IList Interface
Represents a non-generic collection of objects that can be individually accessed by index.
Assembly: mscorlib (in mscorlib.dll)
The IList type exposes the following members.
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Count | Gets the number of elements contained in the ICollection. (Inherited from ICollection.) |
![]() ![]() ![]() | IsFixedSize | Gets a value indicating whether the IList has a fixed size. |
![]() ![]() ![]() | IsReadOnly | Gets a value indicating whether the IList is read-only. |
![]() ![]() ![]() | IsSynchronized | Gets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.) |
![]() ![]() ![]() | Item | Gets or sets the element at the specified index. |
![]() ![]() ![]() | SyncRoot | Gets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.) |
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Add | Adds an item to the IList. |
![]() ![]() ![]() | Clear | Removes all items from the IList. |
![]() ![]() ![]() | Contains | Determines whether the IList contains a specific value. |
![]() ![]() ![]() | CopyTo | Copies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.) |
![]() ![]() ![]() | GetEnumerator | Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.) |
![]() ![]() ![]() | IndexOf | Determines the index of a specific item in the IList. |
![]() ![]() ![]() | Insert | Inserts an item to the IList at the specified index. |
![]() ![]() ![]() | Remove | Removes the first occurrence of a specific object from the IList. |
![]() ![]() ![]() | RemoveAt | Removes the IList item at the specified index. |
| Name | Description | |
|---|---|---|
![]() | AsParallel | Enables parallelization of a query. (Defined by ParallelEnumerable.) |
![]() ![]() | AsQueryable | Converts an IEnumerable to an IQueryable. (Defined by Queryable.) |
![]() ![]() ![]() | Cast<TResult> | Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.) |
![]() ![]() ![]() | OfType<TResult> | 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.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
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

