Wiring events on dynamically-loaded ASP.NET User Controls? - asp.net

Question

For a "dashboard" module I need to dynamically load user controls based on criteria as the user enters the page (role, etc). The problem is that the events are not being fired at all from the controls
As I understand it I need to load the controls in the OnPreInit method of the dashboard page, however I cannot get a reference to the Placeholder control at this point of initialization (i.e. I get a NullReferenceException); trying to load the Placeholder dynamically via Page.FindControl gives me, ironically, a StackOverflowException.
I've tried loading the controls in PreRender and OnInit as well but the events in the controls are not wired up properly and will not fire.
The code is basically this:
// this does not work; if I try to access the placeholder control itself
// ("phDashboardControls") I get a NullReferenceException, if I try
// Page.FindControl("phDashboardControls") I get a StackOverflowException
protected override void OnPreInit(EventArgs e)
{
base.OnPreInit(e);
Control ph = Page.FindControl("phDashBoardControls"); // Placeholder
if (ph != null)
{
// GetControlsToLoad just instantiates the controls and returns
// an IList<Control>. Eventually it will have logic to
// determine which control needs to be loaded based on user role etc.
foreach (Control control in GetControlsToLoad())
{
ph.Controls.Add(control);
}
}
}
// IModularControl is a custom interface defining a single
// Initialize method to set up a control...
private void Page_Load(object sender, EventArgs e)
{
foreach (Control control in this.phDashboardControls.Controls)
{
if (control is IModularControl)
((IModularControl)control).Initialize(this.CompanyID);
}
}

Answer 1

I've successfully loaded controls dynamically in Page_Load before. The only thing I found I had to be careful of was to ensure that if I did a postback, the same controls were loaded in subsequent page_load to ensure that the view state didn't get corrupted... all events etc worked as expected. In my case the controls flow ended up something like this:
page_load - load control a
(do something which causes postback and event x to fire)
page_load - make sure you load control a
event_x - clear control a, load control b
(do something which causes postback)
page_load - make sure you load control b
...
it meant loading controls you fully intented discarding, but was the only way I could find to not corrupt the viewstate...
If you have a page with PlaceHolder1 and Label1 in it, then the following code causes the button click event to fire just fine:
protected void Page_Load(object sender, EventArgs e)
{
var dynamicButton = new Button() { Text = "Click me" };
dynamicButton.Click +=new EventHandler(dynamicButton_Click);
PlaceHolder1.Controls.Add(dynamicButton);
}
void dynamicButton_Click(object sender, EventArgs e)
{
Label1.Text = "Clicked button";
}
Behaves the same with a user control:
WebUserControl ascx:
<%# Control Language="C#" AutoEventWireup="true" CodeFile="WebUserControl.ascx.cs" Inherits="WebUserControl" %>
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
<asp:Button ID="Button1" runat="server" Text="Click Me" onclick="Button1_Click" />
WebUserControl code behind:
protected void Button1_Click(object sender, EventArgs e)
{
Label1.Text = "Clicked Button";
}
parent control that loads the child control:
protected void Page_Load(object sender, EventArgs e)
{
var dynamicControl = Page.LoadControl("~/WebUserControl.ascx");
PlaceHolder1.Controls.Add(dynamicControl);
}

Answer 2

Just FYI the issue had to do with validation; the events weren't firing properly because some of the validation controls (there were a ton) weren't configured to only apply to that control.