Hi All, I got a real doozy here. I have read hundreds upon hundreds offorum posts and found numerous others who have replicated this problem,but have yet to find a solution. Through testing I have been able tofind the cause of the problem, and will describe it here firsttextually and then through a code example.
Thepurpose of what I am trying to do is to create a postback-free webapplication through the use of ASP.net AJAX UpdatePanels and UserControls. When programmatically adding a User Control to a web pagethrough a normal postback everything works fine. All the controlswithin the user control are registered properly in the page and anyupdate panels included in the user control also work properly. HOWEVER,if instead of using a full postback you use an UpdatePanel and apartial page update of the UpdatePanel the controls do not getregistered with the page and events from them do not fire (forinstance, a button click event never hits the event breakpoint).
Becausethe very same user control works fine if loaded in a full postback ordynamically added from a namespace works fine, I can be relatively surethat it only is trouble when loading via a partial page update into anUpdatePanel. I load the control via the LoadConrol method and then addit to the page via a PlaceHolder control. Theoretically, adding theUser Control to the PlaceHolder should register itself and it'scontrols and events with the page, but it does not.
Thefollowing code sample is a UpdatePanel-free page using a user controlthat works, later I will show the same code with an UpdatePanel thatdoes not.
I think I need to figure out how to register thecontrols and their events with the page without going through a fullpage postback. Any suggestions??
This example works as expected:
Default.aspx:
1<%@dotnet.itags.org. Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
2
3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
4<html xmlns="http://www.w3.org/1999/xhtml">
5<head runat="server">
6 <title>Untitled Page</title>
7</head>
8<body>
9 <form id="form1" runat="server">
10 <div>
11 <asp:PlaceHolder ID="UCPlaceHolder" runat="server"></asp:PlaceHolder>
12 </div>
13 </form>
14</body>
15</html>
Default.aspx.cs:
1using System;
2using System.Data;
3using System.Configuration;
4using System.Web;
5using System.Web.Security;
6using System.Web.UI;
7using System.Web.UI.WebControls;
8using System.Web.UI.WebControls.WebParts;
9using System.Web.UI.HtmlControls;
10
11public partialclass _Default : System.Web.UI.Page
12{
13protected void Page_Load(object sender, EventArgs e)
14 {
15 Control ctl = LoadControl("~/UserControlDemo.ascx");
16 ctl.ID ="UC1";
17this.UCPlaceHolder.Controls.Add(ctl);
18 }
19}
UserControlDemo.ascx:
1<%@dotnet.itags.org. Control Language="C#" AutoEventWireup="true" CodeFile="UserControlDemo.ascx.cs" Inherits="UserControlDemo" %>
2<asp:Button ID="Button1" runat="server" Text="Display from UC" OnClick="Button1_Click" /> <br />
3<br />
4<asp:Label ID="Content" runat="server" Text="Content"></asp:Label>
UserControlDemo.ascx.cs:
1using System;
2using System.Data;
3using System.Configuration;
4using System.Collections;
5using System.Web;
6using System.Web.Security;
7using System.Web.UI;
8using System.Web.UI.WebControls;
9using System.Web.UI.WebControls.WebParts;
10using System.Web.UI.HtmlControls;
11
12public partialclass UserControlDemo : System.Web.UI.UserControl
13{
14protected void Page_Load(object sender, EventArgs e)
15 {
16 }
17protected void Button1_Click(object sender, EventArgs e)
18 {
19 Content.Text ="Content Changed.";
20 }
21}
Now,consider this variation, where instead of loading the control in thePageLoad event, you do so programmatically via a button Click event.This does not work as it cause a full postback which refreshes theplaceholder. Viewstate does not seem to be working in this case. (usesthe same user control as the previous example)
Default.aspx:
1<%@dotnet.itags.org. Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
2
3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
4<html xmlns="http://www.w3.org/1999/xhtml">
5<head runat="server">
6 <title>Untitled Page</title>
7</head>
8<body>
9 <form id="form1" runat="server">
10 <div>
11 <asp:Button ID="Button1" runat="server" Text="Load User Control" OnClick="Button1_Click" />
12 <br />
13 <br />
14 <asp:PlaceHolder ID="UCPlaceHolder" runat="server"></asp:PlaceHolder>
15 </div>
16 </form>
17</body>
18</html>
Default.aspx.cs:
1using System;
2using System.Data;
3using System.Configuration;
4using System.Web;
5using System.Web.Security;
6using System.Web.UI;
7using System.Web.UI.WebControls;
8using System.Web.UI.WebControls.WebParts;
9using System.Web.UI.HtmlControls;
10
11public partialclass _Default : System.Web.UI.Page
12{
13protected void Page_Load(object sender, EventArgs e)
14 {
15 }
16protected void Button1_Click(object sender, EventArgs e)
17 {
18 Control ctl = LoadControl("~/UserControlDemo.ascx");
19 ctl.ID ="UC1";
20this.UCPlaceHolder.Controls.Add(ctl);
21 }
22}
Tosolve this postback problem, one would naturally want to use anUpdatePanel, like the following example. However this does not work asthe controls do not seem to get registered with the page, and furthernesting of user controls in UpdatePanels (to create a postback freeapp) are no better.
Default2.aspx:
1<%@dotnet.itags.org. Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>
2
3<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
4
5<html xmlns="http://www.w3.org/1999/xhtml" >
6<head runat="server">
7 <title>Untitled Page</title>
8</head>
9<body>
10 <form id="form1" runat="server">
11 <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true"></asp:ScriptManager>
12 <div>
13 <asp:UpdatePanel ID="UpdatePanel2" runat="server">
14 <ContentTemplate>
15 <asp:Button ID="Button1" runat="server" Text="Load User Control into UpdatePanel" OnClick="Button1_Click" />
16 </ContentTemplate>
17 </asp:UpdatePanel>
18 <br />
19 <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
20 <ContentTemplate>
21 <asp:PlaceHolder ID="ContentPlaceHolder" runat="server"></asp:PlaceHolder>
22 </ContentTemplate>
23 <Triggers>
24 <asp:AsyncPostBackTrigger ControlID="Button1" />
25 </Triggers>
26 </asp:UpdatePanel>
27 </div>
28 </form>
29</body>
30</html>
Default2.aspx.cs:
1using System;
2using System.Data;
3using System.Configuration;
4using System.Collections;
5using System.Web;
6using System.Web.Security;
7using System.Web.UI;
8using System.Web.UI.WebControls;
9using System.Web.UI.WebControls.WebParts;
10using System.Web.UI.HtmlControls;
11
12public partialclass Default2 : System.Web.UI.Page
13{
14protected void Page_Load(object sender, EventArgs e)
15 {
16
17 }
18protected void Button1_Click(object sender, EventArgs e)
19 {
20 Control ctl = LoadControl("~/UserControlDemo.ascx");//loads into the page
21 ctl.ID ="UC1";
22this.ContentPlaceHolder.Controls.Add(ctl);//adds to page control tree (or at least it should)
23 }
24}
I knowI can use the "visible" property of my controls to toggle them on andoff a page to create a flicker free experience, however, my applicationis a database intensive app and I don't want the page running queriesagainst the database unless I'm absolutely sure the user wants them.Rendering a 10 forms and keeping them hidden isn't a big deal, butrunning 10 queries that the user never wants to see is, otherwise I'dstick to that method, its works perfectly. Any suggestions? Or requestsfor clarification? Any help you can provide is muchappreciated...thanks, Chris.
My suggestion is to not use an updatepanel for this. Google for ScottGu's blog on templating tricks; you can use a service to grab an ascx, feed it a datasource to populate the data then send the results to the page. use javascript to insert those results into the page DOM where needed, and code all your functionality in js or web methods of one form or another. It's a much cleaner / lower overhead way to do what you're trying to do anyway.
Hi Paul, I took a look at ScottGu blog, I believe this is the article you were referencing: http://weblogs.asp.net/scottgu/archive/2006/10/22/Tip_2F00_Trick_3A00_-Cool-UI-Templating-Technique-to-use-with-ASP.NET-AJAX-for-non_2D00_UpdatePanel-scenarios.aspx
Unfortunately this is not the solution I am looking for. By using this method I lose the main benefits of ASP.net: managed code, event based triggers, and the rest of the integrated features. I believe this method will cause the same problem, whatever I load into the page, the page won't be aware of it and no events will fire.
For now I am going to have to use postbacks, and I'll used the update panels for keeping things like sorting gridviews postback-less.
Thanks for the suggestion though!
I am having exactly the same problem
Can someone please help?
In similar situations before, I have used javascript and other hacks, but I feel reluctant to try to do it again. If we have a framework that can be used and can make work simpler, then It makes sense.
However, these kind of problems are frustrating, and I don't know what is the resolution. I am sure people mus thave encountered this before.
Can someone help?
This is more a dynamic controls problem than an AJAX problem.
When you dynamically add a control, you have to add it EVERY request. By moving it from PageLoad to Button_Click, you've stopped creating the control every request. You only create it if the button is pressed. That is why the events won't fire when you use controls within the user control -- because on the postback, the control doesn't even exist! The postback data is for a control that isn't in the control tree, because you didn't add it, because the event that adds it isn't firing again.
The technique to solve this is to utilize viewstate to remember that the control has been added, so that you can add it from the LoadViewState method. In your click handler, call a new method - LoadUserControl(). Define LoadUserControl to create and add the control, and to set a viewstate key, ViewState["LoadUserControl"] = true. Then override LoadViewState, and after calling base.LoadViewState, look for that viewstate key. If its true, call LoadUserControl().
New problem... Now its possible it will be added twice -- if you click the same button a 2nd time, LoadViewState will call it, and so will your button click handler. So add code to your button click handler to avoid creating it if its already loaded -- just check for the viewstate key.
Infinities...This is very interesting, thank you for your response! Unfortunately you lose me when you talk about overriding the LoadViewState. How would you modify the following code to accomplish what you are saying?
protected void Button_Click(object sender, EventArgs e)Thanks!
{
Control ctl = LoadControl("~/userControl.ascx");
this.Panel1.Controls.Add(ctl);
}
Ok, that sounds promising. But, I don't think the situation would work still.
I have a gridView. In every row of a gridview, one of the cells contains a nested update panel. When the user clicks on a particular row, a user control dynamically gets added to the nested update panel. This works fine.
When I click on a particular button INSIDE this user control then the postback disappears, no events are triggered and nothing happens. The fact that the control probably does not exist makes sense because it justifies what happens, as in no events are fired.
However now this user control has values and data inside it, so when you are saying to load that control again, what happens to the value and the data, it looks like that data is lost. Is that not right?
Basically, in my situation AJAX cannot help. In the first place my user control should already have a viewstate in order to persist the value of data and state of the elements inside the user control. Since its viewstate is not stored, the "re-adding" will simply not work at all.
gsinha25:
However now this user control has values and data inside it, so when you are saying to load that control again, what happens to the value and the data, it looks like that data is lost. Is that not right?
No that is not right. The fact you are loading it again doesn't mean its data is lost. All controls are reloaded every request, even the statically declared ones. ViewState maintains itself through the framework, but it only maintains the data in the control, not the control itself.
Basically, in my situation AJAX cannot help.
You would have the same problem if you were not using ajax. What you'd see is that the loaded user control would disappear after you click a button in it.
In the first place my user control should already have a viewstate in order to persist the value of data and state of the elements inside the user control. Since its viewstate is not stored, the "re-adding" will simply not work at all.
ViewState is maintained for the control. All you have to do is make sure it exists every request. It will work, trust me.
I'm sure the formatting of this is going to be off, but here's the basic idea.
protected void Button_Click(object sender, EventArgs e)
{
LoadUserControl();
}
private void LoadUserControl()
{
Control ctl = LoadControl("~/userControl.ascx");
this.Panel1.Controls.Clear();
this.Panel1.Controls.Add(ctl);
ViewState["Loaded"] = true;}
protected override void LoadViewState(object savedState)
{
base.LoadViewState(savedState);
if (ViewState["Loaded"] != null)
LoadUserControl();
}
Hi Infinities,
This is starting to make sense. I believe what you are talking about will work for my problem - in fact I often assumed it had something to do with the viewstate, however my knowledge and experience with it is limited. (I am new to C# and ASP.net, coming over from ColdFusion.) I am still a little confused on the the LoadViewState override. As I understand it, this event fires after the Init event in the lifecyle, and it's goal is to reload the user control if it has been added to the page. One question that pops up here, and may be what gsinha was referencing, does chages to the control also progress if it is reloading the control every time? For instance, if the user control is a gridview populated from a database and I have sorted and/or filtered it, would these sorts and filters be passed along as well?
Another question, when you assign the view state key in "ViewState[" "] = true" does it matter which key you use? And a final question, where is the savedState object coming from in the LoadViewState override?
Thanks again for your help!
P.S. I read your writeup at your website on the viewstate, I think i'll need to read it three or four more times before I can make sense of it all but amazing stuff, I love the attention to detail!
As I understand it, this event fires after the Init event in the lifecyle, and it's goal is to reload the user control if it has been added to the page.
The general role of LoadViewState is to deserialize the control's share of the page's entire viewstate payload. Think of viewstate as just a bunch of data -- data which is associated with each control on the page. On a postback, that data is available to the control that owns it again, if it's still around that is. The role of the code I gave you is to recreate the control if it was remembered previously that it had been created.
One question that pops up here, and may be what gsinha was referencing, does chages to the control also progress if it is reloading the control every time? For instance, if the user control is a gridview populated from a database and I have sorted and/or filtered it, would these sorts and filters be passed along as well?
Yes -- because what you have to understand is that all controls are reloaded every request. In fact, the page is completely reconstructed from the ground up every request. Remember request/response mechanism of the web is essentially a stateless process. ASP.NET and other frameworks create the feeling of statefulness through tricks like ViewState and Session state. ViewState is persisted across posts -- the controls are not. You create the control tree for the page by either statically declaring it with asp.net markup, or by dynamically creating the controls yourself. But either way, the controls start completely fresh and new every request. ViewState is then deserialized and injected into the controls, restoring them to the state they were on the last request.
Another question, when you assign the view state key in "ViewState[" "] = true" does it matter which key you use?
No -- the idea is just to remember the fact that the control was loaded. Each control's viewstate is scoped to it, so there's no risk of using a key thats already in use by some other control.
And a final question, where is the savedState object coming from in the LoadViewState override?
That is the deserialized viewstate associated with that specific control. The base implementation uses it to repopulate the keys stored in the ViewState statebag.
P.S. I read your writeup at your website on the viewstate, I think i'll need to read it three or four more times before I can make sense of it all but amazing stuff, I love the attention to detail!
Thanks for reading :) I know it's quite long... but hopefully worth it.
It works!! Thanks a bundle! This solved the most important problem I had, which was loading the user control on to the page via an Update Panel. It does however bring up a few further questions that I was hoping you could help with!
First, how do I modify your code so that I can have multiple buttons load different UCs each while still using the LoadViewState override? The following code is my best attempt at it:
Instead of using the click event to call the LoadUserControl function, I did this:
protected void LinkButton_Click(object sender, EventArgs e)
{
MainBodyPanel.Controls.Clear();
Control ctl = LoadControl("UserControl.ascx");
MainBodyPanel.Controls.Add(ctl);ViewState["Loaded"] =true;
}
And then in the override I did as you suggested, only added an addtional If statement for each button and control,
and sent it back to the click event function instead of the LoadUserControl so that each control could have its
own viewstate key.
While I can add new controls to the page, I cannot see them again once another control calls the .clear()
function an all that is left is the viewstate which then throws an error as it doesn't see the same control tree.
Is there a better way?
The second problem I have is I cannot get different user controls to communicate with each other. This is
apparent in two places. The first is I have a user control with a set of links. it is these links that call the
other user controls into the update panel dynamically. If I add the UserControl dynamically before the page
loads, the links can't see the container panel on the page. I tried using this.findControl("...").Controls.Add()
but that didn't work. So for now I have the links hard coded into the page instead being their own user control,
but it's really too complex to keep doing it that way, and it limits my nesting options.
Thanks again for any help u can provide!
Ok... help me understand :) You have a bunch of links, which when one is clicked, you want to dynamically load a user control into a particular spot. Is that 'spot' different for each link? If you click on one link and then another are there supposed to now be 2 controls on the page or does the 2nd one replace the first?
I'll assume you want only 1 control at a time.
What you described sounds like it should work. I personally wouldn't explicitly call the event handler -- thats usually a bad idea. It won't cause any problems if you know what you're doing but its better design to have a 3rd method that they both call, which gives each method a clear distinct purpose (its generally bad if you have to think... who called this method?).
One think you should definitely do is give the User Control you load a particular ID. Make the ID based on something that will (1) be exactly the same every time and (2) be different for different user controls. So for example, clicking on Link1 might load UC1.ascx with ID "uc1", and clicking Link2 might load UC2.ascx with ID "uc2". The reason for this is.. well, when you dont specify an ID, any control that requires one (textboxes for example) will use an autogenerated one. But if you load controls differently on a postback than you did on the first request, the IDs wont necessarily be the same, causing problems. Assigning an ID avoids that. You shouldn't have been getting the exception you mentioned... try what I said and let me know. If you still get it, show me some code...
About your user control communication problem... I'm not following 100%. Where and when exactly are you calling FindControl, and what control are you trying to find? With controls whenever you find yourself trying to get two of them to talk directly to each other... well its usually a sign that you could improve your design a bit. The control should be self sufficient, it shouldn't be broken because something else on the page isnt just so. Rather than have the control talk to the other control, you can have it raise an event. The page then listens for the event and decides what to do with it (something which the original control doesn't much care about), which may be to push something into another control on the page (the origin of which that control doesn't much care about). Much less coupled that way.
"I'll assume you want only 1 control at a time." correct assumption. there is a panel placeholder that the controls get swapped in and out of.
I tried adding the ID as you suggested but the exception still came up. Here is the code as it currently stands:
1protected void ViewCustomerListLinkButton_Click(object sender, EventArgs e)2 {3 MainBodyPanel.Controls.Clear();4 Control ctl = LoadControl("~/UserControls/CustomersControls/CustomerList.ascx");5 ctl.ID ="CustList";6 MainBodyPanel.Controls.Add(ctl);78 ViewState["CustList"] =true;9 }1011protected void AddCustomerLinkButton_Click(object sender, EventArgs e)12 {13 MainBodyPanel.Controls.Clear();14 Control ctl = LoadControl("~/UserControls/CustomersControls/CustomerAdd.ascx");15 ctl.ID ="CustAdd";16 MainBodyPanel.Controls.Add(ctl);1718 ViewState["CustAdd"] =true;19 }2021protected override void LoadViewState(object savedState)22 {23base.LoadViewState(savedState);2425if (ViewState["CustList"] !=null)26 ViewCustomerListLinkButton_Click(null,null);2728if (ViewState["CustAdd"] !=null)29 ViewCustomerListLinkButton_Click(null,null);3031 } The exception is thrown because when I click on a second link, it Clears the MainBodyPanel control list, and the viewstate is looking for the control list that includes the now removed control. I tried various ways I could think of to remove the viewstate but to no avail...
"What you described sounds like it should work. I personally wouldn'texplicitly call the event handler -- thats usually a bad idea. It won'tcause any problems if you know what you're doing but its better designto have a 3rd method that they both call, which gives each method aclear distinct purpose (its generally bad if you have to think... whocalled this method?)."
I couldn't figure out a way to do this. I was having each click event pass the url via the function call LoadUserControl("~/control.ascx") but I couldn't figure out how to have the loadviewstate override pass the url back when needed, so I did it as you see above.
About the communication problem, in more detail, the problem is actually with the code above. Right now that is in my pages code behind, if i make those links into a user control, and then add the control to the page with those functions in the controls code behind, it cannot see the container panel (which in this case is the MainBodyPanel). I tried using the find control method but it still couldn't see it. With the links and event handlers hard coded it works fine.
Thanks!
With this code, once you click on one of the buttons, that control will always be loaded. When you click on one button you need to 'clear' the viewstate key of the other, otherwise you'll be trying to load both controls all the time. Pretty sure that is why you are getting the error, too. Easier if you just use the same key with a different value.
About the event handler thing...
protected void Link1_Handler(object sender, EventArgs args) { Foo(); }
private void Foo() { /* load Foo, set ViewState["Loaded"] = 1 */ };
protected void Link2_Handler(object sender, EventArgs args) { Bar(); }
private void Bar() { /* load Bar, set ViewState["Loaded"] = 2 */ };
protected override void LoadViewState(object savedState) {
base.LoadViewState(savedState);
if(ViewState["Loaded"] == 1) {
Foo();
}
else if(ViewState["Loaded"] == 2) {
Bar();
}
}
You might be tempted to store the path to the actual UserControl in ViewState, that way you can just LoadControl(ViewState["Loaded"]) ... but, don't :) Treat ViewState like user input. Don't trust it. If you did it that way, the user could maniuplate viewstate in such a way that they could cause any user control in your site to load, rather than be restricted to the two you want.
Ok... so I'm still confused about your links problem. You have each link as a user control, and when clicked you want them to load their content into the parent? Controls should not modify their parent's controls. It would be better like I said, to have an event raised by the control. The page, which contains all these link controls, just hooks that event on each control and then loads the control into the appropriate place. Your FindControl probably isn't working because FindControl only finds controls within the current naming container. User controls are naming containers. So when you say, this.FindControl("foo") from within a UserControl, you're only looking for a control named "foo" WITHIN the user control, not higher. To go higher you have to call FindControl on a control thats higher. But you still have to be careful with naming containers. You could start at the page level with this.Page.FindControl("foo"), but that will only find controls named "foo" that are children of page or children of non-naming containers in page. Imagine if you had a user control that contained control with ID "foo", and then you put 5 of them on the page. Which would you expect Page.FindControl("foo") to find? Its ambiguous -- thats why it won't find ANY. Each Foo is within a naming container, so their actual IDs are "uc1$foo", "uc2$foo", etc (where uc1=id of user control 1). If you know for sure the control will be in a particular place (for you it sounds like in a master page), then go ahead and hard code that ID... but be warned, its a fragile way to do it. Another approach is to have your Page expose a "MasterContainer" property of type Control. The user controls can then just say ((MyPageType)this.Page).MasterContainer.Controls.Add(), and it will work so long as the control is on a page that inherits from "MyPage" (which, all of your pages could inherit from).Ad infinitum... lots of different ways to deal with it.
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