NameObjectCollectionBase.IsReadOnly Property
Gets or sets a value indicating whether the NameObjectCollectionBase instance is read-only.
Assembly: System (in System.dll)
Property Value
Type: System.Booleantrue 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
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.