I have a ListView control which is exhibiting an odd behaviour - rows are only partially updating after a postback. I'm hoping someone here can shed some light on why this might be occuring.
My listview DataSource is bound to a List of items which is stored in the page session state. This is intentional, partially to timeout out-of-date views since multiple users view the data. On a plain resort operation, the sorting is handled on page via javascript, and the list/session data order is kept in sync via callbacks. Callback also checks for permissions levels. On a particular resort operation that is more complicated, the javascript on the page makes a postback to the page to handle the sorting logic. The List/Session is updated as in the callback, then the listview control is rebound to the data. The page loads again, and the rows show the new order. No problem, right?
The problem is that some of the elements in the listview do not change value in accordance with the new order. While the hyperlinks and text that is processed on page (ie like <%# Eval("ProjectAbbrev") %>) are updated appropriately, checkboxes, literals, and dropdowns that have their values set via the OnItemDataBound event method are not - they stay "frozen" in place, even though stepping through the code reveals that the method is run during the postback, and that the controls SHOULD be set to their new values. If I go and manually truncate the list to say, half the original size, sure enough only those items are repopulated, but the checkboxes and such still retain their original values.
So my question is: Why aren't these elements updating along with the rest of the listview control elements on the postback? I have the feeling that I'm either misunderstanding the page lifecycle in ASP.NET or that I've encountered a bug of some kind.
At this point I'm thinking I will have to move the more complicated sorting operation to the page in javascript, but that will be rather tricky and I'd like to avoid doing so if possible.
UPDATE: I have tried setting EnableViewState to false and it does not fix this. I couldn't use that tactic in any case because other parts of the page (save) rely on reading the viewstate in the end.
UPDATE: I'm providing some code snippets in the hope that they might shed some light on this issue:
Page: The HyperLink element will update properly after postback, but the CheckBox which has its value assigned in the OnQueueRepeater_ItemDataBound method, will stay the same.
<%# Control Language="C#" AutoEventWireup="true" CodeBehind="TextProcessorProjects.ascx.cs" Inherits="ETD.UI.Controls.TextProcessorProjects" %>
<asp:ListView ID="QueueListView" runat="server" OnItemDataBound="OnQueueRepeater_ItemDataBound">
<ItemTemplate>
<tr>
<td><asp:HyperLink runat="server" ID="ProjectIDLink"><%# Eval("ProjectAbbrev") %></asp:HyperLink></td>
<td><asp:CheckBox runat="server" ID="ScannedCheckBox" BorderStyle="None" /></td>
</tr>
</ItemTemplate>
</asp:ListView>
Code behind: On postback, the following code executes:
protected List<Book> QueueDataItems
{
get { return (List<Book>)Session["Queue"]; }
set { Session["Queue"] = value; }
}
else if (IsPostBack && !Page.IsCallback)
{
// resort QueueDataItems List appropriately
ResortQueue(Request.Params)
// rebind
QueueListView.DataSource = QueueDataItems;
QueueListView.DataBind();
}
protected void OnQueueRepeater_ItemDataBound(object sender, ListViewItemEventArgs e)
{
// ...
// ... other controls set
CheckBox scannedCheckBox = e.Item.FindControl("ScannedCheckBox") as CheckBox;
scannedCheckBox.Checked = book.Scanned;
}
UPDATE: I've given up on getting this to work and moved my sorting logic to the client side with javascript. If anyone has any ideas as to why this odd behaviour was happening though, I'd still be very interested in hearing them!
out of interest, what point on the page are you databinding on? Page_Load?
Try it on OnPreRender - might help out.
Sounds like the ViewState is kicking in and repopulating the data.
In any case, if you are Databinding in every postback anyways, you should probably set the EnableViewState of your ListView to false to reduce page size.
I think this is related to the order of when the different events are triggered during the page lifecycle. See ASP.NET Page Life Cycle Overview. You should do databinding in Page_OnPreRender to make sure the replopulating is done after control events (that will cause data updating) on the page.
Maybe your QueueListView is getting re-bound for some reason.
Try resetting the DataSource value after the DataBind() to see what happens
QueueListView.DataBind();
QueueListView.DataSource = null;
Any chance this could be a caching issue? I ran into a similar issue using a listview with an XMLDatasource. I tried turning off all the viewstate. I would bind the listview in the code behind and use XPath to write it all out to the screen on my aspx page. This was used in a search....the next time I did a search, none of the new information showed up. The reason is because an XMLDatasource has caching enabled by default. In my case I was hitting the DB every time and had no need to cache it. I turned off the caching on the datasource and all my problems were fixed.
I only mention this because the error I was having sounds identical to yours. I can't see how you're retrieving book in the itemdatabound - and you're not using an XML Datasource by the looks of things.....but I thought the comment might trigger something for you. Good luck....though it sounds like you've already moved on :-).
Is the checkbox control ReadOnly=true or Enabled=false?
I have had trouble with controls with one of these properties set as above not updating no matter how I try to manhandle the control in the code behind. I would think disabling the viewstate would also bypass that little "feature" of ASP.NET, but it's worth a shot.
Also, if the items are sorted via clientside code, is that ordering preserved on the postback? I don't think that you can alter the CLR object you have in session via javascript.
Not sure if this helps, replace <%# Eval("ProjectAbbrev") %> with the Hyperlink.Text assigned in the OnQueueRepeater_ItemDataBound method and see if all rows get populated correctly.
This probably won't solve your problem, but will be interesting to know the result.
Related
I'm trying to build a very specific search page for a project and I'm having lot of trouble dealing with multiple postbacks invoked by dynamically-generated controls on a single page.
The page has to work like this:
There is a single checkbox, "Detailed search", that causes a postback on checking/unchecking.
When detailed search is not active, a simple grid with contents and buttons is displayed. Nothing special.
When detailed search is active, N checkboxes must be generated from some dynamic data, that represent the sections where you want the search to happen. Below the checkboxes, an AJAX-enabled tab control will appear, initially with no tab pages.
When checking one of the section checkboxes, a postback will occur. After the postback, data will be searched in the section selected by the user, then a new tab page containing a grid view of results and the name of the section will be added to the tab control. If the checkbox is unchecked, the tab page will disappear from the control, again, after a postback.
Now, the issue is that pretty much everything has to be generated dynamically, and that pretty much everything is connected to something else.
First issue: dealing with the "Detailed search" checkbox. Sounds easy, doesn't it? My initial idea was to set Page.Viewstate["DetailedSearchEnabled"] to true or false during the check/uncheck event handler, then create controls dynamically checking the value of DetailedSearchEnabled during Page_Load.
Nope. The postback event-handling happens between Page_Load and Page_LoadComplete. It would take an additional refresh for things to work as intended.
<< Then I'll just generate the controls on Page_LoadComplete! >>
Nope. Those controls need event handling as well, and if they're generated after Page_Load they will not be wired up correctly.
A possible solution would be generating everything in advance, on Page_Load, and only hiding/showing controls on Page_LoadComplete. But that is inefficient, and one important point of this search page is that only the minimum amount of controls should be generated.
The difficulty of this task seems to come from the way event wiring and the page life cycle work.
Surely there must be a better way of approaching this problem.
First issue: dealing with the "Detailed search" check box.
The correct approach (if you want to use page post-backs) is as follows:
In the CheckChanged event handler, save the value of the Checked property to ViewState["DetailedSearchEnabled"]. If the value is true, add the dynamic check boxes to the page. If the value is false, find and remove them.
Override LoadViewState. After calling base.LoadViewState, re-create the dynamic check boxes and wire up their events if ViewState["DetailedSearchEnabled"] is true. Note that neither Page_Load nor Page_LoadComplete is the appropriate place to do this.
Yes, you should create the dynamic check boxes at two points in the page life cycle. I recommend a helper method.
In general, your event handlers should add or remove just the dynamic controls (if any) affected by those particular events, but LoadViewState should re-create all dynamic controls that existed from the previous page request. You must store enough information in view state for LoadViewState to do so.
My answer to this other question demonstrates how to add and remove dynamic controls. You may want to use it as a reference.
Sounds to me like you should be using a CheckBoxList control to handle your dynamic checkboxes. You can add an remove items to the CheckBoxList during your post back and not have to worry about dynamically adding/removing actual controls/events to the form.
Here is a link to the msdn:
https://msdn.microsoft.com/en-us/library/14atsyf5(v=vs.85).aspx
Here is some sample code:
Protected void Button1_Click (object sender, System.EventArgs e)
{
CheckBoxList.Items.Add(new ListItem("TextValue1", "Value1"));
CheckBoxList.Items.Add(new ListItem("TextValue2", "Value2"));
}
If all else fails, you could still fall back on the quick-and-dirty old-fashioned ASP way.
Use Response.Write or <%...%> to generate your dynamic controls as plain old HTML (simple form fields, e.g. <input type="checkbox" name="foo" value="1" />).
Make sure you have a form field for every piece of information you may need after the postback(s). If necessary, use hidden form fields to 're-post' values across subsequent postbacks.
After postback, retrieve the values of the controls with the Request object.
Use those values to adjust the generation of controls as you see fit.
You should be able to do all of this in Page_Load. The advantage is total freedom. The disadvantage is total freedom to make a big mess of your aspx. So you may want to migrate all this dirty code out of your aspx, and into a custom-made control, which you can then add to your aspx.
When generating your own HTML, be careful not to introduce XSS vulnerabilities. Use HtmlEncode where necessary.
As you suggested yourself, there is a better way to tackle it.
If I was in the same situation, I would create web methods for interacting with the page, and use client side to do the UI. I'm currently working mostly with angular JS, although it does come with a learning curve. You could use ng-hide/ng-show to bind to the checkbox event to display the detailed search. When the n number of checkboxes needs to be displayed, you can then just fill them in with ng-repeat, for each of the items you need to display, after a check/uncheck you can dynamically populate new controls etc. through web method calls if extra data is needed.
Pure ASP postbacks are quite clunky from my experience, and not really suited for building a maintainable dynamic UI.
Instead of making so many postbacks, it would be better to use jquery and ajax calls to load the controls as needed and then attach events to it or you can even use UpdatePnael for that. Help Links:
https://www.simple-talk.com/dotnet/asp.net/ajax-basics-with-jquery-in-asp.net/
http://encosia.com/using-jquery-to-directly-call-aspnet-ajax-page-methods/
Yes, I realize that's a bit of a vague title but I'm having a hard time stating the problem. I have a .Net .aspx page that has a Master page, some Ajax, and an updatepanel. My problem occurs on 2 different pages but in both cases I'm either selecting a radio button or a checkbox when the behavior occurs. Immediately after selection the entire page moves down. It does not scroll but instead it is like an extra tag was inserted into the source. I have done HTML source comparisons before and after this change and nothing is different. I can only assume it is related to the updatepanel but I cannot determine where this may be happening.
I'd be happy to provide more information if you can direct me towards a solution.
Thanks!
I am not entirely sure if this will do it and there is not enough detail here to be sure, but have you tried setting RenderMode to inline on the UpdatePanel? Maybe that will do the trick. Otherwise go take a look at Fiddler and see what is coming back from the server. Alternate recommendation (if none of the above work) is to just get your result in Json and change the markup yourself with jQuery or something like it.
Incredible. This was exactly the problem. I've modified my code as follows and form stays in place after selection. This was a simple case of selecting a radio button and having it auto-populate a dropdownlist.
[asp:UpdatePanel ID="panelValidation" runat="server" ChildrenAsTriggers="true" UpdateMode="Always" RenderMode="Inline"]
[ContentTemplate]
[asp:ValidationSummary ID="ValidationSummary1" runat="server"]
[ContentTemplate]
[asp:UpdatePanel]
Thanks!
I have a ListView in a web form (c#/.net 4.0). There is an ImageButton in the ItemTemplate.
After a postback, the ItemCommand event fires... and then everythings stops. No other page events occur. (Actually there is one other thing: Dispose() from ExtenderControlBase runs right after the event code finishes - this site has some AjaxControltoolkit controls, though there are none on this particular page).
There are a lot of things involved here so it's not really practical to post all the code, but generally, is there anything that could cause this?
I am rebinding the ListView on each postback, because I'm handling paging on the server side. When I assign the data source to the ListView, it's initially going to have no rows. So at the time the command event fires, the DataSource has no data in it, since it hasn't yet been loaded from the database and rebound. I can't think why this would cause the entire page to just stop loading, though.
The template is just this:
<ItemTemplate>
<tr>
<td class="DataListRow"><asp:ImageButton ID="edit" runat="server" ImageUrl="~/images/nav/datagrid_edit.gif" CommandName="edit" />
</td>
// a few orther cells
</tr>
</ItemTemplate>
Thoughts?
Doesn't sound right to me.
In these situations, I take an approach like this:
First, make sure the page is checked into source control or otherwise backed up.
If possible, create an new page and copy in just the controls and associated code that is blowing up. See if it works in isolation. If it doesn't work in isolation, well, you've isolated the problem.
If you can't do that due to complexity, or if the code works fine in isolation, go to your problem page and start ripping out all the other functionality. Seriously. Systematically remove controls and features on by one, starting with whatever is the most complex.
Eventually, after one of your changes the abberant behavior will stop, and whatever you removed last is in some way the culprit. See if you can get a fix together.
Roll back and apply the fix.
This hasn't failed me yet.
I'm adding a dynamically built set of checkboxes to an asp.net page from the code behind with something like this in a recursive fashion:
pnlPageAccessList.Controls.Add(myCheckboxControl);
The controls show up fine on the page, but they don't show up when I view source, nor can I access them from the code behind.
If I add the controls in the on_init method, they work. But I have some business rules driving changes to the list of controls itself that require I fire the add method elsewhere.
Has anyone seen this before? I'm away from work so I can't copy the exact code.
I have two terrible ideas for how to get it working. One involves some jQuery and a set of hidden controls holding a big array of integers; the other is run the method on_init AND on my other events so the controls at least show up. Both smell like ugly hacks. The second one I suspect won't work to read the values out of the checkboxes.
On the server side the page is recreated from scratch every postback, so if you add any controls dynamically, you have to re-add them on every postback.
As you add the controls at runtime they are not known at compile time, so there is no variables declared for the controls in the Page object. If you want to access the controls you either have to keep the reference from when you create the controls, or locate them in the Controls collection where you put them.
If you can set the ID for the checkbox controls you can use the FindControl method from code behind to retrieve the control instances.
#Anero is right that you can add an ID and use FindControl.
You can also use a checkbox list, and add checkboxes to that list. Then they're already in a predefined control in your markup and code-behind.
You don't say where the method has to be fired, but once they're added dynamically, they do have to be added on every postback. You probably have a little more flexibility than just adding them at the Init event, as long as you stay aware of where things like validation occurs (if it matters in this case), or where you want to handle the checkbox contents. You can defer as late as PreRender for getting checkbox content.
Well, looks like I'm going to have to do it clientside. Thanks for the answers. I'd be able to do it On_Init, but doing it clientside with a hidden control is gonna save me a lot of overhead and be more flexible moving forward.
If anyone's curious, here's the jQuery for finding all the checked checkboxes and putting their value attribute into a hidden control in a comma delimited list:
<script type="text/javascript">
$(document).ready(function () {
$('[id*=PagesPanel]').find(':checkbox').click(function () {
$('[id*=PagesPanel]').find(':checked').each(function () {
$('[id*=lblHiddenPageArray]').append($(this).val() + ", ");
});
});
});
</script>
I know there is a similar problem on this forum, but the solutions did not really work for me. I am populating form controls with fields from a few different data sources, and the data shows up great.
I have an ImageButton control, which has an OnClick Event set to grab all of the data from the form. Unfortunately, when I click the button, it seems as though the page is reloading first, and THEN is executes the OnClick call. The data that was hand-entered, or hard-coded seems to be pulled fine from the controls it was entered in, but anything that was pulled from a datasource is not able to be read. Any ideas. this is the last hurdle in a project that I have been working on for 6 months.
Are you talking about drop downs or gridviews? When are you binding data, on page load?
Good design will have you bind your data upon page load but only in
if(!isPostBack){
dropdown.databind()
gridview.databind()
}.
Otherwise it will rebind every page load. If its not reloading you can get selected values from those controls if thats what your looking for.
An alternative is to set your data source and databind in your aspx page with a datasource object. That automates the above automatically.
Have you enabled viewstate on your controls? Posting code samples would go a long way to helping solve your issue.
When you click on a bottom in asp.net at first all the page Events take place like Page_Load and ... and then the event happens ( in this case Click).
But because everything is loading again, I think that you have a !isPostback in your code that you use to bind the data, you should remove that in order to get your data every time.
Or if it is not the solution please post some code and more description for the problem
Actually, it is hiddenfields, dropdowns, labels, and textfields. I just tried doing the binding in the init, and the load, but no dice. When I tried binding it on !isPostBack only, none of the fields showed up.
I think one of the main problems is that the dataset I am getting is from a method call to an API. I receive the data fine, but it comes in programmatically, then I have to do all of the control-setting programmatically as well. Would you like to see the code for ideas? Thank you for helping, no one is working today!
Jason