I'm trying to edit a textbox's text in a Page_Load form on an ASP.NET page, but when I try to edit TextBox1.Text it throws a NullReferenceException because the TextBox has not yet been instantiated. Specifically what I'm trying to implement is this: http://www.codeproject.com/KB/user-controls/popupcalendarcontrol.aspx but it is written for an older version of ASP.NET and does not work for me. Is there a way to instantiate the controls at the start of Page_Load? or another event that I can catch on load? With a normal windows form I would call InitializeComponent() in the constructor.
There are absolutely different events you can attach to but it sounds like the page isn't loading the controls properly because they should be available by that point. You can take a look at the ASP.NET Page Life Cycle for more information.
Does the TextBox sit within a bound control, such as a FormView, GridView, DataList, etc? If so, then the control won't exist until after the databinding happens. Once that event happens, you can do something like
DirectCast(myDataList.SelectedRow.FindControl("myTextBox"),
TextBox).Text
I know that I am a bit behind in getting to this question BUT I have found something unusual that I can NOT find documented anywhere. It would appear that IF your page is "under" a Master Page, and IF you refer to ANYTHING on said master page, the controls to your current page are null - EVERYONE of them. I found this out by referencing "Master.Environment" - a public string - during my InitializeCulture method and having the FIRST control on my current (Default.aspx) page be null during Page_Load() - WHATEVER the first control was.
I know I am late but if this can help ANYBODY, I want the word out.
Related
I understand that this will causes a page reload (partial or full, depending on how your UpdatePanels are set up)
But,
where in the code I should put it (client or server side)?
which control should I send to the method? Is it must be inside the UpdatePanel?
does this method work only for controls inside update panels?
must the control have a postback capability?
what is the engine behind this? How does this method work, so I could use it properly.
Thanks.
The function call returns a string of executable JavaScript, which you need to write to the client somewhere in your response.
Typically, you're sending your Page (this/Me) unless you have a control that you specifically want to handle the postback (ie, that implements IPostBackEventHandler)
GetPostBackEventReference is not related to UpdatePanels; if you have one, it will handle the postback.
No (see #2)
This makes a postback to the page. If you want it to raise an event when it posts back, you need to implement IPostBackEventHandler, either on your page or on one of your controls.
http://msdn.microsoft.com/en-us/library/ms153112.aspx
In my asp .net C# project I have a page defualt.aspx on which I have placed 2 components.
So in all I have:
1) default.aspx (main page, not doing much code in it)
2) wuc_Lookup.ascx (doing a lot here, grabbing data, setting session, etc)
3) wuc_PageMessages.ascx (has a couple of panels and labels for message output
)
The intent is to use 3) in any page in my application. 1) and 2) are already working. My issue is that the Page_Load sequence is:
1st default Loads
2nd wuc_pageMessage loads
3rd wuc_lookup loads
The problem with this is that The wuc_pageMessage is relevant only after wuc_lookup runs.
My intent was not to put code in Page_Load for the message wuc_pageMessage control because I wanted to be able to call a method to post the message during the component load of wuc_lookup. I do this because only after wuc_lookup do I set the session which I use for the message value.
I actually got values showing up if I put the code in wuc_lookup to manipulate the code-in-front server control (panels and labels) using this.parent.findControl syntax...
But then when I try to rip that code and put it into the code-behind for wuc_pageMessage, and then call the method from the wuc_lookup it has fallen out of scope or context...
So I tried to change this.Parent by passing httpContext.current.handler as casting it as page...that didn't work...then I tried passing Object sender from the calling component...that didn't work either. Neither of them had the Parent property and or it was null which led me to believe that once the wuc_PageMessages.ascx loaded it was a dead deal until a repost happens and that is ugly and something I don't want to do.
I am having some implementation issues and I am not sure what to do. I have been stunk on this for eight hours and Is there just something I am not seeing?
I want to keep away from spagetti code. I don't want to have to scatter code-behind in 3 different files. Theoretically I should only need 2 of these to talk to eachother. i don't want code-behind in default..it's basically just a container. I want to trigger the wuc_pageMessage from wuc_Lookup.ascx without having it be "in" wuc_Lookup.ascx (peer web user controls) I want that to always be a peer relationship. Any advice would be great ...thanks...
Try moving the wuc_PageMessages logic from the page_load to the page_prerender event.
If you are going to use the preRender you would do it on the default.aspx preRender because this event fires after the wuc_lookup. Prerender will not fire on the components for some reason. So yes, this only solves part of the issue. I am not sure how you would get the alreeady loaded component of wuc_PageMessages to get back into scope. If you try to reference components on a component that has already loaded, you will get a null, like they are not there or not in scope anymore... anyone have any ideas?
I have a shared user control. This UC is in one page and everything works fine. In the second page, the RadTextBox client-API get_value() method reports "", when it has a legitimate value. There is very little javascript on that page, and it's not targeting textboxes; it's in a page with 6 tabs. The controls work fine; I have RadCombo's and the drop downs work as you would expect. But no text, no selected value, nothing is being reported (I have a script to check if the page is an empty form). How do I even debug this to figure out what is going on, and why the value isn't being reported?
Thanks.
My advice is to start with debugging your js code and see whether the telerik inputs' client objects are valid in your context. If so, rhe methods from their client API should return the values set from the end user.
It was a duplicate method name in a user control,copied twice, so that's why it was bombing. Thanks.
I'm trying to get the values of dynamically generated FileUpload controls that I add to a Panel:
<asp:Panel ID="pFileControls" runat="server">
</asp:Panel>
I create the controls during a loop through a record set:
foreach(DataRow dr in ds.Tables[0].Rows)
{
FileUpload fu = new FileUpload();
fu.ID = dr["SomeID"].ToString();
pFileControls.Controls.Add(fu);
}
Everything works fine up to the point where I submit the form with this button:
<asp:Button ID="btnImportFile" runat="server" Text="Save" OnClick="btnImportFile_Click" />
Which I register like this (Page_Load):
ScriptManager.GetCurrent(this).RegisterPostBackControl(btnImportFile);
I do this because I'm using a MasterPage/ContentPage setting in my website and mostly everything happens inside an UpdatePanel for AJAXification purposes. Bear in mind that if I explicity specify a FileUpload Control in the HTML view, it works 100%.
When the form is submitted I try to iterate the Panel like this:
foreach (Control ctrl in pFileControls.Controls)
{
if (ctrl.GetType() != typeof(FileUpload))
{
continue;
}
//Do the saving of the file here
}
Except, the Panel seems to only return one control: The Content Place Holder for the page and nothing else. Does anyone have some ideas about this?
What part of the life cycle are you adding the dynamic controls?
if you are putting them in the page_load it may be too late, try putting the generation of the dynamic controls into the page_init and see if that fixes the problem.
page lifecycle
http://msdn.microsoft.com/en-us/library/ms178472.aspx
dynamic controls
http://geekswithblogs.net/shahed/archive/2008/06/26/123391.aspx
Note:
"Its recommended to load the dynamic
controls during the Page_Init instead,
because we may want to hook up our
events with proper handler at an early
stage. ... Do not assigning
properties of a dynamic control
(viewstate enabled), during Page_Init,
it will not be reflected. "
I would expect that even with the update panel, you will need to be mindful of the page_load limitations with dynamic controls.
let me know if this helps or if I missed the mark!
Let's try a different course of action (I've gotten dynamic file upload to work, but it was a bear and I wish I had simply used this)
http://www.asp.net/ajaxlibrary/act_AsyncFileUpload.ashx
or
http://en.fileuploadajax.subgurim.net/
these may not create a 'loop' of elements, but you can simply keep loading docs on a as-needed basis.
I have specifically used
http://www.asp.net/ajaxlibrary/act_AsyncFileUpload.ashx
to great effect.
There also appear to be some limitations to the update:panel and the file upload, check out these sites.
(this one says it does not work in partial update status but does work in full postback)
http://forums.asp.net/p/1105208/1689084.aspx
do you know if the submit is triggering the full page or just the update:panel? (check out this: http://geekswithblogs.net/mmintoff/archive/2009/04/01/fileupload-within-updatepanel.aspx
I'm presently in the process of reworking a MultiViewControl based wizard process for our web application. I am having an rough time trying to make sense of the order that events are happening (Page_Load, Init, prerender, etc). Does anyone out there on the interwebs have details on dealing with one of these controls? Please don't just say 'google' it. I've done that and have yet to find a good, comprehensive site yet.
Admittedly, I haven't really elaborated on the problems I'm having with this control, so I'll try to do that:
Primary problem is the initialization of UserControls that live in different Views. In the existing codebase, the programmer was using a combination of multiviewcontrol.ActiveViewIndex = WHATEVER and Response.Redirect("PageWithMultiView.aspx?nextstep") and it made it all very convoluted. My task is to attempt to remove the Response.Redirect calls and use only the setting of the ActiveViewIndex. Is this even possible? Also, there are some cases where I need to initialize a control in a particular view only on the initial load and not on subsequent postbacks. I can use something like the IsPostBack flag but this is only ever set to false on the initial load. Subsequent reloads IsPostBack == true. I basically want to have IsPostBack set to false for the initial load of each View. Can this be done without doing a Response.Redirect to itself?
Hopefully this will make some sense to someone out there.
Thanks.
Greg.
I am having an rough time trying to
make sense of the order that events
are happening (Page_Load, Init,
prerender, etc).
Here you have all details about ASP.NET page lifecycle and events: http://msdn.microsoft.com/en-us/library/ms178472.aspx .
In terms of MultiView - you should NEVER use Response.Redirect when you work with MultiView.
If user can not switch to previous view then you can check previous ActiveViewIndex value before setting it to the new value, e.g.
if (mv.ActiveViewIndex != newIndex)
{
// this view is displayed for the first time
}
If user can switch to the previous views, I suggest to place an information about already used views in session or by placing hidden field on the form with ids of the views that have already been displayed and to use that information instead of IsPostBack.