ArrayList.ReadOnly Method
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Returns a list wrapper that is read-only.
| ReadOnly(ArrayList) |
Returns a read-only ArrayList wrapper. |
| ReadOnly(IList) |
Returns a read-only IList wrapper. |
- 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);C#
public static System.Collections.ArrayList ReadOnly(System.Collections.ArrayList list);static member ReadOnly : System.Collections.ArrayList -> System.Collections.ArrayListPublic Shared Function ReadOnly (list As ArrayList) As ArrayListParameters
Returns
A read-only ArrayList wrapper around list.
Exceptions
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
*/
C#
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.
See also
Applies to
.NET 10 and other versions
| Product | Versions |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9, 10 |
| .NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 2.0, 2.1 |
| UWP | 10.0 |
- 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);C#
public static System.Collections.IList ReadOnly(System.Collections.IList list);static member ReadOnly : System.Collections.IList -> System.Collections.IListPublic Shared Function ReadOnly (list As IList) As IListParameters
Returns
A read-only IList wrapper around list.
Exceptions
list is null.
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.
See also
Applies to
.NET 10 and other versions
| Product | Versions |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9, 10 |
| .NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 2.0, 2.1 |
| UWP | 10.0 |
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