IList Interface
 
System_CAPS_noteNote

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

Namespace:   System.Collections
Assembly:  mscorlib (in mscorlib.dll)

[ComVisibleAttribute(true)]
public interface IList : ICollection, IEnumerable
[ComVisibleAttribute(true)]
public interface class IList : ICollection, IEnumerable
[<ComVisibleAttribute(true)>]
type IList = 
    interface
        interface ICollection
        interface IEnumerable
    end
<ComVisibleAttribute(True)>
Public Interface IList
	Inherits ICollection, IEnumerable
NameDescription
System_CAPS_pubproperty

Gets the number of elements contained in the ICollection.(Inherited from ICollection.)

System_CAPS_pubproperty

Gets a value indicating whether the IList has a fixed size.

System_CAPS_pubproperty

Gets a value indicating whether the IList is read-only.

System_CAPS_pubproperty

Gets a value indicating whether access to the ICollection is synchronized (thread safe).(Inherited from ICollection.)

System_CAPS_pubproperty

Gets or sets the element at the specified index.

System_CAPS_pubproperty

Gets an object that can be used to synchronize access to the ICollection.(Inherited from ICollection.)

NameDescription
System_CAPS_pubmethod Add

Adds an item to the IList.

System_CAPS_pubmethod Clear

Removes all items from the IList.

System_CAPS_pubmethod Contains

Determines whether the IList contains a specific value.

System_CAPS_pubmethod CopyTo

Copies the elements of the ICollection to an Array, starting at a particular Array index.(Inherited from ICollection.)

System_CAPS_pubmethod GetEnumerator

Returns an enumerator that iterates through a collection.(Inherited from IEnumerable.)

System_CAPS_pubmethod IndexOf

Determines the index of a specific item in the IList.

System_CAPS_pubmethod Insert

Inserts an item to the IList at the specified index.

System_CAPS_pubmethod Remove

Removes the first occurrence of a specific object from the IList.

System_CAPS_pubmethod RemoveAt

Removes the IList item at the specified index.

NameDescription
System_CAPS_pubmethod AsParallel

Overloaded. Enables parallelization of a query.(Defined by ParallelEnumerable.)

System_CAPS_pubmethod AsQueryable

Overloaded. Converts an IEnumerable to an IQueryable.(Defined by Queryable.)

System_CAPS_pubmethod Cast

Casts the elements of an IEnumerable to the specified type.(Defined by Enumerable.)

System_CAPS_pubmethod OfType

Filters the elements of an IEnumerable based on a specified type.(Defined by Enumerable.)

IList is a descendant of the ICollection interface and is the base interface of all non-generic lists. IList implementations fall into three categories: read-only, fixed-size, and variable-size. A read-only IList cannot be modified. A fixed-size IList does not allow the addition or removal of elements, but it allows the modification of existing elements. A variable-size IList allows the addition, removal, and modification of elements.

For the generic version of this interface, see System.Collections.GenericIList.

The following example demonstrates the implementation of the IList interface to create a simple list, fixed-size list.

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        SimpleList test = new SimpleList();

        // Populate the List
        Console.WriteLine("Populate the List");
        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();
        Console.WriteLine();

        // Remove elements from the list
        Console.WriteLine("Remove elements from the list");
        test.Remove("six");
        test.Remove("eight");
        test.PrintContents();
        Console.WriteLine();

        // Add an element to the end of the list
        Console.WriteLine("Add an element to the end of the list");
        test.Add("nine");
        test.PrintContents();
        Console.WriteLine();

        // Insert an element into the middle of the list
        Console.WriteLine("Insert an element into the middle of the list");
        test.Insert(4, "number");
        test.PrintContents();
        Console.WriteLine();

        // Check for specific elements in the list
        Console.WriteLine("Check for specific elements in the list");
        Console.WriteLine("List contains \"three\": {0}", test.Contains("three"));
        Console.WriteLine("List contains \"ten\": {0}", test.Contains("ten"));
    }
} // 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()
    {
        Console.WriteLine("List has a capacity of {0} and currently has {1} elements.", _contents.Length, _count);
        Console.Write("List contents:");
        for (int i = 0; i < Count; i++)
        {
            Console.Write(" {0}", _contents[i]);
        }
        Console.WriteLine();
    }
}

// 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
Imports System
Imports System.Collections

Public Class Program

    Shared Sub Main()

        Dim myList As New SimpleList()

        ' Populate the List
        Console.WriteLine("Populate the List")
        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()
        Console.WriteLine()

        ' Remove elements from the list
        Console.WriteLine("Remove elements from the list")
        myList.Remove("six")
        myList.Remove("eight")
        myList.PrintContents()
        Console.WriteLine()

        ' Add an element to the end of the list
        Console.WriteLine("Add an element to the end of the list")
        myList.Add("nine")
        myList.PrintContents()
        Console.WriteLine()

        ' Insert an element into the middle of the list
        Console.WriteLine("Insert an element into the middle of the list")
        myList.Insert(4, "number")
        myList.PrintContents()
        Console.WriteLine()

        ' Check for specific elements in the list
        Console.WriteLine("Check for specific elements in the list")
        Console.WriteLine("List contains 'three': {0}", myList.Contains("three"))
        Console.WriteLine("List contains 'ten': {0}", myList.Contains("ten"))

    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()

        Console.WriteLine("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count)
        Console.Write("List contents:")

        Dim i As Integer
        For i = 0 To Count

            Console.Write(" {0}", _contents(i))
        Next i

        Console.WriteLine()

    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
Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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