strange event postback behaviour in dynamically created usercontrol

[Tim_Mac]

hi,
i have an aspx page which dynamically loads a user control and adds it
to a placeholder. the control is recreated and added to the
placeholder for postbacks as well.
the user control contains a datagrid and some buttons and textboxes.
the button events fire correctly and execute their code. however, the
datagrid events fire a postback, and execute Page_load in the
usercontrol, but the Item_Command code is not executed. the code to
add events to the datagrid is in InitialiseComponent.

i have the datagrid binding in UserControl_PreRender, so that it is
bound between postbacks.

can anyone suggest why the postback is happening without the
ItemCommand event happening? i've verified this with VS debugging.

thanks
tim

 

[Steven Cheng[MSFT]]

Hi Tim_Mac,

Welcome to ASP.NET newsgroup.
From your description, you've a UserControl which contains some button and
a DataGrid on it, the datagrid is subscribing some postback
events(ItemCommand). And in one of your asp.net page, you dynamically load
the usercontrol and add it on your page. However, you found the ItemCommand
of the datagrid(in usercontrol) always not fire, yes?

Based on my experience, such event handler not executing problem is likely
caused by the following things:
1. For dynamic loaded(created) controls, make sure we add them in the
Page_Init or Page_Load every time the page is requested(IsPostback or
not...).

2. For control's event handler, we also need to register them in Init or
Load event. Also, for template databound controls such as DataGrid or
DataList, we should avoid rebinding them with different datasource before
processing postback event since the event may depend on the original binded
datas.

As for your condition, since some other controls (such as button)'s event
handler execute correctly. I think the problem is likely within the
UserControl itself. Would you try registering your datagrid's ItemCommand
handler in the usercontrol's ascx template instead of programmatically
register in codebehind? Just like
<asp:datagrid ...... OnItemCommand="DataGrid_ItemCommand" ...>

If you feel it convenient, I suggest you try build a simpler usercontrol
(contains a datagrid) so as to repro the problem and send it to me. Then I
can do some researchs on my side.

In addition, if you feel necessary, I can also generate a test page on my
side and let you have a compare to see whehter there are any difference.

Please feel free to let me know if you have any questions. Thanks,

Steven Cheng
Microsoft Online Support

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(This posting is provided "AS IS", with no warranties, and confers no
rights.)

 

[Tim_Mac]

hi Steven,
thank you for your most helpful reply.
i have got it working now, and will attempt to explain how and why for
future reference.

my aspx page contaings the following in Page_Load:
Modules.SportsLadder ladder =
this.LoadControl("Modules/SportsLadder.ascx") as Modules.SportsLadder;
this.serverForm.Controls.Add(ladder);

the user control is loaded regardless of whether a postback has taken
place or not.
the user control then contains a call to if(!IsPostBack) BindGrid() in
the Page_Load.

when i would delete an item in the datagrid, the page would post back,
and Page_Load would fire, but the datagrid_itemcommand event would not
fire. the datagrid would disappear from the page.

i tried adding in a PreRender event for the usercontrol, and calling
BindGrid() there, and that kept the datagrid on screen after postbacks,
but the itemcommand event still didn't fire. what got it working was i
removed the if(!IsPostBack) from the Page_Load of the user control, so
then the datagrid is bound every time. i then had the problem of the
itemcommand event being called twice (what a surprise). the reason is
because it was set in the aspx page, as Steven suggested:
<asp:datagrid ...... OnItemCommand="DataGrid_ItemCommand" ...>
but it was also set in InitialiseComponent in code. i took it out of
the code, and let the aspx handler do it.

now it works perfectly. i didn't run into any problems re-binding the
datagrid in Page_Load, my methods were still able to identify the row
that was clicked and any of the controls in the cells.

thanks for your help.
tim