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IList Interface

Silverlight

Other Versions

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

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

Syntax

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[ComVisibleAttribute(true)]
[DefaultMemberAttribute("Item")]
public interface IList : ICollection, IEnumerable

The IList type exposes the following members.

Properties

	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.)

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Methods

	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.

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Extension Methods

	Name	Description
	AsQueryable	Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
	Cast<TResult>	Converts 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.)

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Remarks

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>.

Examples

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

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.

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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