ASP.Net: User controls added to placeholder dynamically cannot retrieve values

asp.netpostbackuser-controls

I am adding some user controls dynamically to a PlaceHolder server control. My user control consists of some labels and some textbox controls.

When I submit the form and try to view the contents of the textboxes (within each user control) on the server, they are empty.

When the postback completes, the textboxes have the data that I entered prior to postback. This tells me that the text in the boxes are being retained through ViewState. I just don't know why I can't find them when I'm debugging.

Can someone please tell me why I would not be seeing the data the user entered on the server?

Thanks for any help.

Best Answer

This is based on .NET v1 event sequence, but it should give you the idea:

Initialize (Init event)
Begin Tracking View State (checks if postback)
- Load View State (if postback)
- Load Postback Data (if postback)
Load (Load event)
- Raise Changed Events (if postback)
- Raise Postback Events (if postback)
PreRender (PreRender event)
Save View State
Render
Unload (Unload event)
Dispose

As you can see, the loading of ViewState data back to the controls happen before the Load event. So in order for your dynamically-added controls to "retain" those values, they have to be present for the ASP.NET page to reload the values in the first place. You would have to re-create those controls at the Init stage, before Load View State occurs.

Related Solutions

C# – “The Controls collection cannot be modified because the control contains code blocks”

First, start the code block with <%# instead of <%= :

<head id="head1" runat="server">
  <title>My Page</title>
  <link href="css/common.css" rel="stylesheet" type="text/css" />
  <script type="text/javascript" src="<%# ResolveUrl("~/javascript/leesUtils.js") %>"></script>
</head>

This changes the code block from a Response.Write code block to a databinding expression.
Since <%# ... %> databinding expressions aren't code blocks, the CLR won't complain. Then in the code for the master page, you'd add the following:

protected void Page_Load(object sender, EventArgs e)
{
  Page.Header.DataBind();    
}

R – ASP.NET: How to destroy dynamically added User Control

The OnClick event happens after the Page_Load event in the Page Life Cycle. On a postback the user controls Page_Load event will still be called. If you put the Clear() command later in the parent page life cycle, that should help.

EDIT As per your update. The reason that the Page_Load of the user control is happening every time is because you have the code to add that control to the page in the Page_Load event of your .aspx page. Basically, every time the page is requested, that user control is going to be added to the page(and hit the user control Page_Load event).

If you want a certain action to happen/not happen on a postback use the IsPostBack property of the page. Not sure exactly what you want to do with the page, but hopefully that helps a little bit.

Best Answer

Related Solutions

C# – “The Controls collection cannot be modified because the control contains code blocks”

R – ASP.NET: How to destroy dynamically added User Control

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