PostBack twice for a button click?

  • Thread starter Thread starter pedestrian via DotNetMonster.com
  • Start date Start date
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pedestrian via DotNetMonster.com

I have a simple VB ASP.NET 2.0 page with a Button and a Label.
The Label text is "0". For each click of the button (btnAdd), it should
increment the Label text by 1.

The code:

Protected Sub btnAdd_Click(...) Handles btnAdd.Click
Trace.Warn("Before add: " & lblCounter.Text)
lblCounter.Text = (Int32.Parse(lblCounter.Text) + 1).ToString
Trace.Warn("After add: " & lblCounter.Text)
End Sub

However, each time I click the button, the label always increase
by 2 instead of the expected 1. What's the problem area?

I tried to debug using Trace.
I get the following result from the trace:

Begin Raise PostBackEvent
Before add: 0
After add: 1
Before add: 1
After add: 2
End Raise PostBackEvent

Is this signifies PostBack event is being run twice per button click?
How to solve it?

Thanks for your assistance.
 
Hi can you post all code except for designer generated code?
There's no way that the method should be executing twice.
 
(Default.aspx)
<%@ Page Language="VB" AutoEventWireup="true" CodeFile="Default.aspx.vb"
Inherits="_Default" Trace="true"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID="btnAdd" Text="Add" OnClick="btnAdd_Click"
runat="server" />
<asp:Label ID="lblCounter" Text="0" runat="server" />
</div>
</form>
</body>
</html>

(Default.aspx.vb)
Partial Class _Default
Inherits System.Web.UI.Page

Protected Sub btnAdd_Click(ByVal sender As Object, ByVal e As System.
EventArgs) Handles btnAdd.Click
Trace.Warn("Before add: " & lblCounter.Text)
lblCounter.Text = (Int32.Parse(lblCounter.Text) + 1).ToString
Trace.Warn("After add: " & lblCounter.Text)
End Sub
End Class
 
Sounds like you might have an event handler in the designer file in
addition to the specification in the label tag.
 
pedestrian said:
(Default.aspx)
<%@ Page Language="VB" AutoEventWireup="true" CodeFile="Default.aspx.vb"
Inherits="_Default" Trace="true"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID="btnAdd" Text="Add" OnClick="btnAdd_Click"
runat="server" />
<asp:Label ID="lblCounter" Text="0" runat="server" />
</div>
</form>
</body>
</html>

(Default.aspx.vb)
Partial Class _Default
Inherits System.Web.UI.Page

Protected Sub btnAdd_Click(ByVal sender As Object, ByVal e As System.
EventArgs) Handles btnAdd.Click
Trace.Warn("Before add: " & lblCounter.Text)
lblCounter.Text = (Int32.Parse(lblCounter.Text) + 1).ToString
Trace.Warn("After add: " & lblCounter.Text)
End Sub
End Class
Click to expand...

AutoEventWireup="true" - Find all of the <control name>_<event name>
methods add attach them to the <control name>.<event name> event

Handles <control name>.<event name> - Attach this method to the
<control name>.<event name> event.

So your btnAdd_Click method is being attached to the btnAdd.Click event
twice, and is hence being called twice. My normal advice would be to
set AutoEventWireup to false.

Damien
 
Thanks for valuable answer, Damien.
(Default.aspx)
<%@ Page Language="VB" AutoEventWireup="true" CodeFile="Default.aspx.vb"
Click to expand...
[quoted text clipped - 31 lines]
Regards,
Pedestrian, Penang.
Click to expand...

AutoEventWireup="true" - Find all of the <control name>_<event name>
methods add attach them to the <control name>.<event name> event

Handles <control name>.<event name> - Attach this method to the
<control name>.<event name> event.

So your btnAdd_Click method is being attached to the btnAdd.Click event
twice, and is hence being called twice. My normal advice would be to
set AutoEventWireup to false.

Damien
Click to expand...

--
Regards,
Pedestrian, Penang.

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