http://www.codeproject.com/Articles/642505/Advantage-of-using-Interface-and-Inheritance-in-VB
If you are doing Object Oriented Programming you will see Interfaces come into play in design patterns.
https://www.safaribooksonline.com/library/view/visual-basic-design/0201702657/
Here is a classic design pattern used in a Data Access Layer, another design pattern, called a DAO Data Access Object pattern.
https://en.wikipedia.org/wiki/Data_access_object
Here you see the DAO pattern being implemented in the link.
http://www.tutorialspoint.com/design_pattern/data_access_object_pattern.htm
You see Interfaces used heavily in .NET solutions that implement the programming principles explained in the link, which is highly sought out expertise in .NET developers that know it and how to use it.
http://www.codeproject.com/Articles/465173/Dependency-Inversion-Principle-IoC-Container-Depen
Below you see the DAO pattern in action in the code below.
See if you can implement Interface usage in the simple VB N-tier, another design pattern, solution by implementing Interfaces on the BLL and DAL classes.
http://www.codeproject.com/Articles/21115/Building-an-N-Tier-Application-in-VB-NET-in-Step
https://en.wikipedia.org/wiki/Multitier_architecture
https://en.wikipedia.org/wiki/Separation_of_concerns
What is being talked about is implemented in .NET enterprise level solutions all of the time.
Imports Entities
Imports System.Collections.Generic
Public Interface IArticleDao
Function GetArticle(id As Int32) As DTOArticle
Function GetArticles() As List(Of DTOArticle)
Sub UpdateArticles(articles As List(Of DTOArticle))
Sub AddArticles(articles As List(Of DTOArticle))
Sub DeleteArticle(article As DTOArticle)
End Interface
Imports System.Collections.Generic
Imports Entities
Imports System.Data.EntityClient
Namespace DAL
Public Class ArticleDao
Implements IArticleDao
Private Const pcdb As String = "name=PublishingCompanyEntities"
Public Sub AddArticles(articles As List(Of Entities.DTOArticle)) Implements IArticleobj.AddArticles
Dim conn = New EntityConnection(pcdb)
Dim db = New PublishingCompanyEntities(conn)
Using conn
Using db
Try
For Each article In articles
Dim artc = New Article With {.AuthorID = article.AuthorID, .Title = article.Title.Trim, .Body = article.Body.Trim}
db.AddToArticles(artc)
db.SaveChanges()
Next
Finally
conn.Close()
End Try
End Using
End Using
End Sub
Public Sub DeleteArticle(article As Entities.DTOArticle) Implements IArticleobj.DeleteArticle
Dim thearticle = New Article With {.ArticleID = article.ArticleID}
Dim conn = New EntityConnection(pcdb)
Dim db = New PublishingCompanyEntities(conn)
Using conn
Using db
Try
db.AttachTo("Articles", thearticle)
db.DeleteObject(thearticle)
db.SaveChanges()
Finally
conn.Close()
End Try
End Using
End Using
End Sub
Public Function GetArticle(id As Integer) As Entities.DTOArticle Implements IArticleobj.GetArticle
Dim dto = New DTOArticle
Dim conn = New EntityConnection(pcdb)
Dim db = New PublishingCompanyEntities(conn)
Using conn
Using db
Try
Dim thearticle = (From p In db.Articles
Where p.ArticleID = id
Select p).FirstOrDefault()
If Not IsNothing(thearticle) Then
dto.ArticleID = thearticle.ArticleID
dto.AuthorID = thearticle.AuthorID
dto.Title = thearticle.Title.Trim
dto.Body = thearticle.Body.Trim
End If
Finally
conn.Close()
End Try
End Using
End Using
Return dto
End Function
Public Function GetArticles() As List(Of Entities.DTOArticle) Implements IArticleobj.GetArticles
Dim dtos = New List(Of DTOArticle)
Dim conn = New EntityConnection(pcdb)
Dim db = New PublishingCompanyEntities(conn)
Using conn
Using db
Try
Dim results = (From a In db.Articles Select a).ToList
dtos.AddRange(results.Select(Function(a) New DTOArticle With {.ArticleID = a.ArticleID,
.AuthorID = a.AuthorID,
.Title = a.Title.Trim,
.Body = a.Body.Trim}))
Finally
conn.Close()
End Try
End Using
End Using
Return dtos
End Function
Public Sub UpdateArticles(articles As List(Of Entities.DTOArticle)) Implements IArticleobj.UpdateArticles
Dim conn = New EntityConnection(pcdb)
Dim db = New PublishingCompanyEntities(conn)
Using conn
Using db
Try
For Each art In articles
Dim thearticle = New Article() With {.ArticleID = art.ArticleID}
db.AttachTo("Articles", thearticle)
thearticle.AuthorID = art.AuthorID
thearticle.Title = art.Title.Trim
thearticle.Body = art.Body.Trim
db.SaveChanges()
Next
Finally
conn.Close()
End Try
End Using
End Using
End Sub
End Class
End Namespace
