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Tip of the Day
Language: VB7
Expertise: Intermediate
Nov 4, 2002



Building the Right Environment to Support AI, Machine Learning and Deep Learning

A command-line Object Browser that uses Reflection

' This code is taken from Francesco Balena's
' "Programming Microsoft Visual Basic .NET" - MS Press 2002, ISBN 0735613753
' You can read a free chapter of the book at 
' http://www.vb2themax.com/HtmlDoc.asp?Table=Books&ID=101000

Imports System.Reflection

Module MainModule

    Sub Main()
        ' Get command-line arguments.
        Dim args() As String = Environment.GetCommandLineArgs()
        Dim cmd As String = Environment.CommandLine
        Dim ty As Type
        Dim mbrTypes As MemberTypes = MemberTypes.All
        Dim mbrName As String = ""
        Dim mi As MemberInfo

        ' If no arguments, /? or /help
        If args.Length <= 1 OrElse args(1) = "/?" OrElse String.Compare(args(1), _
            "/help", True) = 0 Then
            ' Show command-line syntax and exit.
            Console.WriteLine("Command-line Type Browser - by Francesco Balena")
            Console.WriteLine("   Syntax:  typebrow typename [membername[*]]")
            Exit Sub
        End If

        Dim i As Integer = args(1).IndexOf(","c)
        If i < 0 Then
            ' Create the type as specified by first argument.
            ty = Type.GetType(args(1), False, True)
            ' Create the assembly specified in the last part of the first 
            ' argument
            Dim asmname As String = args(1).Substring(i + 1)
            Dim asm As [Assembly] = [Assembly].LoadWithPartialName(asmname)
            ' Get the type in the specified assembly.
            ty = asm.GetType(args(1).Substring(0, i), False, True)
        End If

        If ty Is Nothing Then
            ' Exit if error.
            Console.WriteLine("Unable to create type ""{0}""", args(1))
            Exit Sub
        End If

        ' If the user asked for a particular name.
        If args.Length > 2 Then
            ' Retrieve the name
            mbrName = args(2)
        End If

        ' Get the list of member info to be displayed
        Dim minfos() As MemberInfo = ty.FindMembers(mbrTypes, _
            BindingFlags.Public Or BindingFlags.Instance Or BindingFlags.Static, _
            AddressOf CustomMemberFilter, mbrName)

        ' Display information on all these members.
        For Each mi In minfos
    End Sub

    ' This is the custom filter for members.
    ' On entry filterCriteria holds the name of the member we're looking for.
    ' (Supports partial names with a trailing asterisk, as in "Repl*".)
    Function CustomMemberFilter(ByVal m As MemberInfo, _
        ByVal filterCriteria As Object) As Boolean
        ' Discard accessor methods for properties.
        If m.Name.StartsWith("get_") Or m.Name.StartsWith("set_") Then
            Return False
        End If

        ' Get the search filter in uppercase.
        Dim search As String = filterCriteria.ToString.ToUpper
        If search = "" Then Return True

        If search.EndsWith("*") Then
            ' If there is a trailing asterisk, checks for partial match.
            If m.Name.ToUpper.StartsWith(search.Substring(0, _
                search.Length - 1)) Then Return True
            ' Otherwise search for exact match.
            If m.Name.ToUpper = search Then Return True
        End If
    End Function

    ' Return the syntax for a member (field, property, methods, event).
    Function MemberDescription(ByVal mi As MemberInfo) As String
        Dim res As String

        ' Different treatment for different types
        Select Case mi.MemberType
            Case MemberTypes.Field
                ' Fields: append As clause.
                Dim fdi As FieldInfo = CType(mi, FieldInfo)
                res &= NameDescription(mi, fdi.IsStatic) & VBTypeDescription _

            Case MemberTypes.Property
                ' Properties: append parameter list and return type.
                Dim pri As PropertyInfo = CType(mi, PropertyInfo)
                res &= NameDescription(mi, False) & ParamListDescription _
                res &= VBTypeDescription(pri.PropertyType)

            Case MemberTypes.Method
                ' Methods: append parameter list and return type.
                Dim mti As MethodInfo = CType(mi, MethodInfo)
                res &= NameDescription(mi, mti.IsStatic) & ParamListDescription _
                If Not (mti.ReturnType Is Nothing) Then
                    res &= VBTypeDescription(mti.ReturnType, True)
                End If

            Case MemberTypes.Constructor
                ' Constructor
                Dim cti As ConstructorInfo = CType(mi, ConstructorInfo)
                res &= NameDescription(mi, False) & ParamListDescription _

            Case MemberTypes.Event
                ' Events: append parameter list.
                Dim evi As EventInfo = CType(mi, EventInfo)
                ' Get the type that corresponds to the underlying delegate.
                Dim delType As Type = evi.EventHandlerType
                Dim mi2 As MethodInfo = delType.GetMethod("Invoke")
                res &= NameDescription(mi, False) & ParamListDescription _
        End Select

        Return res
    End Function

    ' Return a description for name.
    ' (Including Shared and member type description.)
    Function NameDescription(ByVal mi As MemberInfo, ByVal IsStatic As Boolean) _
        As String
        Dim res As String

        ' Prefix with Shared if necessary
        If IsStatic Then
            res = "Shared "
        End If

        ' Append member type, but distinguish between Sub and Function
        If mi.MemberType <> MemberTypes.Method Then
            ' if not a method, we can simply use the Enum.Format method.
            res &= [Enum].Format(mi.MemberType.GetType, mi.MemberType, _
                "G") & " "
            Dim meth As MethodInfo = CType(mi, MethodInfo)
            If meth.ReturnType.Name = "Void" Then
                res &= "Sub "
                res &= "Function "
            End If
        End If

        ' Append name and return to caller.
        If mi.MemberType = MemberTypes.Constructor Then
            ' Visual Basic constructors are named "new"
            res &= "New"
            ' A non-constructor element.
            res &= mi.Name
        End If

        Return res
    End Function

    ' Return the description for a list of parameters.
    Function ParamListDescription(ByVal pinfos() As ParameterInfo) As String
        Dim res As String = "("
        Dim i As Integer

        ' Iterate over all parameters.
        For i = 0 To pinfos.GetUpperBound(0)
            ' Append description for this parameter.
            res &= ParamDescription(pinfos(i))
            ' Append a comma if this isn't the last argument.
            If i < pinfos.GetUpperBound(0) Then res &= ", "
        ' Close the parenthesis and return to caller.
        Return res & ")"
    End Function

    ' Return a description for a single parameter.
    Function ParamDescription(ByVal pi As ParameterInfo) As String
        Dim res As String
        Dim pt As Type = pi.ParameterType

        ' Start with Optional if necessary.
        If pi.IsOptional Then res = "Optional "

        ' Append ByVal or ByRef.
        If pt.IsByRef Then
            res &= "ByRef "
            res &= "ByVal "
        End If

        ' Append the parameter name.
        res &= pi.Name
        ' Append the type, but convert it to VB syntax.
        res &= VBTypeDescription(pt)

        ' Append the default value, if there is one.
        If pi.IsOptional Then
            ' Enclose the default value within quotes if it is a string.
            If pt Is GetType(System.String) Then
                res &= " = """ & pi.DefaultValue.ToString & """"
                res &= " = " & pi.DefaultValue.ToString
            End If
        End If

        ' Return to the caller.
        Return res
    End Function

    ' Return a parameter type in VB-friendly format.
    Function VBTypeDescription(ByVal ty As Type, _
        Optional ByVal PostfixArrayMarks As Boolean = False) As String
        Dim res As String

        ' Get the return type as a string.
        res &= ty.Name
        ' Drop trailing "[]" pair, is there is one.
        If res.EndsWith("[]") Then
            res = res.Substring(0, res.Length - 2)
        End If
        ' Drop trailing *, if there is one.
        If res.EndsWith("*") Then
            res = res.Substring(0, res.Length - 1)
        End If

        ' Adjust for VB-friendly names.
        Select Case res
            Case "Int16"
                res = "Short"
            Case "Int32"
                res = "Integer"
            Case "Int64"
                res = "Long"
            Case "Void"
                ' this is the type "returned" by Sub
                Return ""
        End Select

        ' Append "AS" and "()" if this is an array.
        If Not ty.IsArray Then
            res = " As " & res
        ElseIf PostfixArrayMarks Then
            ' Append trailing () pair.
            res = " As " & res & "()"
            ' Prefix leading () pair.
            res = "() As " & res
        End If

        ' Return to the caller.
        Return res
    End Function

End Module
Francesco Balena
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