VB .net tutorial - 13

8/14/2019 VB .net tutorial - 13

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Creating Components

NIIT Creating Components/Lesson 13/Slide 1 of 19

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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Just a Minute

You need to write a program to validate user logins. Thisprogram will be used across applications. What will youdevelop the program as and why?


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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 nameconflicts. To avoid this conflict you can also give ashared name to an assembly.


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Just a Minute

Why does an assembly need a shared name?


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Creating Components


Component Classes

Get created when they follow defined standards ofinteraction provided by the IComponent interface.

Can be created by using the .NET Class Library projecttemplate.

Can be used in another project by adding a reference to thecomponents.


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Just a Minute

How will you use a component?


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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 thatthere are no references to the component and thereforeit calls the Finalize() method of the component.


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Polymorphism

Is the ability of a class to implement functions with the samename to perform different actions depending on how theyare 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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COM in .NET

.NET supports COM and ActiveX objects for backwardcompatibility.

Interaction between COM and .NET is provided through awrapper called RuntimeCallableWrapper (RCW).

A COM component can be called from .NET in the followingways:

By converting the COM type library to a .NET assemblyby using the tlbimp tool

Using COM components directly by adding a reference


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Problem Statement 13.D.1

Customers of Diaz Telecommunications who place theirorders online must submit their credit card number, name, andthe expiry date of the credit card. The credit card numbersubmitted has to be validated.


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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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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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Task 2: Identify the properties and methods for thecomponent. (Contd.)

Result:

RightChar(): A method to return the rightmost characterfrom a string.

CharaceterToInt(): A method to return the numericalequivalent of a character.

Validate(): A method to validate the card number.


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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.


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Problem Statement 13.P.1

The Employee data in the call centers at DiazTelecommunications requires check for valid employee id,age, and salary entries. The employee id should start with theletter E followed by three digits. The age should be from 21years to 60 years. In addition, the salary should be in therange of $3000 to $35000. Create a component that will checkthe validity of employee id, age, and salary.


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Summary

In this lesson, you learned that:

A component is a reusable piece of code in a binary formthat can be plugged into components from other

vendors, with relatively little effort.

An assembly contains information about the files on whichthe component depends and the location of these files.

An interface can be implemented in a class to implementpolymorphism.

ComponentObjectModule (COM) is alanguage 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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VB .net tutorial - 13