How to use ASP.Net server controls inside of Substitution control? - asp.net

Question

while the method we use in Substitution control should return strings, so how is it possible to use a donut caching in web forms on a server control which should be rendered server side?
for example Loginview control?

Answer 1

UPDATE
This is now a fully working example. There a few things happening here:
Use the call back of a substitution control to render the output of the usercontrol you need.
Use a custom page class that overrides the VerifyRenderingInServerForm and EnableEventValidation to load the control in order to prevent errors from being thrown when the usercontrol contains server controls that require a form tag or event validation.
Here's the markup:
<asp:Substitution runat="server" methodname="GetCustomersByCountry" />
Here's the callback
public string GetCustomersByCountry(string country)
{
CustomerCollection customers = DataContext.GetCustomersByCountry(country);
if (customers.Count > 0)
//RenderView returns the rendered HTML in the context of the callback
return ViewManager.RenderView("customers.ascx", customers);
else
return ViewManager.RenderView("nocustomersfound.ascx");
}
Here's the helper class to render the user control
public class ViewManager
{
private class PageForRenderingUserControl : Page
{
public override void VerifyRenderingInServerForm(Control control)
{ /* Do nothing */ }
public override bool EnableEventValidation
{
get { return false; }
set { /* Do nothing */}
}
}
public static string RenderView(string path, object data)
{
PageForRenderingUserControl pageHolder = new PageForUserControlRendering();
UserControl viewControl = (UserControl) pageHolder.LoadControl(path);
if (data != null)
{
Type viewControlType = viewControl.GetType();
FieldInfo field = viewControlType.GetField("Data");
if (field != null)
{
field.SetValue(viewControl, data);
}
else
{
throw new Exception("ViewFile: " + path + "has no data property");
}
}
pageHolder.Controls.Add(viewControl);
StringWriter result = new StringWriter();
HttpContext.Current.Server.Execute(pageHolder, result, false);
return result.ToString();
}
}
See these related questions:
Turn off page-level caching in a
user control
UserControl’s RenderControl is
asking for a form tag in (C#
.NET)

Answer 2

One thing Micah's answer left out is that the substitution function must be static, accept a HttpContext parameter, and return a string. See this msdn page for more info.
I've also extended Micah's helper class to be a little more flexible.
Markup
<asp:Substitution ID="Substitution1" MethodName="myFunction" runat="server" />
Implemenation
public static string myFunction(HttpContext httpContext){
ViewManager vm = new ViewManager();
//example using a Button control
Button b = new Button();
b.Text = "click me"; //we can set properties like this
//we can also set properties with a Dictionary Collection
Dictionary<string,object> data = new Dictionary<string,object>();
data.add("Visible",true);
String s = vm.RenderView(b,data); //don't do anything (just for example)
//we can also use this class for UserControls
UserControl myControl = vm.GetUserControl("~mypath");
data.clear();
data.add("myProp","some value");
return vm.RenderView(myControl,data); //return for Substitution control
}
Class
using System.IO;
using System.ComponentModel;
public class ViewManager
{
private PageForRenderingUserControl pageHolder;
public ViewManager()
{
pageHolder = new PageForRenderingUserControl();
}
public UserControl GetUserControl(string path)
{
return (UserControl)pageHolder.LoadControl(path);
}
public string RenderView(Control viewControl, Dictionary<string, object> data)
{
pageHolder.Controls.Clear();
//Dim viewControl As UserControl = DirectCast(pageHolder.LoadControl(Path), UserControl)
if (data != null) {
Type viewControlType = viewControl.GetType();
dynamic properties = TypeDescriptor.GetProperties(viewControl);
foreach (string x in data.Keys) {
if ((properties.Item(x) != null)) {
properties.Item(x).SetValue(viewControl, data[x]);
}
}
}
pageHolder.Controls.Add(viewControl);
StringWriter result = new StringWriter();
HttpContext.Current.Server.Execute(pageHolder, result, false);
return result.ToString();
}
private class PageForRenderingUserControl : Page
{
public override void VerifyRenderingInServerForm(Control control)
{
// Do nothing
}
public override bool EnableEventValidation {
get { return false; }
// Do nothing
set { }
}
}
}
Thanks again to Micah for the code

Answer 3

I'm fairly certain you can't do this - the Substitution control will only allow you to insert a string into an outputcached page.
This makes sense if you think about the whole output of a server control, which could be a <table> that'll disrupt all your carefully crafted markup and/or something that requires a load of <script> injected into the page - whereas injecting a single string is something that's relatively straightforward.