条比较详细的英文资料 http://www.codecomments.com/archive289-2005-9-607043.html

[quote]
This can be confusing to new ASP.Net developers. In fact, it is important to distinguish between several different types of ASP.Net Controls. Let me elaborate, if I may:

To begin with, let’s start with the parent NameSpace/Class for all ASP.Net Controls: System.Web.UI.Control. All ASP.Net Controls inherit this class.

Under this, there are about a dozen different classes and NameSpaces. I will only mention the most important ones here:

System.Web.UI.HtmlControls.HtmlControl

This is the base class from which all HtmlControls are derived. An HtmlControl is, at the very least, a simple, client-side HTML element, such as (Label),

(HtmlForm), or

(HtmlTable). There is no server-side aspect to any HtmlControl, unless you add a runat=”server” attribute to it. Adding this attribute gives you server-side control over the client-side HTML. You can create an HtmlControl from any client-side
HTML element. There are several ready-made HtmlControls, and an HtmlGenericControl which you can use for any other HTML element.

System.Web.UI.TemplateControl

This is the base Class for any ASP.Net Control that uses an HTML Template. There are 2 ready-made classes in the CLR that inherit this class.
System.Web.UI.Page, and System.Web.UI.UserControl. Generally, when people talk about “Web Controls,” they are talking about HtmlControls, WebControls, or the UserControl class, and not the Page class, although the Page class is, in fact a “Web Control” (Note the space in the term, which distinguishes “Web Control” from the class WebControl).

A UserControl is a Templated Control that is a container for pure HTML and other Web Controls. Of all the “Web Controls” that are used frequently in ASP.Net, the UserControl is the only one that has an HTML Template. It allows a block of HTML and server-side Controls to be treated as a single unit, or Control.

System.Web.UI.WebControls

This is a NameSpace, not a class. It has 6 different top-level classes:

System.Web.UI.WebControls.Literal

This class is used to encapsulate pure HTML in a container. It does nothing else. As ASP.Net is fully object-oriented, any HTML in a template that is not a server-side control is encapsulated in a Literal Control at run-time. It can also be used to pop any block of HTML into a Page or Control at run-time.

System.Web.UI.WebControls.PlaceHolder

This class is used, quite literally, as a “place holder.” It renders no HTML, but as a “Web Control,” (System.Web.UI.Conrol) it has a Controls Collection to which any other Control can be added. As it exists in a certain location in a Page or other Control, any Control can be popped into it at run-time. A UserControl could be used for this, by not having anything in it. But what would the purpose of the Template be? This class is not Templated, so it is easier to work with for this purpose.

System.Web.UI.WebControls.Repeater
System.Web.UI.WebControls.RepeaterItem

These 2 WebControls comprise a Repeater Control. The Repeater is a container for RepeaterItems. In addition, it has properties that allow for the addition of a number of System.Web.UI.ITemplate classes for fomatting the data contained in it. A Repeater is a sort of hybrid. While it is not a Templated Control, it is hosted in a Templated Control, and the Templates in it are placed in the Template of the hosting Templated Control. It is used for binding aggregate data (arrays, Collections, etc) to a block of repeating HTML in any format desired.

System.Web.UI.WebControls.WebControl

This is the base class for most of the Controls that are often confused with HtmlControls. A WebControl is a Control that ALWAYS has a server-side component, and WebControls all share the same fields, properties and methods of System.Web.UI.WebControl. In addition, each WebControl has fields, properties, and methods that correspond uniquely to the type of HTML element that the WebControl renders and interacts with at run-time.

HtmlControls are, therefore, by nature, leaner (consume less resources) than WebControls, but have less functionality as well.

System.Web.UI.WebControls.Xml

This class displays XML without any formatting or using XSLT. It is genreally used to display embedded XML in a web page.

In summary, the term “Web Control” is a fairly common, and confusing term that is generally used to encompass HtmlControls, WebControls, and the UserControl ASP.Net System.Web.UI.Control classes. It is important to distinguish between what type of “Web Control” is being discussed. The main differences between these 3 types of Controls are:

HtmlControls are lightweight Controls that can represent pure HTML, or add server-side functionality to client-side HTML.

WebControls are Controls that always have a server-side class associated with them, and provide a common server-side functionality for working with various HTML elements, and specific functionality for specific HTML elements.

A UserControl is a Templated Control which has a Template file, a container for both pure HTML and server-side class references in it, and allows for server-side manipulation of the server-side Controls in it. It allows a block of HTML and server-side Controls to be treated as a single unit, or Control.[/quote]

不知道谁说得更正确呢?

 Posted by at 4:36 pm

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