Casting in .NET

13. September 2007 04:20 by Mrojas in General  //  Tags: , , ,   //   Comments (0)

.NET has a more strict typing than VB6
So you must check in some circumstances if your object implements an interface or not.

So I had used the as and is operators in C# but I did not know how to do that.
I did I little research and I discovered some things about casting operators for VB.NET

 

Operator Example Observations
CType Dim testNumber As Long = 1000
' The following line of code sets testNewType to 1000.0.
Dim testNewType As Single = CType(testNumber, Single)
 		 Throws InvalidCastException or OverflowException

It could be less eficient due to VB.Net helper routines.

This is a Narrowing and Widening operator.

It can be overloaded

Public Structure digit
Private dig As Byte
    Public Sub New(ByVal b As Byte)
        If (b OrElse b > 9) Then Throw New _
            System.ArgumentException("Argument outside range for Byte")
        Me.dig = b
    End Sub
    Public Shared Widening Operator CType(ByVal d As digit) As Byte
        Return d.dig
    End Operator
    Public Shared Narrowing Operator CType(ByVal b As Byte) As digit
        Return New digit(b)
    End Operator
End Structure
 

 
DirectCast Dim f As New System.Windows.Forms.Form
Dim c As System.Windows.Forms.Control
' The following conversion succeeds.
c = DirectCast(f, System.Windows.Forms.Control)
 		 Throws InvalidCastException. Is more efficient than CType because it does not depend on the Visual Basic helper runtime functions. It can even detect some errors as invalid casts during compile time
 

However it requires a relationship of inheritance of implementation
For example:

Dim q As Object = 2.37
Dim i As Integer = CType(q, Integer)
' The following conversion fails at run time
Dim j As Integer = DirectCast(q, Integer)
 

The run-time type of q is Double. CType succeeds because Double can be converted to Integer. However, the first DirectCast fails at run time because the run-time type of Double has no inheritance relationship with Integer, even though a conversion exists
 
TryCast     Dim obj As MyType = TryCast(obj, MyType)
    If obj Is Nothing Then
      ' Object could not be cast
   Else
     ' Object was casted
   End If		 Throws no exceptions.


All this information has been taken from the MSDN site. This is just a quick summary. For more information see:

Type Conversion Functions
Conversion Functions (Visual Basic)

Widening and Narrowing Conversions
Implicit and Explicit Conversions
 

Fixed Len Strings in Visual Basic

7. September 2007 09:34 by Mrojas in General  //  Tags: , , ,   //   Comments (0)

This is a nostalgic note. Someone asked me, "hey, how do you make a fixed len string in VB6?"
As the computer geek that I am, that the kind of questions I like to be able to answer.
These are important questions like all those questions from the 80's rally:

The name of all the original thundercats...
The planet where Luck Skywalker went to learn with Yoda...
Which Star Trek character appear in ALL the episodes (yes it is Spock, Kirk is not in all of them)
Well, the thing is to define a fixed len string in VB6 you do something like:


Dim aString As String * 10
If you do something like:

aString = "Mau" ' aString ==> "Mau "
That's all

Fixed length strings are automatically filled with spaces to pad them to their fixed-length. How do you get rid of the extra spaces? Duh!!! with RTrim$ don't you remember

When a variable like aString is declared, it will be filled with Null characters until it is used.

And yes functions (RTrim$, LTrim$, and Mid$) will not trim Null characters, so be sure to assign it with an empty string "" immediately.


Ahh! and by the way when you translate that to .NET, .NET does not have a fixed len string so the easiest thing to do is use:
Microsoft.VisualBasic.Compatibility.VB6.FixedLengthString.

[C#]

using Microsoft.VisualBasic.Compatibility;
...

void foo()

{

VB6.FixedLengthString aString = VB6.FixedLengthString(10, "Mau");

}

 

Migration of VB6 POS

7. May 2007 08:46 by Mrojas in General  //  Tags: , , , , , ,   //   Comments (0)

POS (Point of Sale) software is everywhere. Whether you're at a Bar, at Denny's, Pizza Hut, BK or at the Duty Free. It is maybe one of the software's more commonly used. A POS system is generally simple. It manages a basic inventory, registers sales, and somethings manages credit card payments. Obviously there are far more complex POS systems. A lot of POS systems where programmed in VB6. But as you know VB6 language (and I'm not discussing the reasons here) is now a dead language. A lot of customers do not want to buy VB6 applications, even if they get the job done. So it's time to move on. This is the First of a series of posts around issues migrating VB6 POS applications. If you have any comments just send them now!

Something like sprintf in C# or VB.NET

31. July 2006 11:11 by Mrojas in General  //  Tags: , , ,   //   Comments (0)

Recently I was wondering how to format  an output string like I used in C or C++ where we had the infamous and powerful sprintf but I could not find a good refence until I found this page.

http://blog.stevex.net/index.php/string-formatting-in-csharp/ I think it will be very useful to print it and have it close as a good cheat code sheet.

 

More Color to your Traces!

29. May 2006 08:37 by Mrojas in General  //  Tags: , ,   //   Comments (0)

Most Visual Basic programmers are familiar with using Debug.Print to follow their code's execution. The .NET environment introduces Tracing falicities that allows you to send messages to files or the console.

However the console output could be improved by using colors to highlight certain events. 
I developed a simple ColorTraceListener that can be used either with the My.Application.Log object or the Trace.TraceXXX methods. 
I first thing to do is create a ClassLibrary. It will be called ColorTraceListener. Add a ColorTraceListener.cs File and fill it with the following code: 

Imports System

Imports System.Diagnostics

Imports System.Globalization

Imports System.Text

Imports System.Runtime.InteropServices 

Public Class ColorTraceListener

    Inherits ConsoleTraceListener

    Public Sub New()

        MyBase.New()

    End Sub 

    Public Sub New(ByVal useErrorStream As Boolean)

        MyBase.New(useErrorStream)

    End Sub 

    Friend Function IsEnabled(ByVal opts As TraceOptions) As Boolean

        Return ((opts And Me.TraceOutputOptions) <> TraceOptions.None)

    End Function 
 
 

    False)> _

    Public Overrides Sub TraceData(ByVal eventCache As TraceEventCache, ByVal source As String, ByVal eventType As TraceEventType, ByVal id As Integer, ByVal data As Object)

        If ((Me.Filter Is Nothing) OrElse Me.Filter.ShouldTrace(eventCache, source, eventType, id, Nothing, Nothing, Nothing, data)) Then

            Me.WriteHeader(source, eventType, id)

            Dim text1 As String = String.Empty

            If (Not data Is Nothing) Then

                text1 = data.ToString

            End If

            Me.WriteLine(text1)

            Me.WriteFooter(eventCache)

        End If

    End Sub 

    False)> _

    Public Overrides Sub TraceData(ByVal eventCache As TraceEventCache, ByVal source As String, ByVal eventType As TraceEventType, ByVal id As Integer, ByVal ParamArray data As Object())

        If ((Me.Filter Is Nothing) OrElse Me.Filter.ShouldTrace(eventCache, source, eventType, id, Nothing, Nothing, Nothing, data)) Then

            Me.WriteHeader(source, eventType, id)

            Dim builder1 As New StringBuilder

            If (Not data Is Nothing) Then

                Dim num1 As Integer = 0

                Do While (num1 < data.Length)

                    If (num1 <> 0) Then

                        builder1.Append(", ")

                    End If

                    If (Not data(num1) Is Nothing) Then

                        builder1.Append(data(num1).ToString)

                    End If

                    num1 += 1

                Loop

            End If

            Me.WriteLine(builder1.ToString)

            Me.WriteFooter(eventCache)

        End If

    End Sub 
 

    False)> _

    Public Overrides Sub TraceEvent(ByVal eventCache As TraceEventCache, ByVal source As String, ByVal eventType As TraceEventType, ByVal id As Integer, ByVal message As String)

        If ((Me.Filter Is Nothing) OrElse Me.Filter.ShouldTrace(eventCache, source, eventType, id, message, Nothing, Nothing, Nothing)) Then

            Me.WriteHeader(source, eventType, id)

            Me.WriteLine(message)

            Me.WriteFooter(eventCache)

        End If

    End Sub 
 

    False)> _

    Public Overrides Sub TraceEvent(ByVal eventCache As TraceEventCache, ByVal source As String, ByVal eventType As TraceEventType, ByVal id As Integer, ByVal format As String, ByVal ParamArray args As Object())

        If ((Me.Filter Is Nothing) OrElse Me.Filter.ShouldTrace(eventCache, source, eventType, id, format, args, Nothing, Nothing)) Then

            Me.WriteHeader(source, eventType, id)

            If (Not args Is Nothing) Then

                Me.WriteLine(String.Format(CultureInfo.InvariantCulture, format, args))

            Else

                Me.WriteLine(format)

            End If

            Me.WriteFooter(eventCache)

        End If

    End Sub 
 
 
 
 

    Private Sub WriteFooter(ByVal eventCache As TraceEventCache)

        If (Not eventCache Is Nothing) Then

            Me.IndentLevel += 1

            If Me.IsEnabled(TraceOptions.ProcessId) Then

                Me.WriteLine(("ProcessId=" & eventCache.ProcessId))

            End If

            If Me.IsEnabled(TraceOptions.LogicalOperationStack) Then

                Me.Write("LogicalOperationStack=")

                Dim stack1 As Stack = eventCache.LogicalOperationStack

                Dim flag1 As Boolean = True

                Dim obj1 As Object

                For Each obj1 In stack1

                    If Not flag1 Then

                        Me.Write(", ")

                    Else

                        flag1 = False

                    End If

                    Me.Write(obj1.ToString)

                Next

                Me.WriteLine(String.Empty)

            End If

            If Me.IsEnabled(TraceOptions.ThreadId) Then

                Me.WriteLine(("ThreadId=" & eventCache.ThreadId))

            End If

            If Me.IsEnabled(TraceOptions.DateTime) Then

                Me.WriteLine(("DateTime=" & eventCache.DateTime.ToString("o", CultureInfo.InvariantCulture)))

            End If

            If Me.IsEnabled(TraceOptions.Timestamp) Then

                Me.WriteLine(("Timestamp=" & eventCache.Timestamp))

            End If

            If Me.IsEnabled(TraceOptions.Callstack) Then

                Me.WriteLine(("Callstack=" & eventCache.Callstack))

            End If

            Me.IndentLevel -= 1

        End If

    End Sub 

    Private Sub WriteHeader(ByVal source As String, ByVal eventType As TraceEventType, ByVal id As Integer)

        Dim oldColor As ConsoleColor = Console.ForegroundColor

        Select Case eventType

            Case TraceEventType.Error

                Console.ForegroundColor = ConsoleColor.Red

            Case TraceEventType.Critical

                Console.ForegroundColor = ConsoleColor.Magenta

            Case TraceEventType.Information

                Console.ForegroundColor = ConsoleColor.White

                'Case TraceEventType.Resume

                'Case TraceEventType.Start

                'Case TraceEventType.Suspend

                'Case(TraceEventType.Transfer)

                'Case TraceEventType.Verbose

            Case TraceEventType.Warning

                Console.ForegroundColor = ConsoleColor.Yellow

        End Select

        Me.Write(String.Format(CultureInfo.InvariantCulture, "{0} {1}:", New Object() {source, eventType.ToString}))

        Console.ForegroundColor = oldColor

        Me.Write(String.Format(CultureInfo.InvariantCulture, " {0} : ", New Object() {id.ToString(CultureInfo.InvariantCulture)}))

    End Sub

End Class 

The methods that handle the headers in the TextWriteListener are private (WriteHeader and WriterFooter) so we need to override them. Reflector comes very handy in this cases. 

No to test it Create a Vb Console Application: 

Module Module1 

    Sub Main() 
 

        My.Application.Log.WriteEntry("Error!", TraceEventType.Error)

        My.Application.Log.WriteEntry("Warning", TraceEventType.Warning)

        My.Application.Log.WriteEntry("Info", TraceEventType.Information)

        My.Application.Log.WriteEntry("Info", TraceEventType.Critical) 

        Trace.TraceError("An Error Happened!")

        Trace.TraceInformation("Just letting you know!")

        Trace.TraceWarning("Watch the road ahead") 

    End Sub 

End Module 

And use a simple configuration file like the following: 

xml version="1.0" encoding="utf-8" ?>

<configuration>

    <system.diagnostics>

      <trace autoflush="true">

        <listeners>

          <add name="ColorLog" />

        listeners>

      trace>

        <sources>

            This section defines the logging configuration for My.Application.Log -->

            <source name="DefaultSource" switchName="DefaultSwitch">

                <listeners>

                    <add name="ColorLog"/>

                listeners>

            source>

        sources>

        <switches>

            <add name="DefaultSwitch" value="Verbose" />

        switches>

       <sharedListeners>

          <add name="ColorLog" type="Mrojas.ColorTraceListener, ColorTraceListener" />

        sharedListeners>

    system.diagnostics>

configuration>