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IList Interface

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

The IList type exposes the following members.

  NameDescription
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCountGets the number of elements contained in the ICollection. (Inherited from ICollection.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsFixedSizeGets a value indicating whether the IList has a fixed size.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsReadOnlyGets a value indicating whether the IList is read-only.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsItemGets or sets the element at the specified index.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsSyncRootGets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.)
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  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsAddAdds an item to the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsClearRemoves all items from the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsContainsDetermines whether the IList contains a specific value.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCopyToCopies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetEnumeratorReturns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIndexOfDetermines the index of a specific item in the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsInsertInserts an item to the IList at the specified index.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveRemoves the first occurrence of a specific object from the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveAtRemoves the IList item at the specified index.
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  NameDescription
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsParallelEnables parallelization of a query. (Defined by ParallelEnumerable.)
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCast<TResult>Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsOfType<TResult>Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
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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.Generic.IList<T>.

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

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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