VB.NET Core Classes in a Nutshell

Approaching the .NET FCL

It may seem that, given both the newness and the enormity of the .NET platform, a substantial learning curve is required to “learn” the .NET FCL. In fact, this isn’t the case; you can begin to take advantage of the class library immediately by selecting those classes, structures, and enumerations and their members that are of immediate interest to you and ignoring the rest. You can then gradually expand your familiarity with the .NET FCL as needed.

This incremental approach to learning the .NET FCL is possible because Visual Basic was written to run under the .NET platform, and much of the Visual Basic language (or at least the functions and procedures not implemented directly by the Visual Basic compiler) actually wrap functionality found in the .NET FCL.

The clearest example of this is to be found in the data types supported by Visual Basic. While Visual Basic’s data types appear to be intrinsic, in fact they are defined by the .NET FCL; Visual Basic merely provides wrappers for each of the .NET data types for which it offers native support. This, in fact, is one of the major strengths of the .NET Framework: it features the Common Type System (CTS), which allows components and applications written in one .NET-compliant language to more or less seamlessly interoperate with components written in other .NET-compliant languages. Table 1-1 shows the “intrinsic” Visual Basic data types and their corresponding .NET FCL data types.

Table 1-1. VB.NET data types and their corresponding .NET FCL data types

VB.NET data type	.NET FCL data type
Boolean	System.Boolean
Byte	System.Byte
Char	System.Char
Date	System.DateTime
Decimal	System.Decimal
Double	System.Double
Integer	System.Int32
Long	System.Int64
Object	System.Object
Short	System.Int16
Single	System.Single
String	System.String

That the standard VB data types are merely wrappers for CTS data types is indicated by the Visual Basic SystemTypeName function, which returns the name of a CTS data type that corresponds to a particular “intrinsic” VB data type. For example, the code fragment:

Dim i as Integer = 12345
Dim s As String = "New World"
  
Console.WriteLine(SystemTypeName(TypeName(i)))
Console.WriteLine(SystemTypeName(TypeName(s)))

shows that the VB Integer corresponds to the .NET System.Int32 data type, while the VB String data type corresponds to the .NET System.String data type. In other words, we could also declare and initialize our two variables as follows:

Dim i as System.Int32 = 12345
Dim s As System.String = "New World"

The fact that VB data types are really CTS data types means that we can access the fields, properties, and methods of CTS datatypes from VB variables. Consider, for example, the following code fragment:

Dim d As Double
Dim b As Byte
Dim s As String = InputBox("Enter a number (0-255): ")
  
If IsNumeric(s) Then
   d = CDbl(s)
   If b.MaxValue >= d And b.MinValue <= d Then
      b = CByte(s)
   End If
   Console.WriteLine(TypeName(b) & " value: " & b)
End If

The code simply checks whether the numeric equivalent of a string entered by the user is within the range of the VB Byte data type by retrieving the values of the System.Byte data type’s MinValue and MaxValue fields.

Tip

Because they don’t exist in the Framework Class Library, two intrinsic data types found in previous versions of VB have been removed from the language. The first is the Currency data type. In its place, use the Decimal data type, which in the .NET platform is a standard data type. (In previous versions of VB, the Decimal was a subtype of the Variant data type, and variables could be cast as decimals only by calling the CDec conversion function.) The second is the Variant data type, which has been replaced by the Object data type as VB’s “universal” data type.

Moreover, the reverse is also true: given a CTS data type, we can pass it as a parameter to methods that work on Visual Basic data types. For example:

Option Strict On
Imports Microsoft.VisualBasic
Imports System
  
Public Module modMain
  
Public Sub Main
   Dim iNum As Int32 = 1234
   Dim sNum As System.String = CStr(iNum)
  
   Console.WriteLine(Mid(sNum,3,2))
End Sub
  
End Module

This code includes two instances of calls to VB.NET methods using CTS data types. The first is the call to the CStr conversion function, which is passed a variable of type Int32. The second is the call to the Mid string manipulation function, which is passed a variable of type System.String.

This means that, when working with Visual Basic data types, you can continue to call intrinsic Visual Basic functions, and call the members of .NET data types when they provide important functionality not available directly from Visual Basic. The following sections detail some of those functions.

Array Class

Just as Visual Basic scalar data types are in fact CTS scalar data types, so Visual Basic arrays are actually members of the .NET System.Array class. Some of its members that are not readily available in Visual Basic .NET are shown in the following table:

Name	Member type	Description
BinarySearch	Shared method	Searches a one-dimensional array for a particular value
Clear	Shared method	Sets a range of array elements to zero, False, or a null reference, depending on the members’ data type
Copy	Shared method	Copies a portion of one array to another and performs any necessary type conversions
CopyTo	Method	Copies all the elements of a one-dimensional array to another one-dimensional array starting at a particular index position
IndexOf	Shared method	Returns the index of the first occurrence of a particular value in an array
IsFixedSize	Property	Returns a Boolean indicating whether an Array object has a fixed size
IsReadOnly	Property	Returns a Boolean indicating whether the elements in Array object are read-only
LastIndexOf	Shared method	Returns the index of the last occurrence of a particular value in an array
Rank	Property	Returns an Integer indicating the number of dimensions of the array
Reverse	Shared method	Reverses the elements in all or part of a one-dimensional array
Sort	Shared method	Sorts a one-dimensional array

Boolean Structure

The following table lists the members of the System.Boolean structure that are not readily available in the Visual Basic .NET language:

Name	Member type	Description
FalseString	Shared field	Returns the string representation of the Boolean value False. This is a read-only constant value.
Parse	Shared method	Converts a string (whose value must be either Boolean.TrueString or Boolean.FalseString) to its Boolean equivalent.
TrueString	Shared field	Returns the string representation of the Boolean value True. This is a read-only constant value.

Byte Structure

The Visual Basic .NET Byte data type is synonymous with the .NET System.Byte data type. The following table lists some of the members of the Byte class that are not readily available in Visual Basic:

Name	Member type	Description
MaxValue	Shared field	A constant representing the largest possible value of an instance of the Byte class
MinValue	Shared field	A constant representing the smallest possible value of an instance of the Byte class
Parse	Shared method	Converts the numeric representation of a string to its Byte equivalent

Char Structure

Char, a new data type in VB.NET, corresponds to the System.Char data type. Some of the members of the latter that offer functionality not available in VB.NET are shown in the following table:

Name	Member type	Description
GetUnicodeCategory	Shared method	Returns a member of the UnicodeCategory enumeration (in the System.Globalization namespace) indicating the character type of a Char object.
IsControl	Shared method	Returns a Boolean indicating whether a particular Unicode character is a control character.
IsDigit	Shared method	Returns a Boolean indicating whether a particular Unicode character is a decimal digit. (The decimal and thousands separators are not considered digits.)
IsLetter	Shared method	Returns a Boolean indicating whether a particular Unicode character is a letter of the alphabet.
IsLetterOrDigit	Shared method	Returns a Boolean indicating whether a particular Unicode character is a digit or a letter of the alphabet.
IsLower	Shared method	Returns a Boolean indicating whether a particular Unicode character is a lowercase letter. The method returns True only for letters of the alphabet; that is, Char.IsLetter must also return True.
IsNumber	Shared method	Returns a Boolean indicating whether a particular Unicode character is a decimal or hexadecimal digit.
IsPunctuation	Shared method	Returns a Boolean indicating whether a particular Unicode character is a punctuation mark.
IsSeparator	Shared method	Returns a Boolean indicating whether a particular Unicode character is a separator character (e.g., a space). The method does not return True if the character is a numeric separator.
IsSymbol	Shared method	Returns a Boolean indicating whether a particular Unicode character is a symbol.
IsUpper	Shared method	Returns a Boolean indicating whether a particular Unicode character is an uppercase letter. The method returns True only for letters of the alphabet; that is, Char.IsLetter must also return True.
IsWhiteSpace	Shared method	Returns a Boolean indicating whether a particular Unicode character is white space.
MaxValue	Shared field	A constant containing the largest possible value of Char object.
MinValue	Shared field	A constant containing the smallest possible value of a Char object.
Parse	Shared method	Converts a particular character in a string to a Char object.

DateTime Structure

The Visual Basic Date data type corresponds to the .NET Framework’s DateTime structure. The following table lists the DateTime members whose functionality is not available in the date/time functions supported by the VB.NET language:

Name	Member type	Description
AddMilliseconds	Method	Adds a designated number of milliseconds to the DateTime instance
AddTicks	Method	Adds a designated number of ticks to the DateTime instance
CompareTo	Method	Compares the current DateTime instance to an object and returns an indication of their relative values
DaysInMonth	Shared method	Returns the number of days in a designated month and year
FromOADate	Shared method	Converts an OLE Automation Date value to a DateTime instance
GetDateTimeFormats	Method	Returns a String array containing all the string representations supported by the standard DateTime format specifiers
IsLeapYear	Shared method	Returns a Boolean indicating whether a particular year is a leap year
MaxValue	Shared field	A constant containing the largest possible value of a DateTime instance
Millisecond	Property	Retrieves the milliseconds component of a DateTime instance
MinValue	Shared field	A constant containing the smallest possible value of a DateTime instance
Now	Shared property	Returns the current local date and time
Parse	Shared method	Converts a string representation of a date/time to a DateTime instance
ParseExact	Shared method	Converts a string representation of a date/time in a specified format to its DateTime equivalent
Ticks	Property	Returns a Long containing the number of ticks that represent the date and time value of this instance
TimeOfDay	Property	Returns the current time of day
Today	Shared property	Returns the current date
ToFileTime	Method	Converts the DateTime instance to the format of the local system’s file time
ToLocalTime	Method	Converts the current coordinated universal time (UTC) to local time
ToLongDateString	Method	Converts a DateTime instance to its long date string representation
ToLongTimeString	Method	Converts a DateTime instance to its long time string representation
ToOADate	Method	Converts the value of this instance to a Double representing the OLE Automation date
ToShortDateString	Method	Converts a DateTime instance to its short date string representation
ToShortTimeString	Method	Converts a DateTime instance to its short time string representation
ToUniversalTime	Method	Converts the value of the DateTime instance to coordinated universal time (UTC)
UtcNow	Shared property	Returns a DateTime instance that represents the current local date and time expressed as the coordinated universal time (UTC)

Decimal Structure

The VB.NET Decimal data type corresponds directly to the System.Decimal structure. The CTS Decimal structure includes the following members whose functionality is not readily available in VB.NET:

Name	Member type	Description
FromOACurrency	Shared method	Converts a Long containing an OLE Automation Currency value (e.g., a VB6 or VBScript Currency value) to a Decimal value
GetBits	Shared method	Converts a particular Decimal value to its binary representation and returns that value as an Integer
MaxValue	Shared field	A constant containing the largest possible value of a Decimal object
MinValue	Shared field	A constant containing the smallest possible value of a Decimal object
ToOACurrency	Shared method	Converts a Decimal value to an OLE Automation Currency value (e.g., a VB6 or VBScript Currency value), which it returns as a Long

Double Structure

The VB.NET Double data type corresponds to the .NET Framework’s System.Double data type. The following table lists the members of the latter that offer functionality not found in the Visual Basic .NET language:

Name	Member type	Description
Epsilon	Shared field	A constant containing the smallest positive Double value greater than zero
MaxValue	Shared field	A constant containing the largest possible value of a Double object
MinValue	Shared field	A constant containing the smallest possible value of a Double object
NaN	Shared field	A constant containing the representation of a value that is not a number (NaN)
NegativeInfinity	Shared field	A constant containing a number that represents negative infinity
PositiveInfinity	Shared field	A constant containing a number that represents positive infinity
IsInfinity	Shared method	Returns a Boolean indicating whether the value of a Double object represents positive or negative infinity
InNaN	Shared method	Returns a Boolean indicating whether a Double object contains a value that is not a number (NaN)
IsNegativeInfinity	Shared method	Returns a Boolean indicating whether the value of a Double object represents negative infinity
IsPositiveInfinity	Shared method	Returns a Boolean indicating whether the value of a Double object represents positive infinity
Parse	Shared method	Converts the string representation of a number to its Double equivalent

Int16 Structure

The VB.NET Short data type corresponds directly to the System.Int16 structure. The members of the latter structure that offer unique functionality are shown in the following table:

Name	Member type	Description
MaxValue	Shared field	A constant containing the largest possible value of an Int16 object
MinValue	Shared field	A constant containing the smallest possible value of an Int16 object
Parse	Shared method	Converts the string representation of a number to its Int16 equivalent

Int32 Structure

The VB.NET Integer data type corresponds directly to the System.Int32 structure. The members of the Int32 structure that offer unique functionality are shown in the following table:

Name	Member type	Description
MaxValue	Shared field	A constant containing the largest possible value of an Int32 object
MinValue	Shared field	A constant containing the smallest possible value of an Int32 object
Parse	Shared method	Converts the string representation of a number to its Int32 equivalent

Int64 Structure

The VB.NET Long data type corresponds directly to the System.Int64 structure. The members of the Int64 structure that offer unique functionality are shown in the following table:

Name	Member type	Description
MaxValue	Shared field	A constant containing the largest possible value of an Int64 object
MinValue	Shared field	A constant containing the smallest possible value of an Int64 object
Parse	Shared method	Converts the string representation of a number to its Int64 equivalent

Object Class

The VB.NET Object data type corresponds to the System.Object class. System.Object, however, offers no functionality that is not available through the standard Visual Basic language.

Single Structure

The VB.NET Single data type corresponds to the .NET Framework’s System.Single data type. The following table lists the members of the latter that offer functionality not found in the Visual Basic .NET language:

Name	Member type	Description
Epsilon	Shared field	A constant containing the smallest positive Single value greater than zero
MaxValue	Shared field	A constant containing the largest possible value of a Single object
MinValue	Shared field	A constant containing the smallest possible value of a Single object
NaN	Shared field	A constant containing the representation of a value that is not a number (NaN)
NegativeInfinity	Shared field	A constant containing a number that represents negative infinity
PositiveInfinity	Shared field	A constant containing a number that represents positive infinity
IsInfinity	Shared method	Returns a Boolean indicating whether the value of a Single object represents positive or negative infinity
InNaN	Shared method	Returns a Boolean indicating whether a Single object contains a value that is not a number (NaN)
IsNegativeInfinity	Shared method	Returns a Boolean indicating whether the value of a Single object represents negative infinity
IsPositiveInfinity	Shared method	Returns a Boolean indicating whether the value of a Single object represents positive infinity
Parse	Shared method	Converts the string representation of a number to its Single equivalent

String Class

The VB.NET String data type is equivalent to the System.String class. The members of the String class that offer functionality not incorporated in the VB.NET language are shown in the following table:

Name	Member type	Description
Chars	Property	Returns a Char instance representing the character at a particular position in a string
Clone	Method	Returns an additional reference to a particular String instance
CompareOrdinal	Shared method	Compares two strings without considering locale settings
CopyTo	Method	Copies a designated number of characters starting at a particular position in a string to a character array
Empty	Shared field	A constant representing an empty string
EndsWith	Method	Returns a Boolean indicating whether the String instance ends with the substring passed to the method as an argument
Format	Shared method	Replaces each format specification in a string with its corresponding value
IndexOf	Method	Returns the position of the first occurrence of a character or a substring within the string instance
IndexOfAny	Method	Returns the index of the first occurrence in this String instance of any element in a character array
Insert	Method	Inserts a substring at a designated position of a String instance
LastIndexOf	Method	Returns the position of the last occurrence of a designated character or substring within the string instance
LastIndexOfAny	Method	Returns the position of the last occurrence in this String instance of any of a set of characters in a character array
PadLeft	Method	Right aligns the characters in a String instance by padding them with a space or another designated character
PadRight	Method	Left aligns the characters in a String instance by padding them with a space or another designated character
Remove	Method	Deletes a specified number of characters from a String instance beginning at a designated position
StartsWith	Method	Returns a Boolean indicating whether the String instance begins with a designated substring or character
ToCharArray	Method	Copies the characters in the String instance to a Unicode character array

Non-CTS Data Types

Note, however, that because they are not part of the Common Language Specification (the specification that defines the core functionality that a .NET platform must implement), VB does not wrap the following CTS data types:

System.SByte

Description: Signed byte

Value Range: -128 to 127

System.UInt16

Description: Unsigned 16-bit integer

Value Range: 0 to 65,535

System.UInt32

Description: Unsigned 32-bit integer

Value Range: 0 to 4,294,967,295

System.UInt64

Description: Unsigned 64-bit integer

Value Range: 0 to 18,446,744,073,709,551,615