tags:

views:

79

answers:

4
+1  Q: 

Problem with very simple ASP.NET 3.5 app, using C#

My problem is that I can only seem to click the button once, if I click multiple times it's like it's dead. Doesn't do anything. So if I click it once it sets the text to "Works". How come it doesn't keep alternating between values when I click many times?

I have the following C# code (I know I am using too many namespaces, but please disregard that); 

using System;
using System.Collections.Generic;
using System.Data;
using System.Web.Security;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
{
    Label1.Text = "Click to test";
}

protected void Click(object sender, EventArgs e)
{

    if (Label1.Text == "Works")
    {
        Label1.Text = "Try again";
    }

    else
    {
        Label1.Text = "Works";
    }
}
}

And here is the ASPX code;

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;

<html xmlns="http://www.w3.org/1999/xhtml"&gt;
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />
        </Triggers>
    </asp:UpdatePanel>
    <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Click" /> 

    </form>
</body>
</html>
+6  A: 

In your Page_Load you need to check IsPostBack If it is a postback you shouldn't set the control value.

protected void Page_Load(object sender, EventArgs e)
{ 
     if (!IsPostBack)
        Label1.Text = "Click to test";
}

Or in the case of an ajax update, it's IsAutoPostback (I think!)

Sophie88  2010-03-02 15:22:58
For ajax update, it's Page.IsCallBack.
madatanic  2010-03-02 15:26:03
Ahh, that helped. It works perfectly with "!IsPostBack", but I was trying to make it an async update. What am I missing to do that? I don't want a postback, I just want the updatepanel (which only contains the label) to be updated. Any suggestion?
cc0  2010-03-02 15:41:59
@cc0: I think that your trigger needs to go before your ContentTemplate code.
Ardman  2010-03-02 15:48:58
@Ardman: Good suggestion, I tried it. And I tried using "!Page.IsCallBack", to no avail. Any other suggestion?
cc0  2010-03-02 15:53:51
@cc0: the other suggestion is to remove the EventName from the AsyncPostBackTrigger
Ardman  2010-03-02 15:58:04
@Ardman: Tried that too, same result :( Any other tip?
cc0  2010-03-02 16:02:05
@cc0: I have literally just created a new project and copied your code into it (except for the ASPX headings) and added Sophie88's suggestion and it works. May I suggest that you try and do the same?
Ardman  2010-03-02 16:09:44
@Ardman: I did, and it does work if I use the !IsPostBack, but that is not an asynchronous update, right? That updates the whole page.
cc0  2010-03-02 16:15:06
Would I need something like this in my C# code?protected void Page_Load(object sender, EventArgs e) { ScriptManager1.RegisterAsyncPostBackControl(Button1); }
cc0  2010-03-02 16:20:58
@cc0: You are correct in the fact that it posts back the whole page.
Ardman  2010-03-02 16:23:34
Hmm, then all the ajax stuff is wasted. Is there no way I can fix this to be a partial postback?
cc0  2010-03-02 16:31:23
You're still getting partial rendering. Using IsPostBack is appropriate, even with an UpdatePanel. If you *just* want to test for async postbacks, try this: http://stackoverflow.com/questions/265686/how-can-you-tell-if-a-method-is-being-run-in-updatepanel-postback
Greg  2010-03-02 17:04:22
Thanks so much! Solved :]
cc0  2010-03-02 17:14:52
+1  A: 

Each time you load the page you are setting the Label1.Text to "Click to test" (Page_Load happens every time the page is displayed), then the click event is triggered and correctly sees that the label isn't set to "Works" and so sets it to "Works".

How to fix it, see Sophie88's answer.

Lazarus  2010-03-02 15:24:16
+2  A: 

Why are you setting the Label1.Text in the page_load?

IN your markup, just set the Text property to "Click to test"

  <asp:Label ID="Label1" runat="server" Text="Click to test"></asp:Label>
Jack Marchetti  2010-03-02 15:27:40
Good point, just to make a test.
cc0  2010-03-02 15:42:14
+5  A: 

The solution is what Sophie88 suggested, but I wanted to add some additional detail to explain exactly what's happening.

User initially requests page: (IsPostBack is false )

  1. Aspx markup is parsed: Label1.Text is "Label"
  2. Page_Load fires, sets Label1.Text to "Click to test"

User clicks button the first time: (IsPostBack is true)

  1. Aspx markup is parsed: Label1.Text is "Label"
  2. ViewState is restored, Label1.Text becomes "Click to test"
  3. Page_Load runs, sets Label1.Text to "Click to test"
  4. Click method runs. Label1.Text == "Click to test", so Label1.Text set to "Works"

User clicks button second time: (IsPostBack is true)

  1. Aspx markup is parsed: Label1.Text is "Label"
  2. ViewState is restored, Label1.Text becomes "Works"
  3. Page_Load runs, sets Label1.Text to "Click to test"
  4. Click method runs. Label1.Text == "Click to test", so Label1.Text set to "Works"
Greg  2010-03-02 15:49:15
Great explanation, thank you :]
cc0  2010-03-02 15:51:29
+1 - Nice explanation of the page life cycle.
DaveB  2010-03-02 16:33:20

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