ArrayList.IsReadOnly Property
Definition
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.
Gets a value indicating whether the ArrayList is read-only.
public:
virtual property bool IsReadOnly { bool get(); };public virtual bool IsReadOnly { get; }member this.IsReadOnly : boolPublic Overridable ReadOnly Property IsReadOnly As BooleanProperty Value
true if the ArrayList is read-only; otherwise, false. The default is false.
Implements
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;
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
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.
