In ASP.NET Web Forms, you often have pages that need to display different user controls ( .ascx ) dynamically based on some condition (like a menu selection or query string parameter). Instead of creating separate pages for each control, you can load them dynamically at runtime using LoadControl and a switch-case structure.
Scenario
Suppose you have multiple user controls:
Dashboard.ascx
NewClient.ascx
AddNewClient.ascx
masterList.ascx
…and many others
You want to load these controls into a placeholder ( ControlHolder ) in your Default.aspx page based on a numeric or string parameter.
Implementation Steps
1. Add a Placeholder in ASPX Page
In your ASPX page ( Default.aspx ), add a PlaceHolder control where dynamic controls will be loaded:
<asp:PlaceHolder ID="ControlHolder" runat="server"></asp:PlaceHolder>
This placeholder acts as a container for your user controls.
2. Load Controls Dynamically in Code-Behind
In your code-behind ( Default.aspx.cs ), you can use a switch-case statement to determine which .ascx control to load:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string pageID = Request.QueryString["PageID"] != null ? Request.QueryString["PageID"].ToString() : ""; // Example: get value from URL ?PageID=1
LoadUserControl(pageID);
}
}
private void LoadUserControl(string pageID)
{
switch (pageID)
{
case "1":
Dashboard dashboared_ctrl = (Dashboard)LoadControl("Dashboard.ascx");
ControlHolder.Controls.Add(dashboared_ctrl);
break;
case "2":
NewClientmaster newclient_ctrl = (NewClientmaster)LoadControl("NewClient.ascx");
ControlHolder.Controls.Add(newclient_ctrl);
break;
case "3":
AddNewClientList addnewclient = (AddNewClientList)LoadControl("AddNewClient.ascx");
ControlHolder.Controls.Add(addnewclient);
break;
case "4":
UCCmasterList uccmaster_ctrl = (UCCmasterList)LoadControl("masterList.ascx");
ControlHolder.Controls.Add(uccmaster_ctrl);
break;
case "5":
AddClientList addclient_ctrl = (AddClientList)LoadControl("AddClientList.ascx");
ControlHolder.Controls.Add(addclient_ctrl);
break;
case "6":
ViewIPOMaster viewipo_master = (ViewIPOMaster)LoadControl("ViewMaster.ascx");
ControlHolder.Controls.Add(viewipo_master);
break;
case "7":
AddIPOMaster addipomastr = (AddIPOMaster)LoadControl("AddMaster.ascx");
ControlHolder.Controls.Add(addipomastr);
break;
case "8":
AddIPO addipo = (AddIPO)LoadControl("AddIPO.ascx");
ControlHolder.Controls.Add(addipo);
break;
case "9":
UpdateExchangeIPO updateEx = (UpdateExchangeIPO)LoadControl("Update.ascx");
ControlHolder.Controls.Add(updateEx);
break;
case "10":
OrderList orderlist_ctrl = (OrderList)LoadControl("OrderList.ascx");
ControlHolder.Controls.Add(orderlist_ctrl);
break;
case "11":
UPIReport upireport_ctrl = (UPIReport)LoadControl("Report.ascx");
ControlHolder.Controls.Add(upireport_ctrl);
break;
case "12":
IPOSettingsOffline offlinesetting_ctrl = (IPOSettingsOffline)LoadControl("Settings.ascx");
ControlHolder.Controls.Add(offlinesetting_ctrl);
break;
case "13":
OfflineOrders offlinelist_ctrl = (OfflineOrders)LoadControl("Orders.ascx");
ControlHolder.Controls.Add(offlinelist_ctrl);
break;
case "14":
IPOAllotment ipoallotment_ctrl = (IPOAllotment)LoadControl("Allotment.ascx");
ControlHolder.Controls.Add(ipoallotment_ctrl);
break;
case "15":
ExchangePage ExchangePage_ctrl = (ExchangePage)LoadControl("ExchangePage.ascx");
ControlHolder.Controls.Add(ExchangePage_ctrl);
break;
case "16":
ViewIssue ViewIssue_ctrl = (ViewIssue)LoadControl("ViewIssue.ascx");
ControlHolder.Controls.Add(ViewIssue_ctrl);
break;
case "17":
ViewIPO ViewIPO_ctrl = (ViewIPO)LoadControl("ViewIPO.ascx");
ControlHolder.Controls.Add(ViewIPO_ctrl);
break;
default:
// Optionally show a default control or message
ControlHolder.Controls.Add(new LiteralControl("<p>Select a valid option</p>"));
break;
}
}
3. How It Works
Get the Page Identifier: You can use QueryString , a DropDownList , or any parameter to determine which control to load.
Switch-Case Logic: Each case corresponds to a specific .ascx control. The control is loaded dynamically and added to the placeholder.
Type Casting: (Dashboard)LoadControl("Dashboard.ascx") casts the loaded control to the correct class so you can access its public properties or methods.
Adding to Placeholder: ControlHolder.Controls.Add(dashboared_ctrl) adds the control to the page dynamically at runtime.
4. Advantages of this Approach
Single ASPX page for multiple views: Reduces code duplication.
Dynamic content loading: Only loads the control needed based on user interaction.
Maintainability: Adding new controls is simple — just add a new case in the switch.
Encapsulation: Each user control handles its own UI and logic.
5. Optional Enhancements
Use QueryString or Session for persistence.
Default control: Show a welcome dashboard if no PageID is provided.
Error handling: Wrap LoadControl in try-catch to prevent runtime errors.
Refactor using Dictionary : For large numbers of controls, you can use a dictionary mapping instead of long switch-case.
Example URL to Load Controls
Default.aspx?PageID=1 -> Loads Dashboard.ascx
Default.aspx?PageID=2 -> Loads NewClientmaster.ascx
Default.aspx?PageID=10 -> Loads OrderList.ascx
Conclusion
Using switch-case with LoadControl in ASP.NET Web Forms is an efficient way to dynamically load multiple user controls into a single ASPX page, making your application modular and maintainable.