If they all have the same properties, I would suggest an abstract base or an
interface that defines all of the properties, then concrete implementations
of each of them. I think using a case statement to determine type, the way
you are, might be an indication you need to look at abstraction:
Class MustInherit PhoneBook
Public MustOverride ReadOnly Property Name as String
End Class
Class PhoneBookFormatXYZ
Inherits PhoneBook
Public Overrides ReadOnly Property Name as String
return mid(_LineOfText, 1, 12)
End Property
End Class
Or for an interface:
Interface IPhoneBook
ReadOnly Property Name as String
End Interface
Class PhoneBookFormatXYZ
Implements IPhoneBook
Public ReadOnly Property Name as String Implements IPhoneBook.Name
return mid(_LineOfText, 1, 12)
End Property
End Class
I'd prefer the interface version in this case because it doesn't limit you
to a singly rooted hierarchy.
Then when you want to use it, you can do something like:
Dim pb1 as IPhoneBook
Dim pb2 as IPhoneBook
Dim pb3 as IPhoneBook
Dim pb4 as IPhoneBook
pb1 = New PhoneBookFormatXYZ ' implicit cast
since pb1 XYZ implements IPhoneBook
pb2 = New PhoneBookFormatZZABC
pb3 = New PhoneBookFormatABC
pb4 = New PhoneBookFormat123
Dim s as string
s = pb1.Name ' compiler knows
about Name property since all pbX objects are IPhoneBooks
...
s = pb2.Name
...
s = pb3.Name
...
s = pb4.Name
...
-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Jon Rothlander
Sent: Saturday, September 09, 2006 12:38 AM
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: Re: [ADVANCED-DOTNET] Need help with a simple VB.Net Problem
Thanks for you reply. Let me try to explain what I am trying to do so you
can understand what I need to do. The sample I set up shows the problem,
but it doesn't really show you what I am trying to do. Maybe I'm looking at
the wrong solution to begin with.
What I have is a class library that handles formatting for me from
fixed-format text files. Let's say that I have the following line in a
file.
Phonebook Format 1
Greg Rothlander 1234 First Street Austin Texas
12345
Jerry Lee 5678 3rd Street Dallas Texas
34567
Phonebook Format 2
Greg Rothlander 1234 First Street Austin Texas
12345
Jerry Lee 5678 3rd Street Dallas Texas
34567
Phonebook Format 3
Greg Rothlander 1234 First Street Austin,Texas 12345
Jerry Lee 5678 3rd Street Dallas,Texas
34567
So in the first type of file and the class that defines the character
positions, the first name is character position 1 thru 12, then last name is
13 thru 25, etc. What I did was build a class structure over the class.
Lets say each of the phonebook class below is wrapped into a single
PhonebookFormats Class. Sort of like... (This is not working code. Just
enough to explain what I am doing.)
Class PhonebookFormats
Class Phonebook1
Class EntryItem
_Lineoftext as string = ""
Property FirstName() as string
return mid(_LineOfText, 1, 12)
End Property
End Class
Class PhoneBook1
However, depending on the file being read, other classes might look like the
following.... Keep in mind that in the real class there are about 50
properties like the Name property here. The property simple pulls a given
character set from the LineOfText property.
Class Phonebook2
Class EntryItem
_Lineoftext as string = ""
Property Name() as string
return mid(_LineOfText, 1, 18)
End Property
End Class
End Class
Class Phonebook3
Class EntryItem
_Lineoftext as string = ""
Property Name() as string
return mid(_LineOfText, 1, 25)
End Property
End Class
End Class 'Phonebook3
End Class 'PhonebookFormats
One thing to keep in mind is that the class might have sub-class like the
following... Lets say that there might be 3 different types of address
records in each phonebook entry. The good thing is that if one of the
Phonebooks has three address formats, they all will. That might look
like...
Class Phonebook3
Class EntryItem
Private _Lineoftext as string = ""
Public Property LineofText
Set (Value as string)
_LineOfText = Value
End Set
End Property
Property Name() as string
return mid(_LineOfText, 1, 25)
End Property
Property Address() as string
return mid(_LineOfText, 30, 25)
End Property
Class AddressFormat1
property number...
property street...
End Class
Class AddressFormat2
property number...
property street...
End Class
Class AddressFormat3
property number...
property street...
End Class
End Class
Class PhoneBook3
So what I need to be able to do is create the classes for each type of
record, which is actually many... probably 50 to 60 different types. Then
based on what type of file I read, I need to load the correct class that
contains the file formats. The code that processes the class and data after
it is loaded, is the same for ALL of the code. It might have code like the
following, assuming that the object version of this was working...
Dim obj as object
Select Case WhateverClassIsNeeded
Case 0
obj = new PhonebookFormats.Phonebook1
Case 1
obj = new PhonebookFormats.Phonebook2
Case 2
obj = new PhonebookFormats.Phonebook3
End Select
Dim sName as string = Obj.EntryItem.Name
Dim sAddress as string = Obj.EntryItem.Address
Does that make any sense? I have all of these classes where are basically
the same thing with different formats. They have pretty much the same
properties, but each property has a unique definition do to the character
position it is looking at for the given text file.
I have set up something similar using reflection, but I was hoping that
there was a better way.
There may be a better way to design this. If so, I would be very interested
to here what others think.
Best regards,
Greg
-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Bob Provencher
Sent: Friday, September 08, 2006 8:22 PM
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: Re: [ADVANCED-DOTNET] Need help with a simple VB.Net Problem
I'm more familiar with C#, but I'll take a stab at it.
I think Test1 is attempting to create new Object and store it's reference in
obj, then create a new dateformatter and overwrite the ref previously stored
in obj. This is not a cast. The type of obj is still Object. I think you
can just do:
Dim obj as Object
obj = New DateFormatter.YearFormatter
In Test2, you are dimensioning the same var twice. I think what you want
is:
'Test2
'Dim obj As New DateFormatter.YearFormatter
'Lets just pretend that there is logic that could cause either one
to be hit.
'For this sample, I'm forcing it to the first case.
Dim int As Integer = 0
Dim str as String
Select Case int
Case 0
str = obj.PreY2K.YY
Case 1
str = obj.PostY2K.YYYY
End Select
But, your code does not know that your object has PreY2K and PostY2K
properties since you only have an Object reference. Since you only have the
one type you can just change the declaration to be that type:
Dim dtFmter as DateFormatter.YearFormatter
If you have more than one time and that is the reason you think you need to
Dim as an Object, then you might need to introduce a class hierarchy or an
interface. Give us more details on what you are trying to do.
-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Jon Rothlander
Sent: Friday, September 08, 2006 10:06 PM
To: ADVANCED-DOTNET@DISCUSS.DEVELOP.COM
Subject: [ADVANCED-DOTNET] Need help with a simple VB.Net Problem
I'm hoping that someone can take a few minutes and take a look at the
following code for me. It may look complex at first, but it actually is
very simple. What I have here is a VB.Net WinForm with no controls on the
form. When it executes, it runs through a sample app that I set up that
recreates the problem that I am having, but it's not the same application.
I wrote a sample that is based on a Y2K sample that I just made up because
what I am actually working on is a compiler and there's just too much in the
code to post the real thing. So this sample recreates the same problem, but
keep in mind that it's not the same code so my solutions may be limited.
If you create a WinForm and paste the code and close at the bottom of this
post, you will see the following in a Test() function at the bottom of the
code...
'Test1
Dim obj As New Object
obj = New DateFormatter.YearFormatter
'Test2
'Dim obj As New DateFormatter.YearFormatter
'Lets just pretend that there is logic that could cause either one
to be hit.
'For this sample, I'm forcing it to the first case.
Dim int As Integer = 0
Select Case int
Case 0
Dim str As String = obj.PreY2K.YY
Case 1
Dim str As String = obj.PostY2K.YYYY
End Select
To see what my problem is. Use the code below and execute with a breakpoint
on the line after the Test1 comment. You will get an error on the "dim str"
line. Then comment out the Test1 code and uncomment the Test2 code. Run it
again and note that you do not get the error. What's the difference?
Note that Test1 uses a generic object and then casts it as the YearFormatter
class. This causes an error when it hits the code that looks at the
PreY2K.YY property. However in Test2 if I just go ahead and create it obj
as that type, then I do not get an error. I do not see what the difference
between the two is, but apparently I am overlooking something significant.
The problem is that I have been using logic like Test2 and I need to change
it to Test1 using a generic object. I need to make it generic because I
have a number of different class that would be equivalent to YearFormatter.
Maybe it would be sort of like having YearFormmater, YearFormatterY2K, and
YearFormatterPreY2K classes, then needed the logic of the code to pick which
one to use. So I need to be able to control which class becomes the obj
object and set it accordingly.
In the end, I just need to figure out how to get Test1 to work like Test2.
Any ideas? Any suggestions or ideas would be very much appreciated. I
think I am over looking something simple here.
My sample code is below.
Best regards,
Greg Rothlander
Public Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
Public Sub New()
MyBase.New()
'This call is required by the Windows Form Designer.
InitializeComponent()
'Add any initialization after the InitializeComponent() call
End Sub
'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub
'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer
'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
<System.Diagnostics.DebuggerStepThrough()> Private Sub
InitializeComponent()
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 273)
Me.Name = "Form1"
Me.Text = "Form1"
End Sub
#End Region
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim obj As New SomeClass
obj.Test()
End Sub
End Class
Class DateFormatter
Class YearFormatter
Class PreY2K
' Definition for pre y2k file.
' YY
Private Shared _YY As String = ""
Public Shared Property YY() As String
Get
Return _YY
End Get
Set(ByVal Value As String)
_YY = Value
End Set
End Property
Public Shared Function ConvertToY2K() As String
If CInt(YY > 50) Then
Return "19" & YY
Else
Return "20" & YY
End If
End Function
End Class
Class PostY2K
' Definition for post y2k file.
' YYYY
Private Shared _YYYY As String = ""
Public Shared Property YYYY() As String
Get
Return _YYYY
End Get
Set(ByVal Value As String)
_YYYY = Value
End Set
End Property
Public Shared Function ConvertToPreY2K() As String
Return Mid(YYYY, 3, 2)
End Function
End Class
End Class
End Class
Class SomeClass
Public Function Test() As String
'Test1
Dim obj As New Object
obj = New DateFormatter.YearFormatter
'Test2
'Dim obj As New DateFormatter.YearFormatter
Dim int As Integer = 0
Select Case int
Case 0
Dim str As String = obj.PreY2K.YY
Case 1
Dim str As String = obj.PostY2K.YYYY
End Select
End Function
End Class
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