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NameObjectCollectionBase.IsReadOnly Property

Gets or sets a value indicating whether the NameObjectCollectionBase instance is read-only.

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

'Declaration
Protected Property IsReadOnly As Boolean

Property Value

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

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

A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection; therefore, if changes are made to the underlying collection, the read-only collection reflects those changes.

Retrieving the value of this property is an O(1) operation.

The following code example creates a read-only collection.

Imports System
Imports System.Collections
Imports System.Collections.Specialized

Public Class MyCollection
   Inherits NameObjectCollectionBase

   Private _de As New DictionaryEntry()

   ' Gets a key-and-value pair (DictionaryEntry) using an index. 
   Default Public ReadOnly Property Item(index As Integer) As DictionaryEntry
      Get
         _de.Key = Me.BaseGetKey(index)
         _de.Value = Me.BaseGet(index)
         Return _de
      End Get 
   End Property 

   ' Adds elements from an IDictionary into the new collection. 
   Public Sub New(d As IDictionary, bReadOnly As [Boolean])
      Dim de As DictionaryEntry
      For Each de In  d
         Me.BaseAdd(CType(de.Key, [String]), de.Value)
      Next de
      Me.IsReadOnly = bReadOnly
   End Sub 'New 

   ' Adds an entry to the collection. 
   Public Sub Add(key As [String], value As [Object])
      Me.BaseAdd(key, value)
   End Sub 'Add

End Class 'MyCollection


Public Class SamplesNameObjectCollectionBase   

   Public Shared Sub Main()

      ' Creates and initializes a new MyCollection that is read-only. 
      Dim d = New ListDictionary()
      d.Add("red", "apple")
      d.Add("yellow", "banana")
      d.Add("green", "pear")
      Dim myROCol As New MyCollection(d, True)

      ' Tries to add a new item. 
      Try
         myROCol.Add("blue", "sky")
      Catch e As NotSupportedException
         Console.WriteLine(e.ToString())
      End Try 

      ' Displays the keys and values of the MyCollection.
      Console.WriteLine("Read-Only Collection:")
      PrintKeysAndValues(myROCol)

   End Sub 'Main

   Public Shared Sub PrintKeysAndValues(myCol As MyCollection)
      Dim i As Integer 
      For i = 0 To myCol.Count - 1
         Console.WriteLine("[{0}] : {1}, {2}", i, myCol(i).Key, myCol(i).Value)
      Next i
   End Sub 'PrintKeysAndValues

End Class 'SamplesNameObjectCollectionBase 


'This code produces the following output. 

'System.NotSupportedException: Collection is read-only. 
'   at System.Collections.Specialized.NameObjectCollectionBase.BaseAdd(String name, Object value) 
'   at SamplesNameObjectCollectionBase.Main() 
'Read-Only Collection: 
'[0] : red, apple 
'[1] : yellow, banana 
'[2] : green, pear

.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

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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