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.
#using <System.dll> using namespace System; using namespace System::Collections; using namespace System::Collections::Specialized; public ref class MyCollection : public NameObjectCollectionBase { private: DictionaryEntry^ _de; // Gets a key-and-value pair (DictionaryEntry) using an index. public: property DictionaryEntry^ default[ int ] { DictionaryEntry^ get( 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 ) { _de = gcnew DictionaryEntry(); for each ( DictionaryEntry^ de in d ) { this->BaseAdd( (String^) de->Key, de->Value ); } this->IsReadOnly = bReadOnly; } // Adds an entry to the collection. void Add( String^ key, Object^ value ) { this->BaseAdd( key, value ); } }; public ref class SamplesNameObjectCollectionBase { public: static void Main() { // Creates and initializes a new MyCollection that is read-only. IDictionary^ d = gcnew ListDictionary(); d->Add( "red", "apple" ); d->Add( "yellow", "banana" ); d->Add( "green", "pear" ); MyCollection^ myROCol = gcnew 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 ); } 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 ); } } }; int main() { SamplesNameObjectCollectionBase::Main(); } /* 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 */
Available since 10
.NET Framework
Available since 1.1