List(T).AsReadOnly Method

Returns a read-only IList(T) wrapper for the current collection.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

member AsReadOnly : unit -> ReadOnlyCollection<'T> 

Return Value

Type: System.Collections.ObjectModel.ReadOnlyCollection(T)
A ReadOnlyCollection(T) that acts as a read-only wrapper around the current List(T).

To prevent any modifications to List(T), expose List(T) only through this wrapper. A ReadOnlyCollection(T) does not expose methods that modify the collection. However, if changes are made to the underlying List(T), the read-only collection reflects those changes.

This method is an O(1) operation.

The following example demonstrates the AsReadOnly method. A List(T) of strings with a capacity of 4 is created, because the ultimate size of the list is known to be exactly 4. The list is populated with four strings, and the AsReadOnly method is used to get a read-only IList(T) generic interface implementation that wraps the original list.

An element of the original list is set to "Coelophysis" using the Item property (the indexer in C#), and the contents of the read-only list are displayed again to demonstrate that it is just a wrapper for the original list.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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