error in adding user controls at runtime

rushikesh.joshi · Mar 30, 2006

Hi All,

I have created my own WebControl and want to add it in my aspx page at
runtime.

it's compiling perfectly, but when i m going to execute, it gives me
error of "Object reference not set to an instance of an object." in my
server control (ascx.cs file)

There is a table in my user control with id "tdCell".

I'm creating a Label control at runtime in Page_Load of user control,
and want to add it in the "tdCell" by just tdCell.Controls.Add()....

There is a Panel on my aspx page with id "TBarPanel", and want to add
the user control at runtime. but i m getting error.

Any idea...I tried panel/placeholder/table every thing but it's not
working.
I also tried using LoadControl("MyControl.ascx"), but it's also not
working.

I put all code and error string for your reference.

Thanks & Regards,
Rushikesh

////////// MyControl.ascx /////////////

<%@ Control Language="C#" AutoEventWireup="true"
CodeFile="MyControl.ascx.cs" Inherits="MyControl" %>

<table cellpadding="0" cellspacing="0">
<tr>
<td id="tdCell" runat="server"></td>
</tr>
</table>

////////// MyControl.ascx.cs /////////////

using System;
using System.Data;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class MyControl: System.Web.UI.UserControl
{

protected void Page_Load(object sender, EventArgs e)
{
Label lbl = new Label();
lbl.Text = "Hello";
tdCell.Controls.Add(lbl);

}
}

//// //// MyControl_Test.aspx /////////

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

<%@ Register Src="MyControl.ascx" TagName="MyControl" TagPrefix="uc1"
%>

<!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

anel ID="TBarPanel" runat="server" Height="42px"
Width="100%">
</asp

anel>
</form>
</body>
</html>

//// //// MyControl_Test.aspx.cs /////////

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

public partial class TimeBarCtrl_Test : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
MyControl myctrl1 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl1);

MyControl myctrl2 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl2);

MyControl myctrl3 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl3);

}
}

////////////////////**********************Error

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not
set to an instance of an object.

Source Error:

Line 54: Label lbl = new Label();
Line 55: lbl.Text = "Hello";
Line 56: tdCell.Controls.Add(lbl);
Line 57:
Line 58:

Source File: d:\inetpub\wwwroot\MACT\Interface\TimeBarCtrl.ascx.cs
Line: 56

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an
object.]
TimeBarCtrl.Page_Load(Object sender, EventArgs e) in
d:\inetpub\wwwroot\MACT\Interface\TimeBarCtrl.ascx.cs:56
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object
o, Object t, EventArgs e) +13
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object
sender, EventArgs e) +45
System.Web.UI.Control.OnLoad(EventArgs e) +80
System.Web.UI.Control.LoadRecursive() +49
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
+3710

Karl Seguin [MVP] · Mar 30, 2006

More code would be helpful.

It should look something:

Control c = Page.LoadControl("controlFileName.ascx");
tdCell.Controls.Add(c);

From the brief description you've given, it looks like the error might
actually be happening in your contorl (you say the object reference is
occuring in an ascx file) so it's really hard to tell what exactly is going
on.

Karl

--
http://www.openmymind.net/
http://www.fuelindustries.com/

Hi All,

I have created my own WebControl and want to add it in my aspx page at
runtime.

it's compiling perfectly, but when i m going to execute, it gives me
error of "Object reference not set to an instance of an object." in my
server control (ascx.cs file)

There is a table in my user control with id "tdCell".

I'm creating a Label control at runtime in Page_Load of user control,
and want to add it in the "tdCell" by just tdCell.Controls.Add()....

There is a Panel on my aspx page with id "TBarPanel", and want to add
the user control at runtime. but i m getting error.

Any idea...I tried panel/placeholder/table every thing but it's not
working.
I also tried using LoadControl("MyControl.ascx"), but it's also not
working.

I put all code and error string for your reference.

Thanks & Regards,
Rushikesh

////////// MyControl.ascx /////////////

<%@ Control Language="C#" AutoEventWireup="true"
CodeFile="MyControl.ascx.cs" Inherits="MyControl" %>

<table cellpadding="0" cellspacing="0">
<tr>
<td id="tdCell" runat="server"></td>
</tr>
</table>

////////// MyControl.ascx.cs /////////////

using System;
using System.Data;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class MyControl: System.Web.UI.UserControl
{

protected void Page_Load(object sender, EventArgs e)
{
Label lbl = new Label();
lbl.Text = "Hello";
tdCell.Controls.Add(lbl);

}
}

//// //// MyControl_Test.aspx /////////

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

<%@ Register Src="MyControl.ascx" TagName="MyControl" TagPrefix="uc1"
%>

<!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>
<aspanel ID="TBarPanel" runat="server" Height="42px"
Width="100%">
</aspanel>
</form>
</body>
</html>

//// //// MyControl_Test.aspx.cs /////////

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

public partial class TimeBarCtrl_Test : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
MyControl myctrl1 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl1);

MyControl myctrl2 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl2);

MyControl myctrl3 = new MyControl();
placeUserControls.AddTimeBarSegment(myctrl3);

}
}

////////////////////**********************Error

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not
set to an instance of an object.

Source Error:

Line 54: Label lbl = new Label();
Line 55: lbl.Text = "Hello";
Line 56: tdCell.Controls.Add(lbl);
Line 57:
Line 58:

Source File: d:\inetpub\wwwroot\MACT\Interface\TimeBarCtrl.ascx.cs
Line: 56

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an
object.]
TimeBarCtrl.Page_Load(Object sender, EventArgs e) in
d:\inetpub\wwwroot\MACT\Interface\TimeBarCtrl.ascx.cs:56
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object
o, Object t, EventArgs e) +13
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object
sender, EventArgs e) +45
System.Web.UI.Control.OnLoad(EventArgs e) +80
System.Web.UI.Control.LoadRecursive() +49
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Control.LoadRecursive() +132
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
+3710

rushikesh.joshi · Mar 30, 2006

Hi Karl,

Thankyou for quick response.

Yes you are right, there might be some problem in my user control.

But it seems ok, there is tdCell id and my MyControl.ascx page and i m
trying to add some label control by just tdCell.Controls.Add(lbl).

this is working perfectly in ASPX file but this is not working in ASCX.

Thanks
Rushikesh

CaffieneRush · Mar 30, 2006

I've tested your basic code and it works just fine but you'll need to
do a bit more work to instantiate a user control programmatically.

More details here.
http://msdn2.microsoft.com/en-us/library/c0az2h86.aspx

Patrice · Mar 30, 2006

Looks like tdCell is null.

error in adding user controls at runtime

rushikesh.joshi

Karl Seguin [MVP]

rushikesh.joshi

CaffieneRush

Patrice