ArrayList.ReadOnly Method

Reference

Definition

Namespace:: System.Collections

Assemblies:: mscorlib.dll, System.Collections.NonGeneric.dll

Assembly:: System.Runtime.dll

Assembly:: System.Collections.NonGeneric.dll

Assembly:: System.Runtime.Extensions.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Returns a list wrapper that is read-only.

Overloads

ReadOnly(ArrayList)	Returns a read-only ArrayList wrapper.
ReadOnly(IList)	Returns a read-only IList wrapper.

ReadOnly(ArrayList)

Source:: ArrayList.cs

Source:: ArrayList.cs

Source:: ArrayList.cs

Returns a read-only ArrayList wrapper.

public:
 static System::Collections::ArrayList ^ ReadOnly(System::Collections::ArrayList ^ list);

public static System.Collections.ArrayList ReadOnly (System.Collections.ArrayList list);

static member ReadOnly : System.Collections.ArrayList -> System.Collections.ArrayList

Public Shared Function ReadOnly (list As ArrayList) As ArrayList

Parameters

list: ArrayList

The ArrayList to wrap.

Returns

ArrayList

A read-only ArrayList wrapper around list.

Exceptions

ArgumentNullException

list is null.

Examples

The following code example shows how to create a read-only wrapper around an ArrayList and how to determine if an ArrayList is read-only.

#using <system.dll>

using namespace System;
using namespace System::Collections;
int main()
{
   
   // Creates and initializes a new ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "red" );
   myAL->Add( "orange" );
   myAL->Add( "yellow" );
   
   // Creates a read-only copy of the ArrayList.
   ArrayList^ myReadOnlyAL = ArrayList::ReadOnly( myAL );
   
   // Displays whether the ArrayList is read-only or writable.
   Console::WriteLine( "myAL is {0}.", myAL->IsReadOnly ? (String^)"read-only" : "writable" );
   Console::WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL->IsReadOnly ? (String^)"read-only" : "writable" );
   
   // Displays the contents of both collections.
   Console::WriteLine( "\nInitially," );
   Console::WriteLine( "The original ArrayList myAL contains:" );
   for ( int i(0); i < myAL->Count; ++i )
      Console::WriteLine(  "   {0}", static_cast<String^>(myAL[ i ]) );
   Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
   for ( int i(0); i < myReadOnlyAL->Count; ++i )
      Console::WriteLine( "   {0}", static_cast<String^>(myReadOnlyAL[ i ]) );
   
   // Adding an element to a read-only ArrayList throws an exception.
   Console::WriteLine( "\nTrying to add a new element to the read-only ArrayList:" );
   try
   {
      myReadOnlyAL->Add( "green" );
   }
   catch ( Exception^ myException ) 
   {
      Console::WriteLine( String::Concat( "Exception: ", myException->ToString() ) );
   }

   
   // Adding an element to the original ArrayList affects the read-only ArrayList.
   myAL->Add( "blue" );
   
   // Displays the contents of both collections again.
   Console::WriteLine( "\nAfter adding a new element to the original ArrayList," );
   Console::WriteLine( "The original ArrayList myAL contains:" );
   for ( int i(0); i < myAL->Count; ++i )
      Console::WriteLine( "   {0}", static_cast<String^>(myAL[ i ]) );
   Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
   for ( int i(0); i < myReadOnlyAL->Count; ++i )
      Console::WriteLine( "   {0}", static_cast<String^>(myReadOnlyAL[ i ]) );
}

/*
This code produces the following output.

myAL is writable.
myReadOnlyAL is read-only.

Initially,
The original ArrayList myAL contains:
   red
   orange
   yellow
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow

Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
   at System.Collections.ReadOnlyArrayList.Add(Object obj)
   at SamplesArrayList.Main()

After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
   red
   orange
   yellow
   blue
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow
   blue

*/

 using System;
 using System.Collections;
 public class SamplesArrayList  {

    public static void Main()  {

       // Creates and initializes a new ArrayList.
       ArrayList myAL = new ArrayList();
       myAL.Add( "red" );
       myAL.Add( "orange" );
       myAL.Add( "yellow" );

       // Creates a read-only copy of the ArrayList.
       ArrayList myReadOnlyAL = ArrayList.ReadOnly( myAL );

       // Displays whether the ArrayList is read-only or writable.
       Console.WriteLine( "myAL is {0}.", myAL.IsReadOnly ? "read-only" : "writable" );
       Console.WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL.IsReadOnly ? "read-only" : "writable" );

       // Displays the contents of both collections.
       Console.WriteLine( "\nInitially," );
       Console.WriteLine( "The original ArrayList myAL contains:" );
       foreach ( string myStr in myAL )
          Console.WriteLine( "   {0}", myStr );
       Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
       foreach ( string myStr in myReadOnlyAL )
          Console.WriteLine( "   {0}", myStr );

       // Adding an element to a read-only ArrayList throws an exception.
       Console.WriteLine( "\nTrying to add a new element to the read-only ArrayList:" );
       try  {
          myReadOnlyAL.Add("green");
       } catch ( Exception myException )  {
          Console.WriteLine("Exception: " + myException.ToString());
       }

       // Adding an element to the original ArrayList affects the read-only ArrayList.
       myAL.Add( "blue" );

       // Displays the contents of both collections again.
       Console.WriteLine( "\nAfter adding a new element to the original ArrayList," );
       Console.WriteLine( "The original ArrayList myAL contains:" );
       foreach ( string myStr in myAL )
          Console.WriteLine( "   {0}", myStr );
       Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:" );
       foreach ( string myStr in myReadOnlyAL )
          Console.WriteLine( "   {0}", myStr );
    }
 }


/*
This code produces the following output.

myAL is writable.
myReadOnlyAL is read-only.

Initially,
The original ArrayList myAL contains:
   red
   orange
   yellow
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow

Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
   at System.Collections.ReadOnlyArrayList.Add(Object obj)
   at SamplesArrayList.Main()

After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
   red
   orange
   yellow
   blue
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow
   blue

*/

Imports System.Collections

Public Class SamplesArrayList

   Public Shared Sub Main()

      Dim myStr As [String]

      ' Creates and initializes a new ArrayList.
      Dim myAL As New ArrayList()
      myAL.Add("red")
      myAL.Add("orange")
      myAL.Add("yellow")

      ' Creates a read-only copy of the ArrayList.
      Dim myReadOnlyAL As ArrayList = ArrayList.ReadOnly(myAL)

      ' Displays whether the ArrayList is read-only or writable.
      If myAL.IsReadOnly Then
         Console.WriteLine("myAL is read-only.")
      Else
         Console.WriteLine("myAL is writable.")
      End If
      If myReadOnlyAL.IsReadOnly Then
         Console.WriteLine("myReadOnlyAL is read-only.")
      Else
         Console.WriteLine("myReadOnlyAL is writable.")
      End If

      ' Displays the contents of both collections.
      Console.WriteLine()
      Console.WriteLine("Initially,")
      Console.WriteLine("The original ArrayList myAL contains:")
      For Each myStr In  myAL
         Console.WriteLine("   {0}", myStr)
      Next myStr
      Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:")
      For Each myStr In  myReadOnlyAL
         Console.WriteLine("   {0}", myStr)
      Next myStr 

      ' Adding an element to a read-only ArrayList throws an exception.
      Console.WriteLine()
      Console.WriteLine("Trying to add a new element to the read-only ArrayList:")
      Try
         myReadOnlyAL.Add("green")
      Catch myException As Exception
         Console.WriteLine(("Exception: " + myException.ToString()))
      End Try

      ' Adding an element to the original ArrayList affects the read-only ArrayList.
      myAL.Add("blue")

      ' Displays the contents of both collections again.
      Console.WriteLine()
      Console.WriteLine("After adding a new element to the original ArrayList,")
      Console.WriteLine("The original ArrayList myAL contains:")
      For Each myStr In  myAL
         Console.WriteLine("   {0}", myStr)
      Next myStr
      Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:")
      For Each myStr In  myReadOnlyAL
         Console.WriteLine("   {0}", myStr)
      Next myStr 

   End Sub

End Class


'This code produces the following output.
'
'myAL is writable.
'myReadOnlyAL is read-only.
'
'Initially,
'The original ArrayList myAL contains:
'   red
'   orange
'   yellow
'The read-only ArrayList myReadOnlyAL contains:
'   red
'   orange
'   yellow
'
'Trying to add a new element to the read-only ArrayList:
'Exception: System.NotSupportedException: Collection is read-only.
'   at System.Collections.ReadOnlyArrayList.Add(Object obj)
'   at SamplesArrayList.Main()
'
'After adding a new element to the original ArrayList,
'The original ArrayList myAL contains:
'   red
'   orange
'   yellow
'   blue
'The read-only ArrayList myReadOnlyAL contains:
'   red
'   orange
'   yellow
'   blue

Remarks

To prevent any modifications to list, expose list only through this wrapper.

A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection. If changes are made to the underlying collection, the read-only collection reflects those changes.

This method is an O(1) operation.

Applies to

ReadOnly(IList)

Source:: ArrayList.cs

Source:: ArrayList.cs

Source:: ArrayList.cs

Returns a read-only IList wrapper.

public:
 static System::Collections::IList ^ ReadOnly(System::Collections::IList ^ list);

public static System.Collections.IList ReadOnly (System.Collections.IList list);

static member ReadOnly : System.Collections.IList -> System.Collections.IList

Public Shared Function ReadOnly (list As IList) As IList

Parameters

list: IList

The IList to wrap.

Returns

IList

A read-only IList wrapper around list.

Exceptions

ArgumentNullException

list is null.

Remarks

To prevent any modifications to list, expose list only through this wrapper.

This method is an O(1) operation.

Applies to

Share via

ArrayList.ReadOnly Method

Definition

Overloads

ReadOnly(ArrayList)

Parameters

Returns

Exceptions

Examples

Remarks

See also

Applies to

ReadOnly(IList)

Parameters

Returns

Exceptions

Remarks

See also

Applies to

Additional resources