Basic Ajax Help

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MikeB - 11 Oct 2007 00:33 GMT

Hello All, I am new to ajax and wanted to start by trying something simple.
I have a web form with an updatepanel and then inside the update panel I
have a listbox. Then outside of the updatepanel I have a button. In my
buttons click event in the cs / code behind, I have a loop that just inserts
items in the listbox. My question is, once I click the button and the loop
begins, how do I get it to update the listbox? Does this make since?
Basically, this kind of mimics a update page I plan on doing next.

TIA

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IfThenElse - 11 Oct 2007 00:47 GMT

You don't have to do anything it updates by itself. hence the updatepanel.

> Hello All, I am new to ajax and wanted to start by trying something
> simple. I have a web form with an updatepanel and then inside the update
[quoted text clipped - 5 lines]
>
> TIA

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MikeB - 11 Oct 2007 01:22 GMT

That is what I though however, it is not updating. I must be missing
something. Here is my code behind:

protected void Button1_Click(object sender, EventArgs e)
{

Thread firstThread = new Thread(new ThreadStart(Coundown));
firstThread.Start();
}

public void Coundown()
{
for (int i = 0; i < 100; i++)
{

ListBox1.Items.Add(i.ToString());
Thread.Sleep(250);
}
}

Here is my aspx page:

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<div>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:ListBox ID="ListBox1" runat="server"
Width="498px"></asp:ListBox>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ListBox1"
EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click"
Text="Button" />
</form>

> You don't have to do anything it updates by itself. hence the updatepanel.
>
[quoted text clipped - 8 lines]
>>
>> TIA

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IfThenElse - 11 Oct 2007 01:35 GMT

This will not update until the end. the browser has to get something back.

> That is what I though however, it is not updating. I must be missing
> something. Here is my code behind:
[quoted text clipped - 48 lines]
>>>
>>> TIA

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MikeB - 11 Oct 2007 01:41 GMT

Using AJAX, am I able to update the listbox as it is updated?

> This will not update until the end. the browser has to get something
> back.
[quoted text clipped - 51 lines]
>>>>
>>>> TIA

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IfThenElse - 11 Oct 2007 01:57 GMT

Your thread does not end to send anything back??

> Using AJAX, am I able to update the listbox as it is updated?
>
[quoted text clipped - 53 lines]
>>>>>
>>>>> TIA

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bruce barker - 11 Oct 2007 03:30 GMT

you're missing the basic concept of browsers and ajax. ajax is a pattern
used in javascript to make a web service call (via xmlhttprequest), and
then process the reponse, usually with some dynamic html.

the updatepanel when triggered:

1. javascript sends a request to page with all form fields via
xmlhttprequest
2. the server processes the form data like a normal postback
3. the server runs a special render that only renders the updatepanel(s)
4. the server sends updatepanel html back the client
5. a javascript async event is fired by xmlhttprequest when the html is
returned
6. javascript event handler replaces the contents of the updatepanel
with the html

so nothing happens in the update anel until the html is sent back.

-- bruce (sqlwork.com)

> Using AJAX, am I able to update the listbox as it is updated?
>
[quoted text clipped - 53 lines]
>>>>>
>>>>> TIA

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Bjorn Sagbakken - 11 Oct 2007 20:37 GMT

What about adding this to the end of your code:

UpdatePanel1.update();

This will refresh the update panel from outside of the updatepanel to
reflect the changes in the list.

Bjorn

> Using AJAX, am I able to update the listbox as it is updated?
>
[quoted text clipped - 53 lines]
>>>>>
>>>>> TIA

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