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Constructor (VB.Net and Access VBA Cross Reference Guide)

By Mike Prestwood

VB.Net versus Access VBA: A side by side comparison between VB.Net and Access VBA.

 
OOP Details
 

More object oriented (OO) stuff.

Constructor

[Other Languages] 

General Info: Class Constructor

Constructors are called when you instantiate an object from a class. This is where you can initialize variables and put code you wish executed each time the class is created. When you initially set the member fields and properties of an object, you are initializing the state of the object. The state of an object is the values of all it's member fields and properties at a given time.

Languages Focus

What is the syntax? Can you overload constructors? Is a special method name reserved for constructors?

VB.Net:  "Constructors" New

In VB.Net, a constructor is called whenever a class or struct is created. A constructor is a sub named New. You can overload the constructor simply by adding two or more New subs with various parameters (overloaded constructors).

If you do not create a constructor, VB.Net will create an implicit constructor that initializes all member fields to their default values.

Constructors can execute at two different times. Static constructors are executed by the CLR before any objects are instantiated. Regular constructors are executed when you create an object.

You can invoke the parent constructor with MyBase.New.

Syntax Example:
Public Class Cyborg
Public CyborgName As String
  
  Public Sub New(ByVal pName As String)
CyborgName = pName
End Sub
End Class
Access VBA:  "Constructors" Class_Initialize

When an object instance is created from a class, Access VBA calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, Access VBA calls a special sub called Class_Terminate.

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