ICollection<T> Interface
Definition
Defines methods to manipulate generic collections.
public interface ICollection<T> : System.Collections.Generic.IEnumerable<T>Type Parameters
- T
The type of the elements in the collection.
- Derived
- Implements
-
Examples
The following example implements the ICollection<T> interface to create a collection of custom Box objects named BoxCollection. Each Box has height, length, and width properties, which are used to define equality. Equality can be defined as all dimensions being the same or the volume being the same. The Box class implements the IEquatable<T> interface to define the default equality as the dimensions being the same.
The BoxCollection class implements the Contains method to use the default equality to determine whether a Box is in the collection. This method is used by the Add method so that each Box added to the collection has a unique set of dimensions. The BoxCollection class also provides an overload of the Contains method that takes a specified EqualityComparer<T> object, such as BoxSameDimensions and BoxSameVol classes in the example.
This example also implements an IEnumerator<T> interface for the BoxCollection class so that the collection can be enumerated.
using System;
using System.Collections;
using System.Collections.Generic;
class Program
{
static void Main(string[] args)
{
BoxCollection bxList = new BoxCollection();
bxList.Add(new Box(10, 4, 6));
bxList.Add(new Box(4, 6, 10));
bxList.Add(new Box(6, 10, 4));
bxList.Add(new Box(12, 8, 10));
// Same dimensions. Cannot be added:
bxList.Add(new Box(10, 4, 6));
// Test the Remove method.
Display(bxList);
Console.WriteLine("Removing 6x10x4");
bxList.Remove(new Box(6, 10, 4));
Display(bxList);
// Test the Contains method.
Box BoxCheck = new Box(8, 12, 10);
Console.WriteLine("Contains {0}x{1}x{2} by dimensions: {3}",
BoxCheck.Height.ToString(), BoxCheck.Length.ToString(),
BoxCheck.Width.ToString(), bxList.Contains(BoxCheck).ToString());
// Test the Contains method overload with a specified equality comparer.
Console.WriteLine("Contains {0}x{1}x{2} by volume: {3}",
BoxCheck.Height.ToString(), BoxCheck.Length.ToString(),
BoxCheck.Width.ToString(), bxList.Contains(BoxCheck,
new BoxSameVol()).ToString());
}
public static void Display(BoxCollection bxList)
{
Console.WriteLine("\nHeight\tLength\tWidth\tHash Code");
foreach (Box bx in bxList)
{
Console.WriteLine("{0}\t{1}\t{2}\t{3}",
bx.Height.ToString(), bx.Length.ToString(),
bx.Width.ToString(), bx.GetHashCode().ToString());
}
// Results by manipulating the enumerator directly:
//IEnumerator enumerator = bxList.GetEnumerator();
//Console.WriteLine("\nHeight\tLength\tWidth\tHash Code");
//while (enumerator.MoveNext())
//{
// Box b = (Box)enumerator.Current;
// Console.WriteLine("{0}\t{1}\t{2}\t{3}",
// b.Height.ToString(), b.Length.ToString(),
// b.Width.ToString(), b.GetHashCode().ToString());
//}
Console.WriteLine();
}
}
public class Box : IEquatable<Box>
{
public Box(int h, int l, int w)
{
this.Height = h;
this.Length = l;
this.Width = w;
}
public int Height { get; set; }
public int Length { get; set; }
public int Width { get; set; }
// Defines equality using the
// BoxSameDimensions equality comparer.
public bool Equals(Box other)
{
if (new BoxSameDimensions().Equals(this, other))
{
return true;
}
else
{
return false;
}
}
public override bool Equals(object obj)
{
return base.Equals(obj);
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
public class BoxCollection : ICollection<Box>
{
// The generic enumerator obtained from IEnumerator<Box>
// by GetEnumerator can also be used with the non-generic IEnumerator.
// To avoid a naming conflict, the non-generic IEnumerable method
// is explicitly implemented.
public IEnumerator<Box> GetEnumerator()
{
return new BoxEnumerator(this);
}
IEnumerator IEnumerable.GetEnumerator()
{
return new BoxEnumerator(this);
}
// The inner collection to store objects.
private List<Box> innerCol;
public BoxCollection()
{
innerCol = new List<Box>();
}
// Adds an index to the collection.
public Box this[int index]
{
get { return (Box)innerCol[index]; }
set { innerCol[index] = value; }
}
// Determines if an item is in the collection
// by using the BoxSameDimensions equality comparer.
public bool Contains(Box item)
{
bool found = false;
foreach (Box bx in innerCol)
{
// Equality defined by the Box
// class's implmentation of IEquitable<T>.
if (bx.Equals(item))
{
found = true;
}
}
return found;
}
// Determines if an item is in the
// collection by using a specified equality comparer.
public bool Contains(Box item, EqualityComparer<Box> comp)
{
bool found = false;
foreach (Box bx in innerCol)
{
if (comp.Equals(bx, item))
{
found = true;
}
}
return found;
}
// Adds an item if it is not already in the collection
// as determined by calling the Contains method.
public void Add(Box item)
{
if (!Contains(item))
{
innerCol.Add(item);
}
else
{
Console.WriteLine("A box with {0}x{1}x{2} dimensions was already added to the collection.",
item.Height.ToString(), item.Length.ToString(), item.Width.ToString());
}
}
public void Clear()
{
innerCol.Clear();
}
public void CopyTo(Box[] array, int arrayIndex)
{
if (array == null)
throw new ArgumentNullException("The array cannot be null.");
if (arrayIndex < 0)
throw new ArgumentOutOfRangeException("The starting array index cannot be negative.");
if (Count > array.Length - arrayIndex + 1)
throw new ArgumentException("The destination array has fewer elements than the collection.");
for (int i = 0; i < innerCol.Count; i++) {
array[i + arrayIndex] = innerCol[i];
}
}
public int Count
{
get
{
return innerCol.Count;
}
}
public bool IsReadOnly
{
get { return false; }
}
public bool Remove(Box item)
{
bool result = false;
// Iterate the inner collection to
// find the box to be removed.
for (int i = 0; i < innerCol.Count; i++)
{
Box curBox = (Box)innerCol[i];
if (new BoxSameDimensions().Equals(curBox, item))
{
innerCol.RemoveAt(i);
result = true;
break;
}
}
return result;
}
}
// Defines the enumerator for the Boxes collection.
// (Some prefer this class nested in the collection class.)
public class BoxEnumerator : IEnumerator<Box>
{
private BoxCollection _collection;
private int curIndex;
private Box curBox;
public BoxEnumerator(BoxCollection collection)
{
_collection = collection;
curIndex = -1;
curBox = default(Box);
}
public bool MoveNext()
{
//Avoids going beyond the end of the collection.
if (++curIndex >= _collection.Count)
{
return false;
}
else
{
// Set current box to next item in collection.
curBox = _collection[curIndex];
}
return true;
}
public void Reset() { curIndex = -1; }
void IDisposable.Dispose() { }
public Box Current
{
get { return curBox; }
}
object IEnumerator.Current
{
get { return Current; }
}
}
// Defines two boxes as equal if they have the same dimensions.
public class BoxSameDimensions : EqualityComparer<Box>
{
public override bool Equals(Box b1, Box b2)
{
if (b1.Height == b2.Height && b1.Length == b2.Length
&& b1.Width == b2.Width)
{
return true;
}
else
{
return false;
}
}
public override int GetHashCode(Box bx)
{
int hCode = bx.Height ^ bx.Length ^ bx.Width;
return hCode.GetHashCode();
}
}
// Defines two boxes as equal if they have the same volume.
public class BoxSameVol : EqualityComparer<Box>
{
public override bool Equals(Box b1, Box b2)
{
if ((b1.Height * b1.Length * b1.Width) ==
(b2.Height * b2.Length * b2.Width))
{
return true;
}
else
{
return false;
}
}
public override int GetHashCode(Box bx)
{
int hCode = bx.Height ^ bx.Length ^ bx.Width;
Console.WriteLine("HC: {0}", hCode.GetHashCode());
return hCode.GetHashCode();
}
}
/*
This code example displays the following output:
================================================
A box with 10x4x6 dimensions was already added to the collection.
Height Length Width Hash Code
10 4 6 46104728
4 6 10 12289376
6 10 4 43495525
12 8 10 55915408
Removing 6x10x4
Height Length Width Hash Code
10 4 6 46104728
4 6 10 12289376
12 8 10 55915408
Contains 8x12x10 by dimensions: False
Contains 8x12x10 by volume: True
*/
Imports System.Collections
Imports System.Collections.Generic
Class Program
Public Shared Sub Main(ByVal args() As String)
Dim bxList As BoxCollection = New BoxCollection()
bxList.Add(New Box(10, 4, 6))
bxList.Add(New Box(4, 6, 10))
bxList.Add(New Box(6, 10, 4))
bxList.Add(New Box(12, 8, 10))
' Same dimensions. Cannot be added:
bxList.Add(New Box(10, 4, 6))
' Test the Remove method.
Display(bxList)
Console.WriteLine("Removing 6x10x4")
bxList.Remove(New Box(6, 10, 4))
Display(bxList)
' Test the Contains method
Dim BoxCheck As Box = New Box(8, 12, 10)
Console.WriteLine("Contains {0}x{1}x{2} by dimensions: {3}", BoxCheck.Height.ToString(),
BoxCheck.Length.ToString(), BoxCheck.Width.ToString(), bxList.Contains(BoxCheck).ToString())
' Test the Contains method overload with a specified equality comparer.
Console.WriteLine("Contains {0}x{1}x{2} by volume: {3}", BoxCheck.Height.ToString(),
BoxCheck.Length.ToString(), BoxCheck.Width.ToString(),
bxList.Contains(BoxCheck, New BoxSameVol()).ToString())
End Sub
Public Shared Sub Display(ByVal bxList As BoxCollection)
Console.WriteLine(vbLf & "Height" & vbTab & "Length" & vbTab & "Width" & vbTab & "Hash Code")
For Each bx As Box In bxList
Console.WriteLine("{0}" & vbTab & "{1}" & vbTab & "{2}" & vbTab & "{3}", bx.Height.ToString(), bx.Length.ToString(), bx.Width.ToString(), bx.GetHashCode().ToString())
Next
Console.WriteLine()
End Sub
End Class
Public Class Box : Implements IEquatable(Of Box)
Public Sub New(ByVal h As Integer, ByVal l As Integer, ByVal w As Integer)
Me.Height = h
Me.Length = l
Me.Width = w
End Sub
Private _Height As Integer
Public Property Height() As Integer
Get
Return _Height
End Get
Set(ByVal value As Integer)
_Height = value
End Set
End Property
Private _Length As Integer
Public Property Length() As Integer
Get
Return _Length
End Get
Set(ByVal value As Integer)
_Length = value
End Set
End Property
Private _Width As Integer
Public Property Width() As Integer
Get
Return _Width
End Get
Set(ByVal value As Integer)
_Width = value
End Set
End Property
Public Overloads Function Equals(ByVal other As Box) As Boolean Implements IEquatable(Of Box).Equals
Dim BoxSameDim = New BoxSameDimensions()
If BoxSameDim.Equals(Me, other) Then
Return True
Else
Return False
End If
End Function
Public Overrides Function Equals(ByVal obj As Object) As Boolean
Return MyBase.Equals(obj)
End Function
Public Overrides Function GetHashCode() As Integer
Return MyBase.GetHashCode()
End Function
End Class
Public Class BoxCollection : Implements ICollection(Of Box)
' The generic enumerator obtained from IEnumerator<Box> by GetEnumerator can also
' be used with the non-generic IEnumerator. To avoid a naming conflict,
' the non-generic IEnumerable method is explicitly implemented.
Public Function GetEnumerator() As IEnumerator(Of Box) _
Implements IEnumerable(Of Box).GetEnumerator
Return New BoxEnumerator(Me)
End Function
Private Function GetEnumerator1() As IEnumerator _
Implements IEnumerable.GetEnumerator
Return Me.GetEnumerator()
End Function
' The inner collection to store objects.
Private innerCol As List(Of Box)
Public Sub New()
innerCol = New List(Of Box)
End Sub
' Adds an index to the collection.
Default Public Property Item(ByVal index As Integer) As Box
Get
'If index <> -1 Then
Return CType(innerCol(index), Box)
'End If
'Return Nothing
End Get
Set(ByVal Value As Box)
innerCol(index) = Value
End Set
End Property
' Determines if an item is in the collection
' by using the BoxSameDimensions equality comparer.
Public Function Contains(ByVal item As Box) As Boolean _
Implements ICollection(Of Box).Contains
Dim found As Boolean = False
Dim bx As Box
For Each bx In innerCol
If New BoxSameDimensions().Equals(bx, item) Then
found = True
End If
Next
Return found
End Function
' Determines if an item is in the
' collection by using a specified equality comparer.
Public Function Contains(ByVal item As Box, _
ByVal comp As EqualityComparer(Of Box)) As Boolean
Dim found As Boolean = False
Dim bx As Box
For Each bx In innerCol
If comp.Equals(bx, item) Then
found = True
End If
Next
Return found
End Function
' Adds an item if it is not already in the collection
' as determined by calling the Contains method.
Public Sub Add(ByVal item As Box) _
Implements ICollection(Of Box).Add
If Not Me.Contains(item) Then
innerCol.Add(item)
Else
Console.WriteLine("A box with {0}x{1}x{2} dimensions was already added to the collection.",
item.Height.ToString(), item.Length.ToString(), item.Width.ToString())
End If
End Sub
Public Sub Clear() Implements ICollection(Of Box).Clear
innerCol.Clear()
End Sub
Public Sub CopyTo(array As Box(), arrayIndex As Integer) _
Implements ICollection(Of Box).CopyTo
If array Is Nothing Then
Throw New ArgumentNullException("The array cannot be null.")
Else If arrayIndex < 0 Then
Throw New ArgumentOutOfRangeException("The starting array index cannot be negative.")
Else If Count > array.Length - arrayIndex + 1 Then
Throw New ArgumentException("The destination array has fewer elements than the collection.")
End If
For i As Integer = 0 To innerCol.Count - 1
array(i + arrayIndex) = innerCol(i)
Next
End Sub
Public ReadOnly Property Count() As Integer _
Implements ICollection(Of Box).Count
Get
Return innerCol.Count
End Get
End Property
Public ReadOnly Property IsReadOnly() As Boolean _
Implements ICollection(Of Box).IsReadOnly
Get
Return False
End Get
End Property
Public Function Remove(ByVal item As Box) As Boolean _
Implements ICollection(Of Box).Remove
Dim result As Boolean = False
' Iterate the inner collection to
' find the box to be removed.
Dim i As Integer
For i = 0 To innerCol.Count - 1
Dim curBox As Box = CType(innerCol(i), Box)
If New BoxSameDimensions().Equals(curBox, item) Then
innerCol.RemoveAt(i)
result = True
Exit For
End If
Next
Return result
End Function
End Class
' Defines the enumerator for the Boxes collection.
' (Some prefer this class nested in the collection class.)
Public Class BoxEnumerator
Implements IEnumerator(Of Box)
Private _collection As BoxCollection
Private curIndex As Integer
Private curBox As Box
Public Sub New(ByVal collection As BoxCollection)
MyBase.New()
_collection = collection
curIndex = -1
curBox = Nothing
End Sub
Private Property Box As Box
Public Function MoveNext() As Boolean _
Implements IEnumerator(Of Box).MoveNext
curIndex = curIndex + 1
If curIndex = _collection.Count Then
' Avoids going beyond the end of the collection.
Return False
Else
'Set current box to next item in collection.
curBox = _collection(curIndex)
End If
Return True
End Function
Public Sub Reset() _
Implements IEnumerator(Of Box).Reset
curIndex = -1
End Sub
Public Sub Dispose() _
Implements IEnumerator(Of Box).Dispose
End Sub
Public ReadOnly Property Current() As Box _
Implements IEnumerator(Of Box).Current
Get
If curBox Is Nothing Then
Throw New InvalidOperationException()
End If
Return curBox
End Get
End Property
Private ReadOnly Property Current1() As Object _
Implements IEnumerator.Current
Get
Return Me.Current
End Get
End Property
End Class
' Defines two boxes as equal if they have the same dimensions.
Public Class BoxSameDimensions
Inherits EqualityComparer(Of Box)
Public Overrides Function Equals(ByVal b1 As Box, ByVal b2 As Box) As Boolean
If b1.Height = b2.Height And b1.Length = b2.Length And b1.Width = b2.Width Then
Return True
Else
Return False
End If
End Function
Public Overrides Function GetHashCode(ByVal bx As Box) As Integer
Dim hCode As Integer = bx.Height ^ bx.Length ^ bx.Width
Return hCode.GetHashCode()
End Function
End Class
' Defines two boxes as equal if they have the same volume.
Public Class BoxSameVol
Inherits EqualityComparer(Of Box)
Public Overrides Function Equals(ByVal b1 As Box, ByVal b2 As Box) As Boolean
If (b1.Height * b1.Length * b1.Width) _
= (b2.Height * b2.Length * b2.Width) Then
Return True
Else
Return False
End If
End Function
Public Overrides Function GetHashCode(ByVal bx As Box) As Integer
Dim hCode As Integer = bx.Height ^ bx.Length ^ bx.Width
Console.WriteLine("HC: {0}", hCode.GetHashCode())
Return hCode.GetHashCode()
End Function
End Class
' This code example displays the following output:
' ================================================
'
' A box with 10x4x6 dimensions was already added to the collection.
'
' Height Length Width Hash Code
' 10 4 6 46104728
' 4 6 10 12289376
' 6 10 4 43495525
' 12 8 10 55915408
'
' Removing 6x10x4
'
' Height Length Width Hash Code
' 10 4 6 46104728
' 4 6 10 12289376
' 12 8 10 55915408
'
' Contains 8x12x10 by dimensions: False
' Contains 8x12x10 by volume: True
'
Remarks
The ICollection<T> interface is the base interface for classes in the System.Collections.Generic namespace.
The ICollection<T> interface extends IEnumerable<T>; IDictionary<TKey,TValue> and IList<T> are more specialized interfaces that extend ICollection<T>. A IDictionary<TKey,TValue> implementation is a collection of key/value pairs, like the Dictionary<TKey,TValue> class. A IList<T> implementation is a collection of values, and its members can be accessed by index, like the List<T> class.
If neither the IDictionary<TKey,TValue> interface nor the IList<T> interface meet the requirements of the required collection, derive the new collection class from the ICollection<T> interface instead for more flexibility.
Properties
| Count |
Gets the number of elements contained in the ICollection<T>. |
| IsReadOnly |
Gets a value indicating whether the ICollection<T> is read-only. |
Methods
| Add(T) |
Adds an item to the ICollection<T>. |
| Clear() |
Removes all items from the ICollection<T>. |
| Contains(T) |
Determines whether the ICollection<T> contains a specific value. |
| CopyTo(T[], Int32) |
Copies the elements of the ICollection<T> to an Array, starting at a particular Array index. |
| Remove(T) |
Removes the first occurrence of a specific object from the ICollection<T>. |