Moving to ASP.NET

BrianWren · March 4th, 2005, 05:22 PM

I have a quandary.

I am working through Apressâ book Moving to ASP.NET: Web Development With VB .NET, and I have been taking SkillSoft online courses, reading the posts here (and answering some). After all of that, I got the idea that clicking a server control button submits the pageâs form, and resends the page to the browser.
Upon experimentation, I see that this is true.

When I click on a server control button, IEâs globe starts spinning, and it keeps spinning while the server-code is paused.
When I let the server proceed, the web page is sent to the browser all over again. Ie, the text-box has its original value all over again.

Apparently if you want to use server-side code for buttons and such, you need to take the state of the controls, and echo that back to the browser.
(It seems that this in turn will modify what each controlâs âdefaultValueâ is, but that's not a âshow-stopper.â)

I created:

Code:

<%@ Page Language="vb" AutoEventWireup="false" Codebehind="WebForm1.aspx.vb" Inherits="test_events.WebForm1"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
   <HEAD>
      <title>WebForm1</title>
      <meta name="GENERATOR" content="Microsoft Visual Studio .NET 7.1">
      <meta name="CODE_LANGUAGE" content="Visual Basic .NET 7.1">
      <meta name="vs_defaultClientScript" content="JavaScript">
      <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
   </HEAD>
   <body MS_POSITIONING="GridLayout" bgColor="#b9e9ff">
      <form id="Form1" method="post" runat="server">
         <asp:Button id="WbFrms_Sect_Btn" 
              style="Z-INDEX: 10; LEFT: 98px; POSITION: absolute; TOP: 50px"
              runat="server" Width="160px" Height="32px" 
              Text="From Web Forms Sect."></asp:Button>
         <INPUT id="Box1" 
             style="Z-INDEX: 20; LEFT: 98px; WIDTH: 160px; POSITION: absolute; TOP: 90px; HEIGHT: 24px"
             type="text" size="21" value="Box 1">
      </form>
   </body>
</HTML>

I put a breakpoint in Sub WbFrms_Sect_Btn_Click() to examine the environment, and ran it.

Sure enough, if I change the contents of the text box, when I click WbFrms_Sect_Btn the breakpoint is triggered (with IEâs globe spinning around). When I let the code finish, the textbox gets it original value put back into it.

So.

If I want to run a click event (or whatever) through the auspices of a server control, how do I maintain the values in the controls that the user has thus far modified?
BTW: I tried to examine the value in the textbox with Request.Form("Box1") to no avail. Thimble, thimble: Where is the thimble? (Where is that value?)

Also, If I donât want to use data binding for the value of a given control (letâs just say a textbox for simplicityâs sake), how do I dynamically set its value?

I am a skilled VB6 Webclass programmer, but Iâm having a little trouble with understanding how to accomplish things that I know can be done, in this new environment.

katsarosj · March 8th, 2005, 03:26 PM

Hi Brian,

It looks like you are using a standard input box for your textbox. The easiest way for you to manipulate the values within textboxes are to use ASP.Net's WebControls. Within those controls you will find a textbox. Drag one onto your form.

Then from the code behind you should be able to modify it's properties. Just a simple example:

TextBox1.Text = "BlahBlah"

assuming that the name of your textbox is "Textbox1". Hope this helps.

J

BrianWren · March 9th, 2005, 04:04 PM

It does help some.

After posting this Q I started to see that that was where the book was trying to steer people.

Almost everything I have is in VB6 WebClasses, which (of course) use standard HTML controls, filling in the values by changing the contents of a pre-defined tag at the time the page is requested.

Isnât there a way to duplicate this model of dynamically filling in the contents of a page being sent to the browser? (It sounds like maybe there is, as you say âThe easiest way . . . â is with webcontrols, holding out the possibility that there is a less easy way?)

katsarosj · March 10th, 2005, 01:12 AM

You could put what I showed you:

TextBox1.Text = "BlahBlah"

in the Page_Load event of your code behind. When your page loads, the text of "TextBox1" would be "BlahBlah". Is this what you are looking for, or am I missing the boat?

J

BrianWren · March 10th, 2005, 12:58 PM

Doesnât that only work with controls that are runat=server? (That makes them behave a little differently, and loads more data into the hidden control that animates that feature.)

What triggered this question is that, if you click a webcontrol button, you make a round trip to the server to run its _Click() event. Any textboxes that have had their value changed will now be reset to their initial value.
So I guess that under those circumstances you would read what values were submitted on this âtrip,â and put those values into the controls that are being returned. How do you get that value to return it to the browser?

katsarosj · March 10th, 2005, 04:41 PM

Those values will only be changed if you want them to be changed, otherwise the state of the controls will be maintained. I'll give a little more clarification. If you add code to the Page_Load event to set Textbox1's text to a certain value, then yes it will change back to that value every time you post back to the server.

If, however, you tell it to only set that value the first time posting to the server, it won't. You do that by using the IsPostBack method. Try this. Add another webcontrol textbox to your form and call it TextBox2. Then add this to your Page_Load event:

'----------------------------------------------
If Not IsPostBack Then
TextBox1.Text = "BlahBlah"
End If
'----------------------------------------------

In your button click event add this:

'----------------------------------------------
TextBox2.Text = "BlahBlah2"
'----------------------------------------------

The first time you load the page, you should see "BlahBlah" in TextBox1, Textbox2 should have nothing. Change the text of TextBox1 to "Test" and click the button. TextBox1 will maintain its state and keep "Test". TextBox2, however, will be set to "BlahBlah2".

If you have used VB6 for Windows applications development, you should love this because it acts more like a Windows application than a Web app. This is possible because ASP.Net puts a hidden field along with your code that helps it to maintain state. If you look at your source code after your run your page you should see something like:

<input type="hidden" name="__VIEWSTATE" value="dDwxMjI3OTM5ODYxOzs+IZ4GE/WtG/2E0qo/i81UJBoAzXo=" />

This is how it maintains the values on your form. And yes, that only works when the control has runat=server specified.

Does this clarify it better?

J

BrianWren · March 10th, 2005, 07:41 PM

Yes, that âIsPostBackâ is interesting. There is a lot of potential there.

But just for curiosityâs sake:

  1 If a control is not runat=server, then directly setting it on a 'roundtrip' is not supported?
  2 Are the non-runat=server controlsâ values available?
     Eg, isnât there a Request.Form collection when a webcontrolâs _Click() event is triggered?

katsarosj · March 10th, 2005, 10:38 PM

Take a look at this page:

http://www.dotnetbips.com/displayarticle.aspx?id=8

It gives examples of using both web controls and html controls, but yes runat=server attribute is set. Another site here:

http://www.15seconds.com/issue/030211.htm

gives an example of using the Request.Forms collection to post to alternate pages, but I think you will get the idea. I personally can't remember the last time that I used this in one of my pages (I think it was when I was still doing classic ASP). You may be able to get a better answer for this in the ASP.Net forum, but they will likely tell you the same thing - that is, to try and move away from this methodology. Cheers.

J