IList.IsReadOnly Property

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

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

Syntax

'Declaration
ReadOnly Property IsReadOnly As Boolean
bool IsReadOnly { get; }

Property Value

Type: System.Boolean
true if the IList is read-only; otherwise, false.

Remarks

A collection that is read-only does not allow the addition, removal, or modification of elements after the collection is created.

Examples

The following example demonstrates the implementation of the IList interface to create a simple list, fixed-size list. This code is part of a larger example for the IList interface.

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(ByVal outputBlock As System.Windows.Controls.TextBlock)

      outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count) & vbCrLf
      outputBlock.Text &= "List contents:"

      Dim i As Integer
      For i = 0 To Count

         outputBlock.Text += String.Format(" {0}", _contents(i))
      Next i

      outputBlock.Text &= vbCrLf

   End Sub
End Class
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";
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.