I have a class in the code below, where besides equals and hash methods from IEqualityComparer which I use, I also want to implement add, remove, item, count from list and GetEnumerator (current,movenext,position). So I decided to use Inherits CollectionBase, IEnumerator and IEnumerable.
Anyway for instance when I use Add its not going to Add method in Part class, or when I do for each its not going to GetEnumerator move next. What is the problem?
This is the class:
Imports System.Collections.Generic
Public Class Part
Inherits CollectionBase
Implements IEqualityComparer(Of Part), IEnumerator(Of Part), IEnumerable(Of Part)
Private _values As List(Of Part)
Private _currentIndex As Integer
Public Property _comparisonType As EqualsComparmission
Public Sub New(ComparisonType As EqualsComparmission)
Me._comparisonType = ComparisonType
End Sub
Public Sub New(values As List(Of Part))
_values = New List(Of Part)(values)
Reset()
End Sub
Public Sub New()
End Sub
Public Property PartName() As String
Public Property PartId() As Integer
Public Overrides Function ToString() As String
Return "ID: " & PartId & " Name: " & PartName
End Function
Public Sub Add(ByVal value As Part)
Me.List.Add(value)
End Sub
Public Sub Remove(ByVal Index As Integer)
If Index >= 0 And Index < Count Then
List.Remove(Index)
End If
End Sub
Public ReadOnly Property Item(ByVal Index As Integer) As Part
Get
Return CType(List.Item(Index), Part)
End Get
End Property
Public ReadOnly Property Current() As Part
Get
Return _values(_currentIndex)
End Get
End Property
Public ReadOnly Property Current1 As Object Implements IEnumerator.Current
Get
Return Current
End Get
End Property
Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
_currentIndex += 1
Return _currentIndex < _values.Count
End Function
Public Sub Reset() Implements IEnumerator.Reset
_currentIndex = -1
End Sub
#Region "IDisposable Support"
Private disposedValue As Boolean ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
' TODO: dispose managed state (managed objects).
End If
' TODO: free unmanaged resources (unmanaged objects) and override Finalize() below.
' TODO: set large fields to null.
End If
Me.disposedValue = True
End Sub
' TODO: override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
'Protected Overrides Sub Finalize()
' ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
' Dispose(False)
' MyBase.Finalize()
'End Sub
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
Public Function GetEnumerator1() As IEnumerator(Of Part) Implements IEnumerable(Of Part).GetEnumerator
Return CType(Me, IEnumerator)
End Function
Public ReadOnly Property Current2 As Part Implements IEnumerator(Of Part).Current
Get
Return Current
End Get
End Property
Public Function Equals1(x As Part, y As Part) As Boolean Implements System.Collections.Generic.IEqualityComparer(Of Part).Equals
If x Is Nothing AndAlso y Is Nothing Then Return True
If x Is Nothing OrElse y Is Nothing Then Return False
Select Case _comparisonType
Case EqualsComparmission.PartId
Return x.PartId = y.PartId
Case EqualsComparmission.PartName
Return String.Equals(x.PartName, y.PartName)
Case EqualsComparmission.PartId_and_PartName
Return x.PartId = y.PartId AndAlso String.Equals(x.PartName, y.PartName)
Case Else
Throw New NotSupportedException("Unknown comparison type for parts: " & _comparisonType.ToString())
End Select
End Function
Public Function GetHashCode1(obj As Part) As Integer Implements System.Collections.Generic.IEqualityComparer(Of Part).GetHashCode
Select Case _comparisonType
Case EqualsComparmission.PartId
Return obj.PartId
Case EqualsComparmission.PartName
Return If(obj.PartName Is Nothing, 0, obj.PartName.GetHashCode())
Case EqualsComparmission.PartId_and_PartName
Dim hash = 17
hash = hash * 23 + obj.PartId
hash = hash * 23 + If(obj.PartName Is Nothing, 0, obj.PartName.GetHashCode())
Return hash
Case Else
Throw New NotSupportedException("Unknown comparison type for parts: " & _comparisonType.ToString())
End Select
End Function
End Class
and this is test code:
Dim parts As New List(Of Part)()
parts.Add(New Part() With { _
.PartName = "ala", _
.PartId = 11 _
})
parts.Add(New Part() With { _
.PartName = "shift lever", _
.PartId = 1634 _
})
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next
Edited:
PartsCollection which implements ICollection for list operations:
Public Class PartsCollection
Implements ICollection(Of Part)
' Enumerators are positioned before the first element
' until the first MoveNext() call.
Dim position As Integer = -1
Private myList As List(Of Part)
Public Sub New()
If myList Is Nothing Then
myList = New List(Of Part)
End If
End Sub
Public Sub Add(item As Part) Implements ICollection(Of Part).Add
myList.Add(item)
End Sub
Public Sub Clear() Implements ICollection(Of Part).Clear
End Sub
Public Function Contains1(item As Part) As Boolean Implements ICollection(Of Part).Contains
Return myList.Contains(item)
End Function
Public Sub CopyTo(array() As Part, arrayIndex As Integer) Implements ICollection(Of Part).CopyTo
End Sub
Public Function GetEnumerator() As IEnumerator(Of Part) Implements IEnumerable(Of Part).GetEnumerator
Return New PartsEnumeration(myList)
End Function
Public ReadOnly Property Count As Integer Implements ICollection(Of Part).Count
Get
End Get
End Property
Public ReadOnly Property IsReadOnly As Boolean Implements ICollection(Of Part).IsReadOnly
Get
End Get
End Property
Public Function Remove(item As Part) As Boolean Implements ICollection(Of Part).Remove
End Function
Public Function GetEnumerator1() As IEnumerator Implements IEnumerable.GetEnumerator
End Function
End Class
PartsEnumeration for for each loop:
Public Class PartsEnumeration
Implements IEnumerator(Of Part)
Private mmyList As List(Of Part)
Dim position As Integer = -1
Public Sub New(ByVal myList As List(Of Part))
mmyList = myList
End Sub
Public ReadOnly Property Current As Part Implements IEnumerator(Of Part).Current
Get
Try
Return mmyList(position)
Catch ex As IndexOutOfRangeException
Throw New InvalidOperationException()
End Try
End Get
End Property
Public ReadOnly Property Current1 As Object Implements IEnumerator.Current
Get
Try
Return mmyList(position)
Catch ex As IndexOutOfRangeException
Throw New InvalidOperationException()
End Try
End Get
End Property
Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
If position < mmyList.Count - 1 Then
position += 1
Return True
End If
Return False
End Function
Public Sub Reset() Implements IEnumerator.Reset
position = -1
End Sub
#Region "IDisposable Support"
Private disposedValue As Boolean ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
' TODO: dispose managed state (managed objects).
End If
' TODO: free unmanaged resources (unmanaged objects) and override Finalize() below.
' TODO: set large fields to null.
End If
Me.disposedValue = True
End Sub
' TODO: override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
'Protected Overrides Sub Finalize()
' ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
' Dispose(False)
' MyBase.Finalize()
'End Sub
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
End Class
Test code:
Dim cos As New Part With { _
.PartName = "crank arm", _
.PartId = 1234 _
}
Dim cos3 As New Part With { _
.PartName = "cranddk arm", _
.PartId = 123334 _
}
myParts.Add(something1)
myParts.Add(something2)
Dim p As Boolean = myParts.Contains1(something1)
Console.WriteLine(p)
For Each ii In myParts
Console.WriteLine(ii.ToString)
Next
You are gluing 2 things together that are related but not the same thing and making a list of collections.
Dim parts As New List(Of Part)()
Since Part inherits from CollectionBase, you are making a List of Collections. A Collection class should be used to implement methods to manage the list/collection such as the Extension functionality in the other question. It would manage the List for you.
Class Part
Property Name As String
Property ID As Integer
End Class
Class Parts
Private myList As New List(Of Part)
Public Sub Add(item As Part)
Public Function IndexOfPartName...
etc
Public Sub Remove(item As Part)
' some might just be wrappers:
Public Function Contains(p As Part) As Boolean
Return myList.Contains(Part)
End Function
End Class
The code that consumes these:
Friend myParts As New Parts
myParts.Add(New Part(...))
Dim p As Part = myParts.IndexOfPartName("screws")
Once you work out the functionality you need and how it will be used, you might change it to Inherit Collection<T> so you can do For Each p As Part in Parts. But work on getting a viable collection class before tackling interfaces and such. Some of those may not be needed since Collection<T> implements all that for you.
You might be interested in: Guidelines for Collections
--
For your parts collection class to BE a collection rather then be a wrapper for an internal one:
Imports System.ComponentModel
Class Parts
Inherits Collection(Of Part)
' ALREADY implemeted for you are:
' Contains, Count, Add, Clear, IndexOf, Insert, EQUALS
' Item, Items, Remove, RemoveAt and RemoveItem
As such, all you need to do is override those methods which do something differently than you would like, or to extend functionality such as a IndexOfPartName.
ICollection requires you to write a collection from scratch, but the wheel has already been built.