Question

I have an extension method like this:

<Extension()>
Public Function Trim(value As Object, MaxLength As Integer) As String
    If value IsNot Nothing AndAlso value.ToString.Length > MaxLength Then
        Return value.ToString.Substring(0, MaxLength)
    Else
        Return value.ToString
    End If
End Function

My assumption was that I could then go Eval("MyColumnName").Trim(20) when databinding (Rather then doing things like MyMethod(Eval(“MyColumnName”)) but this has proved incorrect.

Is there any way to use extension on the Eval method?

PS: I have my extensions referenced as a global reference

Answer 1

It turns out that while you can extend the Object type, you can’t use a variable of type Object to call the method.

MSDN Magazine: Basic Instincts: Extension Methods

Dim myString As String = "ABC123"
Dim myObject As Object = "ABC123"
Dim myResult as String

myResult = myString.Trim(3)  ' Works
myResult = myObject.Trim(3)  ' Fails

So I think the best you could hope for in a one-liner is:

Eval("MyColumnName").ToString.Trim(20)