The document discusses creating and using .NET components. It covers identifying different types of components, the life cycle of a component, implementing polymorphism in components, using COM components in .NET, declaring properties and methods for a component, referencing the component from a user interface, and the role of assemblies in .NET.

1. Creating Components
Objectives
In this lesson, students will learn to:
• Identify the types of components
• Identify the various stages in the life cycle of a component
• Implement polymorphism in components
• Use .NET COM components in VB.NET
• Declare properties and methods for a component
• Create a reference of the Component from the User Interface
• Identify the role of assemblies in VB.NET
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2. Creating Components
Getting Started with .NET
Components
• A component is a binary executable built from a .NET project.
• The component is referenced by applications seeking the services provided by
the component.
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3. Creating Components
Introducing Components
• You can create the component once and reuse it whenever necessary.
• You can also develop components as a third party provider.
• When you use the components, you are not inheriting a class but using a
binary code in your applications.
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4. Creating Components
Types of Components
• Components can be of three types:
• In-built Components
• The .NET class framework comes with in-built components, such as
Timer and ServiceController.
• You can use the components that come with the .NET class
framework in your applications.
• Component Classes
• A class becomes a component when it follows defined standards of
interaction.
• All components derive from the Component class.
• User Controls
• User Controls can be defined as bundles of standard controls.
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5. Creating Components
Characteristics of a Component
• The name of a component class should be short and meaningful. It should be a
combination of whole words with a capitalized initial character for each word.
• You can control the use of a component by using proper access level for the
constructors.
• You can implement the IComponent interface to create a component.
• You should group related components together in separate namespaces.
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6. Creating Components
Life Cycle of a Component
• Components are initialized by constructors.
• Initialization can be of two types:
• Type initialization
• Type initialization is achieved by using a shared constructor.
• Shared constructor is called only once in the lifetime of a Visual Basic
.NET application.
• Instance initialization.
• Instance initialization can be achieved by using constructors, which
are not shared.
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7. Creating Components
Polymorphism in Components
• The ability of a class to implement functions with the same name that are
performing different actions depending on how they are called is known as
polymorphism.
• Polymorphism can be implemented by:
• Implementing an interface.
• Inheritance
• Using abstract classes.
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8. Creating Components
Implementing Interfaces
• An interface defines the behavior of a class.
• An interface can declare properties, methods, and events.
• An interface can be implemented by more than one class.
• An interface can be declared as :
Interface interfacename
Sub functionname()
End Interface
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9. Creating Components
Using .NET COM Components in
VB.NET
• Component Object Model (COM) was used in earlier versions of Visual Basic to
create components.
• Implementation of COM is called ActiveX.
• The .NET supports COM and ActiveX objects for backward compatibility.
• A COM component from .NET can be called in the following ways:
• By converting the COM type library to a .NET assembly.
• Using COM components directly.
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10. Creating Components
Converting COM Type Library to .NET
Assembly
• The tlbimp tool can be used to convert a COM type library to a .NET assembly.
• Following options can be used with tlbimp tool:
• out:FileName – specifies the name of the assembly to be produced.
• Namespace:NameSpace – Specifies the namespace of the assembly to be
produced.
• AsmVersion:Version – Specifies version number of the assembly to be
produced.
• reference:FileName – Specifies the file name to be used to resolve
references.
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11. Creating Components
Using COM Components Directly
• The Com components can be added directly through Solution Explorer in .NET.
• Internally, an Runtime Callable Wrapper (RCW) is used to access the COM
components.
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12. Creating Components
Using COM+ with VB.NET
• COM+ is the basic COM and a set of additional services.
• COM+ programming is based on the following assumptions:
• In COM+, clients program on the basis of Interfaces, not Classes.
• Code is not linked statically.
• Using Com+ components, you can focus on developing business logic.
• A .NET component that takes advantage of COM+ services needs to be derived
from the .NET base class ServicedComponent.
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13. Creating Components
Properties and Methods for a
Component
• To create a component in .NET, the user needs to identify:
• The type of component.
• Properties for the component.
• Methods for the component.
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14. Creating Components
Using Constructors
• A component can have the following types of constructors:
• Public constructors.
• Friend constructors.
• Private constructors.
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15. Creating Components
Adding properties
• Declaring a property allows you to control how a value is changed or read.
• Calculated values can be shown as properties even when they are not stored
as actual data in the class.
• Property statement can also incorporate error handling.
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16. Creating Components
Adding methods
• If a method is declared Private, only methods within the same class can call
that method.
• A method in a class is a procedure that performs some sort of operation on the
data within the class and may or may not return.
• A method is declared as:
Public Function functionname() As Integer
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17. Creating Components
Referencing the Component from the
User Interface
• A component can be tested only by referencing it from another application.
• A component can be referenced by using the Solution Explorer.
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18. Creating Components
Role of Assemblies in VB.NET
• Concept of assemblies has been introduced in the .NET to counter the problems
faced in DLL handling in previous versions.
• An assembly usually consists of:
• Manifest
• This contains the information like name and version of the assembly.
• Information about the files that the assembly uses, is also present in
it.
• Portable executable (PE)
• This contains metadata, Intermediate Language (IL) and the type
information.
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19. Creating Components
Demo
Using .NET Components
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20. Creating Components
Problem Statement
• Build a .NET DLL component ‘PickServerTime’ which can get the current date
and time from the host computer and then use the component in another
VB.NET application named as ConsumerApplication which will display the
information.
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21. Creating Components
Solution
• To build and use the ‘PickServerTime’ component in an application named as
‘ConsumerApplication’ , you need to perform the following steps:
1. Create a project.
2. Add properties and functions to the component.
3. Build the component.
4. Create a user interface to test the component.
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22. Creating Components
Summary
In this lesson, you learned that:
• A component is a reusable piece of code in binary form that can be used
along with the components from other vendors, with relatively little effort.
• Types of Components:
• In-built components.
• Component classes.
• User controls.
• A component goes through different stages once you deploy it. The
constructors initialize components.
• Initialization can be of two types:
• Type initialization.
• Instance initialization.
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23. Creating Components
Summary (Contd.)
• In .NET programming environment, COM components are called:
• By converting the COM type library to a .NET assembly.
• By using COM components directly.
• The tlbimp tool uses the metadata of a COM type library to do the
conversion.
• To create a component in .NET, the user firstly needs to identify the type of
component and also its properties and methods.
• In .NET programming environment, a component can have the following
types of constructors:
• Public constructor.
• Friend constructor.
• Private constructor
• An assembly contains information about the files on which the component
depends and the location of these files.
• An assembly consists of a manifest and the portable executables (PE).
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24. Creating Components
Summary (Contd.)
• A manifest consists of information such as the name and version of the
assembly.
• A portable executable consists of the IL code, type information, and
metadata.
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