ASP .NET Maintaining the ViewState

in your Web Form.

Maintaining//维持 the ViewState//?

When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with a lot of information and the server comes back with an error. You will have to go back to the form and correct the information. You click the back button, and what happens.......ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your ViewState.

When a form is submitted in ASP .NET, the form reappears in the browser window together with all form values. How come? This is because ASP .NET maintains your ViewState. The ViewState indicates//是指 the status of the page when submitted to the server. The status is defined through a hidden field placed on each page//放在每一页中的隐藏的区域 with a <form runat="server"> control. The source could look something like this:

<form name="_ctl0" method="post" action="page.aspx" id="_ctl0">
            <input type="hidden" name="__VIEWSTATE"
            value="dDwtNTI0ODU5MDE1Ozs+ZBCF2ryjMpeVgUrY2eTj79HNl4Q=" />

.....some code

</form>

Maintaining the ViewState is the default setting//默认设置 for ASP.NET Web Forms. If you want to NOT maintain the ViewState, include the directive <%@ Page EnableViewState="false" %> at the top of an .aspx page or add the attribute//属性 EnableViewState="false" to any control//控件.

Look at the following .aspx file. It demonstrates//示范,演示 the "old" way to do it. When you click on the submit button, the form value will disappear:

<html>
            <body>

       <form action="demo_classicasp.aspx" method="post">
            Your name: <input type="text" name="fname" size="20">
            <input type="submit" value="Submit">
            </form>
            <%
            dim fname
            fname=Request.Form("fname")
            If fname<>"" Then
            Response.Write("Hello " & fname & "!")
            End If
            %>

      </body>
            </html>

Example

ASPX Source:

<html>
<body>

<form action="demo_classicasp.aspx" method="post">
Your name: <input type="text" name="fname" size="20">
<input type="submit" value="Submit">
</form>
<%
dim fname
fname=Request.Form("fname")
If fname<>"" Then
Response.Write("Hello " & fname & "!")
End If
%>

</body>
</html>

Output Result:

Your name:

if you input one persont'name:like:'shaohai',and then click the button"submit"

the output result:

Hello shaohai!

Here is the new ASP .NET way. When you click on the submit button, the form value will NOT disappear:

<script runat="server">
            Sub submit(sender As Object, e As EventArgs)
            lbl1.Text="Hello " & txt1.Text & "!"
            End Sub
            </script>

<html>
            <body>

            <form runat="server">
            Your name: <asp:TextBox id="txt1" runat="server" />
            <asp:Button OnClick="submit" Text="Submit" runat="server" />
            <p><asp:Label id="lbl1" runat="server" /></p>
            </form>

</body>
            </html>

Example

ASPX Source:

Output Result:

Your name:

if you input one persont'name:like:'shaohai',and then click the button"submit"

the output result:

Your name:
Hello shaohai!

posted on 2007-01-16 11:21 改变热爱阅读(207) 评论(0) 收藏举报

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ASP .NET Maintaining the ViewState

Maintaining//维持 the ViewState//?

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