NameObjectCollectionBase.IsReadOnly Property
.NET Framework (current version)
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; 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 */
Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 10
.NET Framework
Available since 1.1
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