Export (0) Print
Expand All

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
*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

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

Show:
© 2015 Microsoft