Dynamically loaded User Controls - problem with button_click event

  • Thread starter Thread starter Tim T
  • Start date Start date
T

Tim T

[this is a simplified / clearer explanation of an earlier post - hopefully
someone can help!]

Hi,
I have the need to use dynamically loaded user controls in a webform page.
I have the controls loading dynamically, and that part works fine. this is
the code used in a webform to dynamically load one of several controls:
private void btnCategory_Click(object sender, System.EventArgs e)

{
Control myControl = LoadControl(DropDownList1.SelectedItem.Text +
".ascx");
PlaceHolder1.Controls.Add(myControl);
}

That part works fine, selecting an item from the dropdown loads the relevant
control perfectly into the placeholder on the hosting page.

The dynamically loaded control has its own form and button within it. when a
user fills out the form and clicks the 'send' button, the button_click event
within the control is supposed to do some work and add the form data to a
DB.

My problem is that when the button from within a dynamically loaded control
is clicked, nothing happens for that event. All that happens is the page
hosting the control is reloaded, and the control disappears.

I must add that when the same control is added to a test page, everything
works fine as planned - the click event for the button does as it is
supposed to - so there is nothing wrong there. The problem is arising
because this is a DYNAMICALLY loaded control sitting in a placeholder.

I hope someone can see my exact problem and knows the solution. I'm sure it
is something simple, but am new to .NET and am stuck.
Any help greatly appreciated.

Tim..
 
Just did add something on earlier post and saw the more recent one after
that.

Well does the page you are dynamically have its own form and on select you
load a user control with its own form.

I think there might be some issues with more than one form (I remember
reading it a few days back when I started with web controls)



Regards,



HD
 
When the page reloads after the postback do you reset the
value of the placeholder?

I have found that you need to make sure that the
information is only reset when you want it to be and not
on every page refresh.
-----Original Message-----
Just did add something on earlier post and saw the more recent one after
that.

Well does the page you are dynamically have its own form and on select you
load a user control with its own form.

I think there might be some issues with more than one form (I remember
reading it a few days back when I started with web controls)



Regards,



HD



Tim T said:
[this is a simplified / clearer explanation of an earlier post - hopefully
someone can help!]

Hi,
I have the need to use dynamically loaded user controls in a webform page.
I have the controls loading dynamically, and that part works fine. this is
the code used in a webform to dynamically load one of several controls:
private void btnCategory_Click(object sender, System.EventArgs e)

{
Control myControl = LoadControl (DropDownList1.SelectedItem.Text +
".ascx");
PlaceHolder1.Controls.Add(myControl);
}

That part works fine, selecting an item from the
Click to expand...
dropdown loads the
relevant
control perfectly into the placeholder on the hosting page.

The dynamically loaded control has its own form and
Click to expand...
button within it. when
a
user fills out the form and clicks the 'send' button,
Click to expand...
the button_click
event
within the control is supposed to do some work and add the form data to a
DB.

My problem is that when the button from within a
Click to expand...
dynamically loaded
control
is clicked, nothing happens for that event. All that happens is the page
hosting the control is reloaded, and the control disappears.

I must add that when the same control is added to a test page, everything
works fine as planned - the click event for the button does as it is
supposed to - so there is nothing wrong there. The problem is arising
because this is a DYNAMICALLY loaded control sitting in a placeholder.

I hope someone can see my exact problem and knows the
Click to expand...
solution. I'm sure
it
is something simple, but am new to .NET and am stuck.
Any help greatly appreciated.

Tim..
Click to expand...


.
Click to expand...
 
Tim T said:
[this is a simplified / clearer explanation of an earlier post - hopefully
someone can help!]

Hi,
I have the need to use dynamically loaded user controls in a webform page.
I have the controls loading dynamically, and that part works fine. this is
the code used in a webform to dynamically load one of several controls:
private void btnCategory_Click(object sender, System.EventArgs e)

{
Control myControl = LoadControl(DropDownList1.SelectedItem.Text +
".ascx");
PlaceHolder1.Controls.Add(myControl);
}

That part works fine, selecting an item from the dropdown loads the relevant
control perfectly into the placeholder on the hosting page.

The dynamically loaded control has its own form and button within it. when a
user fills out the form and clicks the 'send' button, the button_click event
within the control is supposed to do some work and add the form data to a
DB.

My problem is that when the button from within a dynamically loaded control
is clicked, nothing happens for that event. All that happens is the page
hosting the control is reloaded, and the control disappears.

I must add that when the same control is added to a test page, everything
works fine as planned - the click event for the button does as it is
supposed to - so there is nothing wrong there. The problem is arising
because this is a DYNAMICALLY loaded control sitting in a placeholder.

I hope someone can see my exact problem and knows the solution. I'm sure it
is something simple, but am new to .NET and am stuck.
Any help greatly appreciated.
Click to expand...

When you say the user control has its own form, do you mean it has another
<form> element within it? If so, do you really need that?
 
I am guessing that the problem is in the hosting form. You should post your
Page_Load code so we can take a look at that. You most likely have a problem
that can be solved by moving some code into a ...

if(!(IsPostBack))
{
....
}

section of code.

I hope that helps a bit.
 
Thanks Adam,
doing as you suggested enables a control placed in a placeholder to work
from within the page propertly as i need,
But now I have a new problem. I still can't do what I am trying to achieve
because the control I want to load into the placeholder is determined by
what a user selects from a dropdown in the [hosting] page.

I put the code loading the control into a Page_Init sub as suggested, it
works when i statically Load a control by hard coding the control name in
the LoadControl("test.ascx"), but i need it to load the control dynamically

here is the sub:

private void Page_Init(object sender, System.EventArgs e)
{
if(Page.IsPostBack)
{
string controlName = DropDownList1.SelectedItem.Text; //the text for
dropdown items is the control to load
Control myControl = LoadControl(controlName+".ascx");
PlaceHolder1.Controls.Add(myControl);
}
}

the page is posted back when a user selects form the dropdown and clicks a
button, here is the sub that handles the button click:

private void btnCategory_Click(object sender, System.EventArgs e)
{
selectecdCategory.Text = DropDownList1.SelectedItem.Text.Replace("
","").Replace("/","").Replace("&","");

}

when the user selects a categroy and clicks the button, the page posts back,
I get this error

I get the following error:

"Object reference not set to an instance of an object. "

for this line:
string controlName = DropDownList1.SelectedItem.Text;

So the DropDownList1 object is not initialised before the Page_Init sub
fires.

Can you see what i am trying to achieve? any further suggestions
appreciated.
Thanks to everyone for their input so far.

Tim..
 
Thanks HD,
There is only one <form runat="server"> tag on the page hosting the control,
no form tag in the user control, i meant form fields and a button

I think i'm getting closer to solving the problem, have done what Adam
Carden suggested and that works for loading controls into place holders, but
i am still having trouble getting them to load dynamically. i may have to
try a different approach soon!

Tim

HD said:
Just did add something on earlier post and saw the more recent one after
that.

Well does the page you are dynamically have its own form and on select you
load a user control with its own form.

I think there might be some issues with more than one form (I remember
reading it a few days back when I started with web controls)



Regards,



HD



Tim T said:
[this is a simplified / clearer explanation of an earlier post - hopefully
someone can help!]

Hi,
I have the need to use dynamically loaded user controls in a webform page.
I have the controls loading dynamically, and that part works fine. this is
the code used in a webform to dynamically load one of several controls:
private void btnCategory_Click(object sender, System.EventArgs e)

{
Control myControl = LoadControl(DropDownList1.SelectedItem.Text +
".ascx");
PlaceHolder1.Controls.Add(myControl);
}

That part works fine, selecting an item from the dropdown loads the relevant
control perfectly into the placeholder on the hosting page.

The dynamically loaded control has its own form and button within it.
Click to expand...
when
a
user fills out the form and clicks the 'send' button, the button_click event
within the control is supposed to do some work and add the form data to a
DB.

My problem is that when the button from within a dynamically loaded control
is clicked, nothing happens for that event. All that happens is the page
hosting the control is reloaded, and the control disappears.

I must add that when the same control is added to a test page, everything
works fine as planned - the click event for the button does as it is
supposed to - so there is nothing wrong there. The problem is arising
because this is a DYNAMICALLY loaded control sitting in a placeholder.

I hope someone can see my exact problem and knows the solution. I'm sure it
is something simple, but am new to .NET and am stuck.
Any help greatly appreciated.

Tim..
Click to expand...
Click to expand...
 
I do have a solution to the other part of your problem, however it may
not be what you want to here.

As control events fire after page_init you could not use them to
dynamically load control in page_init.


You will still be doing a postback so it should be ok.

->In page_init

If Request.Form("dropdownaction") = True Then
'Load the control specified in the named drop down
(your placeholder control)

Panel1.Controls.Add(UserControl.LoadControl(Request.Form("<thenameofyour
dropdowncontrol>"))
End If

->In your page/control with the control selector
(within the <form> </form>)

<input type=hidden name=dropdownaction value=false>

-> As an attibute added to your dropdownlist
onchange="loadcontrol();"

-> As a script block on the page
<script langauge="javascript">
function loadcontrol() {
yourform.dropdownaction = "true";
yourform.submit();
}
</script>

I know the example is not complete, nor actually working as I have
little time. I do hope it helps.

The gist of the matter is as postbacks post the form all standard
selects (which is what drop downs render as) still pass the selected
value when the form is posted.

You can access both request.querystring and request.form in page_init so
you can get the control value from there and load the correct control.
 
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