>I would like have .NET feature like EVAL() in VFP in my application.
>

>IF EVAL(UDFExpr)
>*** Do something
>ENDIF
>

>
>Also, any tool that allow user to build expression using UI (just like filter expression in foxfire! and stonefield query) ?
>
>Or, any other way to do this in .NET?

In .NET, such issue would have to be resolved with Reflection. Here is an example that takes the class name as well as the method name from a DBF:

    ' expO1 Data provider
    Private Function ProcessTaskQuery(ByVal toDataProvider As Framework.Framework.Data) As Boolean
        Dim lcClass As String = ""
        Dim lcMethod As String = ""
        Dim lnCounter As Integer = 0
        Dim loAssembly As System.Reflection.Assembly
        Dim loMethod As System.Reflection.MethodInfo
        Dim loObject As Object
        Dim loParameterClass(1) As Object
        Dim loRow As DataRow
        Dim loType As System.Type

        loParameterClass(0) = oApp
        loParameterClass(1) = Me

        ' Establish the reference to the EXE
        loAssembly = System.Reflection.Assembly.LoadFrom(oApp.cStartupDirectory + "Robot.exe")

        ' Scan each task to execute
        For lnCounter = 0 To toDataProvider.nCount - 1
            loRow = toDataProvider.oDataSet.Tables("Temp").Rows(lnCounter)
            Status.Text = "Processing " + Trim(loRow("Title")) + "..."
            lcClass = Trim(loRow("Class"))
            lcMethod = Trim(loRow("Method"))
            Try

                ' Get a reference to the class
                loType = loAssembly.GetType("Robot." + lcClass)
                loObject = Activator.CreateInstance(loType, loParameterClass)

                ' Get a reference to the method
                loMethod = loObject.GetType().GetMethod(lcMethod)

                ' Call the method
                loMethod.Invoke(loObject, Nothing)

            Catch loError As Exception
                oApp.ErrorSetup(loError)
                Return False
            End Try
        Next

        Return True
    End Function