Pass Out an Object Array in .NET

Question

I'm writing a wrapper class to expose a subset of the functionality of a .NET FTP library edtftpne from Enterprise Distributed Technologies.

When you call the edtftp's GetFileInfos method you get an array of FTPFile objects returned. I'm able to iterate through these but I don't know how to pass them on as a new and different object array containing only Name and Size for each file. Here's the code I have. Sorry it's a little confusing because I have my own class named FTPFile and the .NET library I'm using also has a class named FTPFile. I'm using both of them here. I should probably change the name of my class just to avoid confusion:

Public Function GetFileList() As FTPFile() Implements IFTP.GetFileList
    Dim ftpfiles() As EnterpriseDT.Net.Ftp.FTPFile
    ftpfiles = fCon.GetFileInfos 'Fill object array
    Dim f As EnterpriseDT.Net.Ftp.FTPFile
    Dim t As FTPFile = New FTPFile 'My custom class to hold FileName and FileSize for Each file
    For Each f In ftpfiles
        'What do I do here to put these in my GetFileList array?
    Next
End Function

I'm also baffled on how to write my own FTPFile class so that this function can assign properties to each object it creates but the external COM code will see the properties of my FTPFile class as ReadOnly.

Here's what my FTPFile class looks like:

Public Interface IFTPFile
    ReadOnly Property FileSize() As Long
    ReadOnly Property FileName() As String
End Interface

<ClassInterface(ClassInterfaceType.None)> _
Public Class FTPFile : Implements IFTPFile
    Private sFileName As String = ""
    Private lFileSize As Long

    Public ReadOnly Property FileName() As String Implements IFTPFile.FileName
        Get
            FileName = sFileName
        End Get
        'Set(ByVal value As String)
        '    sFileName = value
        'End Set
    End Property

    Public ReadOnly Property FileSize() As Long Implements IFTPFile.FileSize
        Get
            FileSize = lFileSize
        End Get
        'Set(ByVal value As Long)
        '    lFileSize = value
        'End Set
    End Property
End Class

Maybe I'm going about this totally wrong. I'd just pass on the object array that I'm getting from the GetFileInfos method but COM clients won't have access to the class/object EnterpriseDT.Net.Ftp.FTPFile without me rewriting it, I'm assuming.

You can alias your class to make it easier to read: Imports MyFTPFile = EnterpriseDT.Net.Ftp.FTPFile; — Snowbear
– Snowbear, Commented Mar 25, 2011 at 22:27

Guffa · Accepted Answer · 2011-03-25 23:19:17Z

1

You have to create the array that you want to return, then you create objects for the array inside the loop:

Public Function GetFileList() As FTPFile() Implements IFTP.GetFileList
  Dim ftpfiles() As EnterpriseDT.Net.Ftp.FTPFile
  ftpfiles = fCon.GetFileInfos
  Dim result(ftpfiles.Length - 1) As FtpFile
  For i As Integer = 0 to ftpfiles.Length - 1
    result(i) = New FTPFile(ftpfiles(i).FileName, ftpfiles(i).FileSize)
  Next
  Return result
End Function

Add a constructor to the FTPFile class so that you can set the properties when you create each instance:

Public Sub New(name As String, size as Long)
  sFileName = name
  lFileSize = size
End Sub

Note: It's not recommended to use hungarian notation to specify data type in variable names. VB is a typed language, so it's not so important to keep track of the data types that you have to clutter up the variable names with it.

edited Mar 25, 2011 at 23:19

answered Mar 25, 2011 at 22:32

Guffa

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4 Comments

HK1 Over a year ago

Your code looks promising but I'm seeing a raft of errors that I'm not able to fix. The first error occurs in the line beginning Dim Result. It says "Argument not specified for parameter Size of Public Sub New(Name as String, Size as Long)". Two lines down I'm seeing errors when trying to reference the FileName and FileSize properties: "EnterpriseDT.Net.Ftp.FTPFile.fielName is not accessible in this context because it is 'Protected Friend'.

Guffa Over a year ago

@HK1: I corrected the syntax for the array. Regarding the properties from the items in the ftpfiles array, I just made a guess on what their names could be. I don't know what the items contain, so you have to substitute those names with the names of the properties that you want to use.

HK1 Over a year ago

Duh, that fixed all my errors. I'm surprised I didn't catch the second error there.

HK1 Over a year ago

Also, thanks for the note on Hungarian notation. I'm busy trying to sort through and unlearn a bunch of bad habits and practices that I developed while programming in MS Access.

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