Question

Anyone know how I can dynamically load a control inside of a shared/static function? The function itself is inside of a mustinherit/abstract class. (It’s an ASP.NET project in VB) I want to do something like this:
VB:

    Public Shared Function GetWidget(ByVal name As WidgetName) As Control
        Select Case name
            Case WidgetName.Name1
                Return LoadControl("~/Control1.ascx")
            Case WidgetName.Name2
                Return LoadControl("~/Control2.ascx")
            Case WidgetName.Name3
                Return LoadControl("~/Control3.ascx")
        End Select
    End Function

my C# is a little rusty, so this might have some syntax errors:

Public Static Control GetWidget(WidgetName name)  
{  
    switch (name)  
    {  
        Case WidgetName.Name1:  
            return LoadControl("~/Control1.ascx");  
            break;  
        Case WidgetName.Name2:  
            return LoadControl("~/Control2.ascx");  
            break;  
        Case WidgetName.Name3:  
            return LoadControl("~/Control3.ascx");  
            break;  
    }  
}  

(Where WidgetName is an enumerator.)

I’m getting “Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.”, but I don’t understand this error. I understand what it means, I just don’t understand why calling LoadControl isn’t seen by the compiler as being an explicit instance of the class. What’s not explicit about using LoadControl to create a new control from a file? I tried creating a new user control and initializing it, then setting it to a different control with LoadControl to no avail. I also don’t want to do a DirectCast because I’m trying to put this in a shared, mustinheret (abstract) class, which therefore doesn’t have an .aspx file to write in a <%@ Reference Control="~/SomeControlPath.ascx" %>, so the class name is unavailable.

What I’m trying to do is write a static function that takes some value and returns a control based only on that control’s source file location. The end result is a user-modifiable list of controls. They get a column of controls that they freely add, remove, or reorder based on a static list of available child controls that I specify. I’m not married to this approach; it might be really wrong in more ways than one.

yeah, I know the static strings being there is code smell, it doesn’t actually look like that; it’s a simplification for the sake of asking the question.

C#, VB, or plain English explanations all welcome.

Answer 1

Is it because LoadControl can’t be returned from your class? Can you try this instead…

    Protected Static string GetWidget(WidgetName name)  
    {  
        switch (name)  
        {  
            Case WidgetName.Name1:  
                return "~/Control1.ascx";  
                break;  
            Case WidgetName.Name2:  
                return "~/Control2.ascx";  
                break;  
            Case WidgetName.Name3:  
                return"~/Control3.ascx";  
                break;  
      }  
 } 

and call the method like

... = LoadControl(GetWidget(name));

I suspect that the other alternative is to cast the control

Control c;
...
Case ...
   c = (ControlName)LoadControl("~/Control1/.ascx");
   break;
...
return c;

However the calling code would still need to cast it back to its type…