IList Interface

July 28, 2014

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

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

public interface IList : ICollection, IEnumerable

The IList type exposes the following members.

  NameDescription
Public propertyCountGets the number of elements contained in the ICollection. (Inherited from ICollection.)
Public propertyIsFixedSizeGets a value indicating whether the IList has a fixed size.
Public propertyIsReadOnlyGets a value indicating whether the IList is read-only.
Public propertyIsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.)
Public propertyItemGets or sets the element at the specified index.
Public propertySyncRootGets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.)
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  NameDescription
Public methodAddAdds an item to the IList.
Public methodClearRemoves all items from the IList.
Public methodContainsDetermines whether the IList contains a specific value.
Public methodCopyToCopies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.)
Public methodGetEnumeratorReturns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
Public methodIndexOfDetermines the index of a specific item in the IList.
Public methodInsertInserts an item to the IList at the specified index.
Public methodRemoveRemoves the first occurrence of a specific object from the IList.
Public methodRemoveAtRemoves the IList item at the specified index.
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  NameDescription
Public Extension MethodAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodCast<TResult>Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodOfType<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 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


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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