Programming | VB.NET Language Pocket Reference

1.26 Programming

AddHandler Statement

AddHandler NameOfEventSender, AddressOf NameOfEventHandler

NameOfEventSender required; String literal

The name of a class or object instance and its event, such as Button1.Click

NameOfEventHandler required; String literal

The name of a subroutine that is to serve as the event handler for NameOfEventSender

Description

Binds an event handler to a built-in or custom event. This makes it possible to bind several event handlers to a single event.

NameOfEventSender takes the form class.event or object.event

You can stop handling events defined by the AddHandler statement by calling the RemoveHandler statement

AddressOf Operator

AddressOf procedurename

procedurename required

The name of a procedure that is referenced by the procedure delegate

Description

The AddressOf operator returns a procedure delegate instance that references a specific procedure. It is used in the following situations:

If a parameter to a procedure (a VB procedure or a Win32 API function) requires a function pointer (the address of a function), then we can pass the expression:

AddressOf functionname

where functionname is the name of the function. This function is called a callback function.

AddressOf is also used to create delegate objects, as in:

delg = New ADelegate(AddressOf obj.AMethod)

AddressOf is used to bind event handlers to events through the AddHandler statement:

AddHandler Form1.Click, AddressOf Me.Form1Click

Class...End Class Statement

See Class...End Class Statement entry under Section 1.16.

COMClass Attribute

Microsoft.VisualBasic.COMClassAttribute

Description

Adds metadata that allows a .NET class to be exposed as a COM object. You can supply the attribute with a class identifier, an interface identifier, and an event identifier. All are globally unique identifiers (GUIDs) that can be generated either by using the guidgen.exe utility or automatically by using the COM Class Wizard. They ensure that the COM component retains the same GUIDs when it is recompiled.

Constructor

New([[[classID], interfaceID], eventID])

classID String

The class identifier (CLSID) that will uniquely identify the COM class

interfaceID String

The interface identifier (IID) that uniquely identifies the class' default COM interface

eventID String

The event identifier that uniquely identifies an event

Properties

ClassID String

Read-only. Provides the CLSID that uniquely identifies a COM class. Its value is set by the classID parameter of the class constructor.

EventID String

Read-only. Provides the GUID that uniquely identifies an event. Its value is set by the eventID parameter of the class constructor.

InterfaceID String

Read-only. Provides the IID that uniquely identifies a COM interface. Its value is set by the interfaceID parameter of the class constructor.

InterfaceShadows Boolean

Indicates whether the COM interface name is the same as the name of another member of the class or the base class. Its default value is False.

CreateObject Function

Microsoft.VisualBasic.Interaction

objectvariable = CreateObject(progid [, servername])

objectvariable required; Object

A variable to hold the reference to the instantiated object

progid required; String

The programmatic identifier (or ProgID) of the class of the object to create

servername optional; String

The name of the server on which the object resides

Named Arguments

Return Value

A reference to a COM or ActiveX object

Description

Creates an instance of an OLE Automation (ActiveX) object.

Prior to calling the methods, functions, or properties of a COM or ActiveX object, you are required to create an instance of that object. Once an object is created, reference it in code using the object variable you defined.

Declare Statement

See Declare Statement entry under Section 1.16.

Event Statement

[accessmodifier] [Shadows] Event eventName [(arglist)]

[Implements interfacename.interfaceeventname]

accessmodifier optional; Keyword

Can be one of Public, Private, Protected, Friend, and ProtectedFriend.

Shadows optional; Keyword

Indicates that the event shadows any programming elements of the same name in a base class.

eventName required; String literal

The name of the event.

arglist

is optional and has the following syntax:

[ByVal | ByRef] varname[( )] [As type]

ByVal optional; Keyword

The argument is passed by value; that is, a local copy of the variable is assigned the value of the argument. ByVal is the default method of passing variables.

ByRef optional; Keyword

The argument is passed by reference; that is, the local variable is simply a reference to the argument being passed. All changes made to the local variable are reflected in the calling argument.

varname required; String literal

The name of the local variable containing either the reference or value of the argument.

type optional; Keyword

The data type of the argument. It can be Byte, Boolean, Char, Short, Integer, Long, Single, Double, Decimal, Date, String, Object, or any user-defined structure, object type, or data type defined in the BCL.

Implementsinterfacename.interfaceeventname optional

Indicates that the event implements a particular event named interfaceeventname in the interface named interfacename.

Description

Defines a custom event that the object can raise at any time using the RaiseEvent statement.

Environ Function

See Environ Function entry under Section 1.23.

Get Statement

Get(  )

  [ statements ]

End Get

statements optional

Program code to be executed when the Property Get procedure is called

Description

Defines a Property Get procedure that returns a property value to the caller.

GetObject Function

Microsoft. VisualBasic.Interaction

GetObject([pathname] [, class])

pathname optional; String

The full path and name of the file containing the COM (or ActiveX) object.

class optional; String

The class of the object. The class argument has these parts:

Appname required; String

The name of the application.

Objecttype required; String

The class of object to create, delimited from Appname by using a period ( . ). For example, Appname.Objecttype.

Return Value

A reference to an ActiveX object

Description

Accesses an ActiveX server held within a specified file.

Handles Keyword

Handles name.event

name required; String literal

The name of the class or object whose event the subroutine is handling

event required; String literal

The name of the event that the subroutine is handling

Description

Defines a procedure as the event handler for a particular event.

Implements Keyword

Implements interfacename.interfacemember [, ...]

interfacename required; String literal

The name of the interface being implemented by a class

interfacemember required; String literal

The name of the interface property, function, procedure, or event that is being implemented by a class

Description

Indicates that a class member provides the implementation of a member defined in an interface.

Implements Statement

Implements InterfaceName [,InterfaceName][,...]

InterfaceName required; String literal

The name of the interface that a class implements

Description

The Implements statement specifies that you will implement an interface within the class in which the Implements statement appears.

Imports Statement

Imports [aliasname = ] namespace [.element]

aliasname optional; String literal

The name by which the namespace will be referenced in the module

namespace required; String literal

The name of the namespace being imported

element optional

The name of an element in the namespace

Description

Imports namespaces or parts of namespaces, making their members available to the current module.

Inherits Statement

Inherits classname

classname required; String literal

The name of the inherited (base) class

Description

Specifies the name of the class that is being inherited, that is, the base class. The statement can appear immediately after the Class statement or the Interface statement.

Interface Statement

[ accessmodifier ] [Shadows] Interface name

...statements

End Interface

accessmodifier optional; Keyword

One of the following keywords, which determines the visibility of the interface:

Public optional; Keyword

Indicates that the interface is publicly accessible anywhere both inside and outside of the project.

Private optional; Keyword

Indicates that the interface is accessible to any nested types, as well as to the type (if any) in which it is defined.

Protected optional; Keyword

Indicates that the interface is accessible only to derived classes; a protected interface can only be declared inside of a class.

Friend optional; Keyword

Indicates that the interface is accessible only within the project that contains the interface definition.

Protected Friend optional; Keyword

Indicates that the interface is declared inside of a class and that it is accessible throughout the project that contains the interface definition, as well as to derived classes.

Shadows optional; Keyword

Indicates that the interface shadows an identically named element in a base class.

name required; String literal

The name of the interface.

statements required

Code that defines the interface members that derived classes must implement.

Description

Defines a virtual base class along with its public members. The interface can then be implemented by derived classes using the Implements statement.

Is Operator

object1 Is object2

object1  required; Object or any reference type

object2   required; Object or any reference type

Return Value

Boolean

Description

Compares two object variables or reference variables to determine whether they reference the same object.

Len Function

Microsoft.VisualBasic.Strings

Len(expression)

expression required; any

Any valid variable name or expression

Return Value

Integer

Description

Counts the number of characters within a string or the size of a given variable.

Me Operator

Me

Description

Represents a reference to the current class from within the class.

MyBase Keyword

MyBase

Description

Provides a reference to the base class from within a derived class. If you want to call a member of the base class from within a derived class, you can use the syntax:

MyBase.MemberName

where MemberName is the name of the member. This will resolve any ambiguity if the derived class also has a member of the same name.

MyClass Keyword

MyClass

Description

Provides a reference to the class in which the keyword is used.

Namespace Statement

Namespace name

  component types

End Namespace

name required; String literal

The name of the namespace

component types required

The elements that are being declared as part of the namespace, including Enums, Structures, Interfaces, Classes, Delegates, Modules, and other namespaces

Description

Declares a namespace and specifies the items in it.

Property Statement

See Property Statement entry under Section 1.16.

RaiseEvent Statement

RaiseEvent eventName([arglist])

eventName required; String literal

The name of the event

arglist optional; any (defined by the Event statement)

A comma-delimited list of arguments

Description

Generates a predefined, custom event within any procedure of an object module

RemoveHandler Statement

RemoveHandler NameOfEventSender, AddressOf NameOfEventHandler

NameOfEventSender required; String literal

The name of a class or object instance and its event, such as Button1.Click

NameOfEventHandler required; String literal

The name of a subroutine to remove as event handler for NameOfEventSender

Description

Removes a previous binding of an event handler to a built-in or custom event.

Shadows Keyword

Shadows

Description

When a member of a derived class has the same name as a member of the same type in the base class, and the keywords Overridable and Overrides are used appropriately, then the derived class member overrides the base class member. That is, any reference to the member using a derived class object refers to the implementation in the derived class.

Shadowing works in a similar way but allows any member type to "override" any other member type. Thus, for example, a method can "override" a property.

SyncLock Statement

SyncLock expression

...[ code ]

End SyncLock

expression required; any reference type (class, module, interface, array, or delegate)

An expression yielding a single result that can be used to determine the accessibility of code

code optional

The code statements to which access is synchronized and that will be executed sequentially

Description

Prevents multiple threads of execution in the same process from accessing shared data or resources at the same time

WithEvents Keyword

Dim|Private|Public WithEvents objVarName As objectType

objVarName required; String

The name of any object variable that refers to an object that exposes events

objectType required; any object type other than the generic Object

The ProgID of a referenced object

Description

Informs VB that the object being referenced exposes events for which you intend to provide event handlers.