NameObjectCollectionBase.IsReadOnly Property
Gets or sets a value indicating whether the NameObjectCollectionBase instance is read-only.
[Visual Basic] Protected Property IsReadOnly As Boolean [C#] protected bool IsReadOnly {get; set;} [C++] protected: __property bool get_IsReadOnly(); protected: __property void set_IsReadOnly(bool); [JScript] protected function get IsReadOnly() : Boolean; protected function set IsReadOnly(Boolean);
Property Value
true if the NameObjectCollectionBase instance 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.
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.
Example
[Visual Basic, C#, C++] The following code example creates a read-only collection.
[Visual Basic] 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 [C#] using System; using System.Collections; using System.Collections.Specialized; public class MyCollection : NameObjectCollectionBase { private DictionaryEntry _de = new DictionaryEntry(); // Gets a key-and-value pair (DictionaryEntry) using an index. public DictionaryEntry this[ int index ] { get { _de.Key = this.BaseGetKey( index ); _de.Value = this.BaseGet( index ); return( _de ); } } // Adds elements from an IDictionary into the new collection. public MyCollection( IDictionary d, Boolean bReadOnly ) { foreach ( DictionaryEntry de in d ) { this.BaseAdd( (String) de.Key, de.Value ); } this.IsReadOnly = bReadOnly; } // Adds an entry to the collection. public void Add( String key, Object value ) { this.BaseAdd( key, value ); } } public class SamplesNameObjectCollectionBase { public static void Main() { // Creates and initializes a new MyCollection that is read-only. IDictionary d = new ListDictionary(); d.Add( "red", "apple" ); d.Add( "yellow", "banana" ); d.Add( "green", "pear" ); MyCollection myROCol = new MyCollection( d, true ); // Tries to add a new item. try { myROCol.Add( "blue", "sky" ); } catch ( NotSupportedException e ) { Console.WriteLine( e.ToString() ); } // Displays the keys and values of the MyCollection. Console.WriteLine( "Read-Only Collection:" ); PrintKeysAndValues( myROCol ); } public static void PrintKeysAndValues( MyCollection myCol ) { for ( int i = 0; i < myCol.Count; i++ ) { Console.WriteLine( "[{0}] : {1}, {2}", i, myCol[i].Key, myCol[i].Value ); } } } /* 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 */ [C++] #using <mscorlib.dll> #using <system.dll> using namespace System; using namespace System::Collections; using namespace System::Collections::Specialized; public __gc class MyCollection : public NameObjectCollectionBase { private: DictionaryEntry _de; public: // Gets a key-and-value pair (DictionaryEntry) using an index. __property DictionaryEntry get_Item( int index ) { _de.Key = this->BaseGetKey(index); _de.Value = this->BaseGet(index); return(_de); } // Adds elements from an IDictionary into the new collection. MyCollection(IDictionary* d, Boolean bReadOnly) { IEnumerator* myEnum = d->GetEnumerator(); while (myEnum->MoveNext()) { DictionaryEntry* de = __try_cast<DictionaryEntry*>(myEnum->Current); this->BaseAdd(__try_cast<String*>(de->Key), de->Value); } this->IsReadOnly = bReadOnly; } // Adds an entry to the collection. void Add(String* key, Object* value) { this->BaseAdd(key, value); } }; void PrintKeysAndValues(MyCollection* myCol) { for (int i = 0; i < myCol->Count; i++) { Console::WriteLine(S"[{0}] : {1}, {2}", __box(i), myCol->Item[i].Key, myCol->Item[i].Value); } } int main() { // Creates and initializes a new MyCollection that is read-only. IDictionary* d = new ListDictionary(); d->Add(S"red", S"apple"); d->Add(S"yellow", S"banana"); d->Add(S"green", S"pear"); MyCollection* myROCol = new MyCollection(d, true); // Tries to add a new item. try { myROCol->Add(S"blue", S"sky"); } catch (NotSupportedException* e) { Console::WriteLine(e); } // Displays the keys and values of the MyCollection. Console::WriteLine(S"Read-Only Collection:"); PrintKeysAndValues(myROCol); } /* This code produces the following output. System.NotSupportedException: Collection is read-only. at System.Collections.Specialized.NameObjectCollectionBase.BaseAdd(String name, Object value) at main() Read-Only Collection: [0] : red, apple [1] : yellow, banana [2] : green, pear */
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Requirements
Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework
See Also
NameObjectCollectionBase Class | NameObjectCollectionBase Members | System.Collections.Specialized Namespace