ASP.NET - Server Controls

Server controls are tags that are understood by the server.

Limitations//局限性 in Classic ASP

The listing below was copied from the previous chapter:

            <html>
            <body bgcolor="yellow">
            <center>
            <h2>Hello W3Schools!</h2>
            <p><%Response.Write(now())%></p>
            </center>
            </body>
            </html>

The code above illustrates//举例说明 a limitation in Classic ASP: The code block has to be placed where you want the output to appear.

With Classic ASP it is impossible//不可能的 to separate executable code from the HTML itself. This makes the page difficult to read, and difficult to maintain//维护,保养.

ASP.NET - Server Controls

ASP.NET has solved the "spaghetti//意大利式面条-code"//混淆在一起的 problem described above with server controls.

Server controls are tags//标签 that are understood by the server.

There are three kinds of server controls:

         1.HTML Server Controls - Traditional HTML tags

         2.Web Server Controls - New ASP.NET tags

         3.Validation//确认 Server Controls - For input validation //输入确认

1.ASP.NET - HTML Server Controls

HTML server controls are HTML tags understood by the server.

HTML elements in ASP.NET files are, by default, treated as text. To make these elements programmable, add a runat="server" attribute//属性 to the HTML element. This attribute//属性 indicates//指明 that the element should be treated as a server control. The id attribute//ID属性 is added to identify//区别 the server control// 服务器端控件.The id reference//参考id can be used to manipulate//操作 the server control at run time.

Note//注意: All HTML server controls must be within a <form> tag with the runat="server" attribute//属性. The runat="server" attribute indicates//指明 that the form should be processed//执行 on the server. It also indicates//指示 that the enclosed//那些被赋上的 controls can be accessed//访问 by server scripts.

In the following example we declare an HtmlAnchor//锚点 server control in an .aspx file. Then we manipulate//操作 the Href attribute//"href属性" of the HtmlAnchor control in an event handler//事件处理器 (an event handler is a subroutine//子程序 that executes code for a given//给定的 event). The Page_Load event//载入页面事件 is one of many events that ASP.NET understands:

         <script runat="server">
            Sub Page_Load
            link1.Href="http://www.w3schools.com"
            End Sub
            </script>
        <html>
            <body>
            <form runat="server">
            <a id="link1" runat="server">Visit W3Schools!</a>
            </form>
           </body>
            </html>

The executable code //可执行代码itself has been moved outside the HTML.

2.ASP.NET - Web Server Controls

Web server controls are special ASP.NET tags understood by the server.

Like HTML server controls, Web server controls are also created on the server and they require a runat="server" attribute//属性 to work. However, Web server controls do not necessarily map//映射 to any existing HTML elements and they may represent//代表 more complex elements.

The syntax//语法 for creating a Web server control//控件 is:

<asp:control_name id="some_id" runat="server" />

In the following example we declare a Button server control in an .aspx file. Then we create an event handler//事件处理器 for the Click event which changes the text on the button:

         <script runat="server">
            Sub submit(Source As Object, e As EventArgs)
            button1.Text="You clicked me!"
            End Sub
            </script>
       <html>
            <body>
            <form runat="server">
            <asp:Button id="button1" Text="Click me!"
            runat="server" OnClick="submit"/>
            </form>
         </body>
            </html>

3.ASP.NET - Validation//确定 Server Controls

Validation server controls is used to validate//确定 user-input. If the user-input does not pass validation//确定, it will display an error message to the user.

Each validation//确定 control performs//扮演,担当 a specific type of validation (like validating against a specific value or a range of values).

By default, page validation is performed when a Button, ImageButton, or LinkButton control is clicked. You can prevent//预防,阴止 validation when a button control is clicked by setting the CausesValidation property//性质 to false.

The syntax//语法 for creating a Validation server control is:

<asp:control_name id="some_id" runat="server" />

In the following example we declare one TextBox control, one Button control, and one RangeValidator control in an .aspx file. If validation fails, the text "The value must be from 1 to 100!" will be displayed in the RangeValidator control:

         <html>
            <body>
            <form runat="server">
            Enter a number from 1 to 100:
            <asp:TextBox id="tbox1" runat="server" />
            <br /><br />
            <asp:Button Text="Submit" runat="server" />
            <br />
            <asp:RangeValidator
            ControlToValidate="tbox1"
            MinimumValue="1"
            MaximumValue="100"
            Type="Integer"
            EnableClientScript="false"
            Text="The value must be from 1 to 100!"
            runat="server" />
            </form>
            </body>
            </html>

posted on 2007-01-15 16:09  改变热爱  阅读(206)  评论(0)    收藏  举报

导航