Recently I had to put together a SharePoint 2008 Web Part and I wanted to use a User Control for the UI and pass the various Web Part settings into it. The “standard” way to call LoadControl doesn’t allow us to pass any parameters:
There is an additional overload that takes a Type and a list of parameters but using that doesn’t seem to initialise any of the designer created bits, so referencing any of the sub-controls fails with a null reference exception.
One solution would be to add some public properties to the control, create it using the normal LoadControl, set the properties to the relevant values and display it. I wasn’t too keen on that approach so instead I created a LoadControl extension method on TemplateControl that provides the following overload:
Extension Method Implementation
The implementation of the extension methoid is very straightforward. Firstly we take the params we are passed and pull out their types into an array:
Type[] paramTypes = new Type[constructorParams.Length]; for (int paramLoop = 0; paramLoop < constructorParams.Length; paramLoop++) paramTypes[paramLoop] = constructorParams[paramLoop].GetType();
Once we have the types we can use GetConstructor to lookup the constructor that matches our signature:
var constructor = control.GetType().BaseType.GetConstructor(paramTypes);
Then if our constructor was found, we simply invoke it:
constructor.Invoke(control, constructorParams);
User Control
In our user control code behind we add our required constructor, but we also need to add a default constructor (one with no parameters) or the compiler gets confused and you will get a CS1729 runtime error:
public partial class TestControl : System.Web.UI.UserControl
{
public TestControl()
{
}
public TestControl(Color color1, Color color2)
{
Label1.ForeColor = color1;
Label2.ForeColor = color2;
}
}
And that’s it! A demo with the extension method class and a sample user control is available here:
I’m a firm believer that reading and “best practices” are no substitute for using your brain! 
The zip file’s corrupt. Could you email it to me?
Seems fine to me, what are you opening it with?
Just a note, the extensionless file in the zip is really a compressed file too. Just rename it, or tell it to open with zip/winrar or whatever you use. Youll then find the sln + code
@Ron Thanks for the comment. I’ve just redownloaded and opened it with WinRAR and it looks just fine to me, which is wierd. What are you opening it with?
WinZip won’t open the file.
I’ve just downloaded WinZIP and opened it just fine, and I’ve also tried it in WinRAR, 7Zip and the built in Windows ZIP folder functionality just fine?
Thanks a lot for this! It helped me a lot today
I loves reflection… thanks for the post!
What if i didnt know explicitely what the usercontrol was before runtime.
Currently i have a dynamically loaded usercontrol and will need to be able to pass parameters to the usercontrol pending on user selected choices preceding the loading of the usercontrol.
Data.uControl = LoadControl(core.Type.tostring & “.ascx”)
….
Dim par As Control = Me.Parent
par.Controls.Add(Data.uControl)
There’s not a lot you can do about that John. The only possible solutions I can think of off the top of my head are revert to reflection, have a horrible case statement to construct the relevant type or try and abstract all of the UserControls to a common interface.
Aloha Steven!
Thank you for excellent solution!! I’ve been searching for 2 days for a way to generically implement User Controls, as well as pass them strongly typed data. I’d first tried introducing an interface. That solved the first part but not the second. Your solution works well with both!
P.S. I haven’t yet tackled the issue of transferring user entered data from the User Control back to the form but hope to solve this part soon too.
This was a big help. THANKS Steven!
If you are getting an error then pls change extension code like below,
//var control = templateControl.LoadControl(controlPath) as UserControl;
UserControl control = templateControl.LoadControl(controlPath) as UserControl;
clever solution
thnx
Very cool, thanks!
Hi everyone I am developing a data entry form with different questions for different users. how can i dynamicaly add the different questions on page load in vb.net? i’m still learning vb.net.any ideas
Thanks for the simple n smart solution.
It saved me a lot of time…thanks!!