IList Interface

Represents a non-generic collection of objects that can be individually accessed by index.

Imports System.Collections
Public Class Example
 Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
 Dim myList As New SimpleList()
 ' Populate the List
 outputBlock.Text &= "Populate the List" & vbCrLf
 myList.Add("one")
 myList.Add("two")
 myList.Add("three")
 myList.Add("four")
 myList.Add("five")
 myList.Add("six")
 myList.Add("seven")
 myList.Add("eight")
 myList.PrintContents(outputBlock)
 outputBlock.Text &= vbCrLf
 ' Remove elements from the list
 outputBlock.Text &= "Remove elements from the list" & vbCrLf
 myList.Remove("six")
 myList.Remove("eight")
 myList.PrintContents(outputBlock)
 outputBlock.Text &= vbCrLf
 ' Add an element to the end of the list
 outputBlock.Text &= "Add an element to the end of the list" & vbCrLf
 myList.Add("nine")
 myList.PrintContents(outputBlock)
 outputBlock.Text &= vbCrLf
 ' Insert an element into the middle of the list
 outputBlock.Text &= "Insert an element into the middle of the list" & vbCrLf
 myList.Insert(4, "number")
 myList.PrintContents(outputBlock)
 outputBlock.Text &= vbCrLf
 ' Check for specific elements in the list
 outputBlock.Text &= "Check for specific elements in the list" & vbCrLf
 outputBlock.Text += String.Format("List contains 'three': {0}", myList.Contains("three")) & vbCrLf
 outputBlock.Text += String.Format("List contains 'ten': {0}", myList.Contains("ten")) & vbCrLf
 End Sub
End Class ' class Program
Public Class SimpleList
 Implements IList
 Private _contents(8) As Object
 Private _count As Integer
 Public Sub New()
 _count = 0
 End Sub
 ' IList Members
 Public Function Add(ByVal value As Object) As Integer Implements IList.Add
 If (_count < _contents.Length - 1) Then
 _contents(_count) = value
 _count = _count + 1
 Return (_count - 1)
 Else
 Return -1
 End If
 End Function
 Public Sub Clear() Implements IList.Clear
 _count = 0
 End Sub
 Public Function Contains(ByVal value As Object) As Boolean Implements IList.Contains
 Dim inList As Boolean = False
 Dim i As Integer
 For i = 0 To Count
 If _contents(i) = value Then
 inList = True
 Exit For
 End If
 Next i
 Return inList
 End Function
 Public Function IndexOf(ByVal value As Object) As Integer Implements IList.IndexOf
 Dim itemIndex As Integer = -1
 Dim i As Integer
 For i = 0 To Count
 If _contents(i) = value Then
 itemIndex = i
 Exit For
 End If
 Next i
 Return itemIndex
 End Function
 Public Sub Insert(ByVal index As Integer, ByVal value As Object) Implements IList.Insert
 If (_count + 1) <= (_contents.Length - 1) And (index < Count) And (index >= 0) Then
 _count = _count + 1
 Dim i As Integer
 For i = Count - 1 To index
 _contents(i) = _contents(i - 1)
 Next i
 _contents(index) = value
 End If
 End Sub
 Public ReadOnly Property IsFixedSize() As Boolean Implements IList.IsFixedSize
 Get
 Return True
 End Get
 End Property
 Public ReadOnly Property IsReadOnly() As Boolean Implements IList.IsReadOnly
 Get
 Return False
 End Get
 End Property
 Public Sub Remove(ByVal value As Object) Implements IList.Remove
 RemoveAt(IndexOf(value))
 End Sub
 Public Sub RemoveAt(ByVal index As Integer) Implements IList.RemoveAt
 If index >= 0 And index < Count Then
 Dim i As Integer
 For i = index To Count - 1
 _contents(i) = _contents(i + 1)
 Next i
 _count = _count - 1
 End If
 End Sub
 Public Property Item(ByVal index As Integer) As Object Implements IList.Item
 Get
 Return _contents(index)
 End Get
 Set(ByVal value As Object)
 _contents(index) = value
 End Set
 End Property
 ' ICollection Members
 Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) Implements ICollection.CopyTo
 Dim j As Integer = index
 Dim i As Integer
 For i = 0 To Count
 array.SetValue(_contents(i), j)
 j = j + 1
 Next i
 End Sub
 Public ReadOnly Property Count() As Integer Implements ICollection.Count
 Get
 Return _count
 End Get
 End Property
 Public ReadOnly Property IsSynchronized() As Boolean Implements ICollection.IsSynchronized
 Get
 Return False
 End Get
 End Property
 ' Return the current instance since the underlying store is not
 ' publicly available.
 Public ReadOnly Property SyncRoot() As Object Implements ICollection.SyncRoot
 Get
 Return Me
 End Get
 End Property
 ' IEnumerable Members
 Public Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
 ' Refer to the IEnumerator documentation for an example of
 ' implementing an enumerator.
 Throw New Exception("The method or operation is not implemented.")
 End Function
 Public Sub PrintContents(ByVal outputBlock As System.Windows.Controls.TextBlock)
 outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count) & vbCrLf
 outputBlock.Text &= "List contents:"
 Dim i As Integer
 For i = 0 To Count
 outputBlock.Text += String.Format(" {0}", _contents(i))
 Next i
 outputBlock.Text &= vbCrLf
 End Sub
End Class
' This code produces output similar to the following:
' Populate the List:
' List has a capacity of 8 and currently has 8 elements.
' List contents: one two three four five six seven eight
'
' Remove elements from the list:
' List has a capacity of 8 and currently has 6 elements.
' List contents: one two three four five seven
'
' Add an element to the end of the list:
' List has a capacity of 8 and currently has 7 elements.
' List contents: one two three four five seven nine
'
' Insert an element into the middle of the list:
' List has a capacity of 8 and currently has 8 elements.
' List contents: one two three four number five seven nine
'
' Check for specific elements in the list:
' List contains "three": True
' List contains "ten": False

using System;
using System.Collections;
class Example
{
 public static void Demo(System.Windows.Controls.TextBlock outputBlock)
 {
 SimpleList test = new SimpleList();
 // Populate the List
 outputBlock.Text += "Populate the List" + "\n";
 test.Add("one");
 test.Add("two");
 test.Add("three");
 test.Add("four");
 test.Add("five");
 test.Add("six");
 test.Add("seven");
 test.Add("eight");
 test.PrintContents(outputBlock);
 outputBlock.Text += "\n";
 // Remove elements from the list
 outputBlock.Text += "Remove elements from the list" + "\n";
 test.Remove("six");
 test.Remove("eight");
 test.PrintContents(outputBlock);
 outputBlock.Text += "\n";
 // Add an element to the end of the list
 outputBlock.Text += "Add an element to the end of the list" + "\n";
 test.Add("nine");
 test.PrintContents(outputBlock);
 outputBlock.Text += "\n";
 // Insert an element into the middle of the list
 outputBlock.Text += "Insert an element into the middle of the list" + "\n";
 test.Insert(4, "number");
 test.PrintContents(outputBlock);
 outputBlock.Text += "\n";
 // Check for specific elements in the list
 outputBlock.Text += "Check for specific elements in the list" + "\n";
 outputBlock.Text += String.Format("List contains \"three\": {0}", test.Contains("three")) + "\n";
 outputBlock.Text += String.Format("List contains \"ten\": {0}", test.Contains("ten")) + "\n";
 }
} // class Program
class SimpleList : IList
{
 private object[] _contents = new object[8];
 private int _count;
 public SimpleList()
 {
 _count = 0;
 }
 // IList Members
 public int Add(object value)
 {
 if (_count < _contents.Length)
 {
 _contents[_count] = value;
 _count++;
 return (_count - 1);
 }
 else
 {
 return -1;
 }
 }
 public void Clear()
 {
 _count = 0;
 }
 public bool Contains(object value)
 {
 bool inList = false;
 for (int i = 0; i < Count; i++)
 {
 if (_contents[i] == value)
 {
 inList = true;
 break;
 }
 }
 return inList;
 }
 public int IndexOf(object value)
 {
 int itemIndex = -1;
 for (int i = 0; i < Count; i++)
 {
 if (_contents[i] == value)
 {
 itemIndex = i;
 break;
 }
 }
 return itemIndex;
 }
 public void Insert(int index, object value)
 {
 if ((_count + 1 <= _contents.Length) && (index < Count) && (index >= 0))
 {
 _count++;
 for (int i = Count - 1; i > index; i--)
 {
 _contents[i] = _contents[i - 1];
 }
 _contents[index] = value;
 }
 }
 public bool IsFixedSize
 {
 get
 {
 return true;
 }
 }
 public bool IsReadOnly
 {
 get
 {
 return false;
 }
 }
 public void Remove(object value)
 {
 RemoveAt(IndexOf(value));
 }
 public void RemoveAt(int index)
 {
 if ((index >= 0) && (index < Count))
 {
 for (int i = index; i < Count - 1; i++)
 {
 _contents[i] = _contents[i + 1];
 }
 _count--;
 }
 }
 public object this[int index]
 {
 get
 {
 return _contents[index];
 }
 set
 {
 _contents[index] = value;
 }
 }
 // ICollection Members
 public void CopyTo(Array array, int index)
 {
 int j = index;
 for (int i = 0; i < Count; i++)
 {
 array.SetValue(_contents[i], j);
 j++;
 }
 }
 public int Count
 {
 get
 {
 return _count;
 }
 }
 public bool IsSynchronized
 {
 get
 {
 return false;
 }
 }
 // Return the current instance since the underlying store is not
 // publicly available.
 public object SyncRoot
 {
 get
 {
 return this;
 }
 }
 // IEnumerable Members
 public IEnumerator GetEnumerator()
 {
 // Refer to the IEnumerator documentation for an example of
 // implementing an enumerator.
 throw new Exception("The method or operation is not implemented.");
 }
 public void PrintContents(System.Windows.Controls.TextBlock outputBlock)
 {
 outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length, _count) + "\n";
 outputBlock.Text += "List contents:";
 for (int i = 0; i < Count; i++)
 {
 outputBlock.Text += String.Format(" {0}", _contents[i]);
 }
 outputBlock.Text += "\n";
 }
}
// This code produces output similar to the following:
// Populate the List:
// List has a capacity of 8 and currently has 8 elements.
// List contents: one two three four five six seven eight
//
// Remove elements from the list:
// List has a capacity of 8 and currently has 6 elements.
// List contents: one two three four five seven
//
// Add an element to the end of the list:
// List has a capacity of 8 and currently has 7 elements.
// List contents: one two three four five seven nine
//
// Insert an element into the middle of the list:
// List has a capacity of 8 and currently has 8 elements.
// List contents: one two three four number five seven nine
//
// Check for specific elements in the list:
// List contains "three": True
// List contains "ten": False

System.Collections Namespace

ICollection

System.Collections.Generic.IList<T>