22.5 Class, Structure, and Interface Members

Classes, structures, and interfaces can contain one or more fields, methods, properties, and events. This section will discuss converting the C# syntax for each of these constructs to VB.

Note that .NET supports both static (or shared) members (which apply to the type as a whole, and typically do not require that an object of that type be instantiated) and instance members (which apply only to an instance of that type). Shared or static members are indicated by using the static keyword in C#. For example:

public static bool IsMnemonic(char charCode, string text);

The corresponding VB keyword is Shared. Hence, the FromResource method, when converted to VB, has the following syntax:

Public Shared Function IsMnemonic(charCode As Char, text As String) _
   As Boolean

22.5.1 Fields

A field is simply a constant or a variable that is exposed as a publicly accessible member of a type. In C#, for example, the Nowhere field of the DataGrid.HitTestInfo class has the syntax:

public static readonly DataGrid.HitTestInfo Nowhere;

Note that C# indicates the data type of a field before the name of the field. (For C# data types and their VB equivalents, see Table 22-3.) Also note that fields are most often read-only. Constant fields, in fact, are always read-only. As a result, the use of the C# readonly keyword and the VB ReadOnly keyword with fields is quite common.

The syntax for the Nowhere field in Visual Basic then becomes:

Public Shared ReadOnly Nowhere As DataGrid.HitTestInfo

22.5.2 Methods

In C#, all methods have a return value, which appears before the name of the function; in contrast, VB differentiates between function and subprocedures. C# functions without an explicit return value return void. For example, one of the overloads of the Bitmap class's MakeTransparent method has the following syntax in C#:

public void MakeTransparent( );

C# methods that return void are expressed as subprocedures in VB. So the corresponding syntax of the MakeTransparent method is:

Public Sub MakeTransparent( )

All C# methods other than those returning void are functions in VB. The function's return value follows appears in an As clause at the end of the function declaration. C# data types and their VB equivalents are shown in Table 22-3. Methods that return arrays are indicated by adding braces ([ ]) to the return data type in C# and parentheses (( ))to the return data type in VB.

For example, the Focus method of the Control class has the C# syntax:

public bool Focus( );

The VB equivalent is:

Public Function Focus( ) As Boolean

Table 22-3. C# data types and their VB equivalents

C# data type	VB data type
bool	Boolean
byte	Byte
char	Char
decimal	Decimal
double	Double
float	Single
int	Integer
long	Long
object	Object
sbyte	System.SByte
short	Short
string	String
System.Currency	Currency
System.DateTime	Date
uint	System.UInt32
ulong	System.UInt64
ushort	System.UInt16
<class_name>	<class_name>
<delegate_name>	<delegate_name>
<interface_name>	<interface_name>
<structure_name>	<structure_name>

Method parameters in C# take the general form:

<data_type> <parameter_name>

In VB, method parameters take the form:

<parameter_name> As <data_type>

where <data_type> is any of the data types listed in Table 22-3. If a parameter is an array, its data type is followed by braces in C# (e.g., string[ ] Name), while the parameter name is followed by parentheses in VB (e.g., Name( ) As String).

For example, one of the versions of the Color class's FromArgb method has the following syntax in C#:

public static Color FromArgb(int red, int green, int blue);

Its VB equivalent is:

Public Shared Function FromArgb(red As Integer, _
                                green As Integer, _
                                blue As Integer) As Color

VB allows methods to be called using either named or positional parameters. If named parameters are used, the parameter name must correspond to that shown in the documentation. For instance, Color.FromArgb can be called as follows using named parameters: NewColor = Color.FromArgb(blue:=125, _ red:=125, green:=125)

C# also uses a number of object-oriented qualifiers with methods. These, and their VB equivalents, are shown in Table 22-4.

Table 22-4. C# keywords used with methods and their VB equivalents

C# keyword	VB keyword
abstract	MustOverride
override	Overrides
sealed	NotOverridable
virtual	Overridable

In both C# and VB, constructors have a special syntax. In C#, constructors have the same name as the classes whose objects they instantiate and do not indicate a return value. For example, the constructor for the Button class is:

public Button( );

In VB, the constructor is represented by a call to a class's New subprocedure. The equivalent call to the Button class constructor in VB is:

Public Sub New( )

22.5.3 Properties

The FileDialog.Title property provides a more or less typical example of a property definition using C# syntax:

public string Title {get; set;}

Like all C# type definitions, the property's data type precedes the property name. The get; and set; property accessors indicate that this is a read-write property. Read-only properties are indicated with a get; only, while write-only properties are indicated with a set; only.

The equivalent VB property definition is:

Public Property Title As String

Note that read-write properties are not decorated with additional keywords in VB. Read-only properties, on the other hand, are indicated with the ReadOnly keyword in front of the Property keyword, while write-only properties have the WriteOnly keyword before the Property keyword.

The shared ProductName property of the Application class is read-only. Its C# syntax appears as follows:

public static string ProductName {get;}

The corresponding VB syntax is:

Public Shared ReadOnly Property ProductName As String

Note that properties, like methods, can use the object-oriented modifiers listed in Table 22-4.

22.5.4 Events

Events are declared in C# using the event keyword, which is followed by the delegate type returned by the event and the name of the event. For example, the Parse event of the Binding class has the following syntax:

public event ConvertEventHandler Parse;

The equivalent VB syntax is:

Public Event Parse As ConvertEventHandler

In addition, the C# event and the VB Event keywords can be preceded by the object modifiers listed in Table 22-4.