This document discusses creating and using components in .NET. It explains that a component is a reusable piece of code that can reduce development time. An assembly contains metadata about a component's dependencies and location. The document also discusses implementing interfaces for polymorphism and using COM components in .NET by converting type libraries or adding references. It provides an example problem of validating credit card numbers for an e-commerce site.

1. Creating Components
Objectives
In this lesson, you will learn to:
Create components for Windows Forms
Use COM components in Visual Basic .NET
Implement an Interface in Visual Basic .NET
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2. Creating Components
Component
Is a reusable piece of code in a binary form that can be
plugged into components from other vendors, with relatively
little effort.
Helps in reducing the development time.
Helps in reducing errors because you reuse a code that is
already tested.
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3. Creating Components
Just a Minute…
You need to write a program to validate user logins. This
program will be used across applications. What will you
develop the program as and why?
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4. Creating Components
Component Architecture in .NET
Assembly
Contains information about the files on which the
component depends and the location of these files.
Consists of a manifest and the portable executables
(PE).
Global Assembly Cache
Is a repository of assemblies.
Must have a unique identification to resolve name
conflicts. To avoid this conflict you can also give a
shared name to an assembly.
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5. Creating Components
Just a Minute…
Why does an assembly need a shared name?
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6. Creating Components
Component Classes
Get created when they follow defined standards of
interaction provided by the IComponent interface.
Can be created by using the .NET Class Library project
template.
Can be used in another project by adding a reference to the
components.
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7. Creating Components
Just a Minute…
How will you use a component?
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8. Creating Components
Life Cycle of a Component
Initialization phase
Can be of two types:
®Type initialization
®Instance initialization
Cleanup phase
Is implemented by using the Dispose() method.
Destroy phase
Gets invoked when the garbage collector finds that
there are no references to the component and therefore
it calls the Finalize() method of the component.
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9. Creating Components
Polymorphism
Is the ability of a class to implement functions with the same
name to perform different actions depending on how they
are called.
Is a feature supported by all object-oriented languages.
Can be implemented in three ways:
By implementing an interface
By using inheritance
By using abstract classes
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10. Creating Components
COM in .NET
.NET supports COM and ActiveX objects for backward
compatibility.
Interaction between COM and .NET is provided through a
wrapper called Runtime‑Callable Wrapper (RCW).
A COM component can be called from .NET in the following
ways:
By converting the COM type library to a .NET assembly
by using the tlbimp tool
Using COM components directly by adding a reference
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11. Creating Components
Problem Statement 13.D.1
Customers of Diaz Telecommunications who place their
orders online must submit their credit card number, name, and
the expiry date of the credit card. The credit card number
submitted has to be validated.
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12. Creating Components
Task List
Identify the most suitable type of component.
Identify the properties and methods for the component.
Create a project of the appropriate type.
Add properties and functions to the component.
Build the component.
Create a user interface to display the result.
Verify the execution.
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13. Creating Components
Task 1: Identify the most suitable type of component.
Result:
A customized component has to be created to verify the
credit card numbers supplied by the customers.
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14. Creating Components
Task 2: Identify the properties and methods for the
component.
You can have the following types of constructors in your
component:
Public Constructors — To enable developers to create
instances of your component.
Friend Constructors — To enable the usage of a
component inside an assembly but not outside it.
Private Constructors — To enable the usage only inside
the component class.
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15. Creating Components
Task 2: Identify the properties and methods for the
component. (Contd.)
Result:
The two properties required for the components are:
 CustomerName: A property for the name of the
customer of type string.
 CardNumber: A property for the card number of type
string.
The following methods are required:
 The default public constructor can be used for this
component.
 LeftChar(): A method to return the leftmost character
from a string.
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16. Creating Components
Task 2: Identify the properties and methods for the
component. (Contd.)
Result:
RightChar(): A method to return the rightmost character
from a string.
CharaceterToInt(): A method to return the numerical
equivalent of a character.
Validate(): A method to validate the card number.
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17. Creating Components
Task 3: Create a project of the appropriate type.
Task 4: Add properties and functions to the
component.
Task 5: Build the component.
Task 6: Create a user interface to display the result.
Task 7: Verify the execution.
©NIIT Creating Components/Lesson 13/Slide 17 of 19

18. Creating Components
Problem Statement 13.P.1
The Employee data in the call centers at Diaz
Telecommunications requires check for valid employee id,
age, and salary entries. The employee id should start with the
letter ‘E’ followed by three digits. The age should be from 21
years to 60 years. In addition, the salary should be in the
range of $3000 to $35000. Create a component that will check
the validity of employee id, age, and salary.
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19. Creating Components
Summary
In this lesson, you learned that:
A component is a reusable piece of code in a binary form
that can be plugged into components from other
vendors, with relatively little effort.
An assembly contains information about the files on which
the component depends and the location of these files.
An interface can be implemented in a class to implement
polymorphism.
Component Object Module (COM) is a
language‑independent software architecture that defines a set
of standards for component interoperability.
COM components can be used in .NET by using the tlbimp
tool or by adding a reference.
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