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ReadOnlyCollection(Of T).Contains Method

Determines whether an element is in the ReadOnlyCollection(Of T).

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

Public Function Contains ( _
	value As T _
) As Boolean
Dim instance As ReadOnlyCollection 
Dim value As T
Dim returnValue As Boolean 

returnValue = instance.Contains(value)


Type: T

The object to locate in the ReadOnlyCollection(Of T). The value can be Nothing for reference types.

Return Value

Type: System.Boolean
true if value is found in the ReadOnlyCollection(Of T); otherwise, false.


ICollection(Of T).Contains(T)

This method determines equality using the default equality comparer EqualityComparer(Of T).Default.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

The following code example demonstrates several members of the ReadOnlyCollection(Of T) class. The code example creates a List(Of T) of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection(Of T).

After demonstrating the Count, Contains, Item, and IList.IndexOf members, the code example shows that the ReadOnlyCollection(Of T) is just a wrapper for the original List(Of T) by adding a new item to the List(Of T) and displaying the contents of the ReadOnlyCollection(Of T).

Finally, the code example creates an array larger than the collection and uses the CopyTo method to insert the elements of the collection into the middle of the array.

Imports System
Imports System.Collections.Generic
Imports System.Collections.ObjectModel

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)


        Dim readOnlyDinosaurs As _
            New ReadOnlyCollection(Of String)(dinosaurs)

        For Each dinosaur As String In readOnlyDinosaurs

        Console.WriteLine(vbLf & "Count: {0}", _

        Console.WriteLine(vbLf & "Contains(""Deinonychus""): {0}", _

        Console.WriteLine(vbLf & _
            "readOnlyDinosaurs(3): {0}", readOnlyDinosaurs(3))

        Console.WriteLine(vbLf & "IndexOf(""Compsognathus""): {0}", _

        Console.WriteLine(vbLf & "Insert into the wrapped List:")
        Console.WriteLine("Insert(2, ""Oviraptor"")")
        dinosaurs.Insert(2, "Oviraptor")

        For Each dinosaur As String In readOnlyDinosaurs

        Dim dinoArray(readOnlyDinosaurs.Count + 1) As String
        readOnlyDinosaurs.CopyTo(dinoArray, 1)

        Console.WriteLine(vbLf & "Copied array has {0} elements:", _
        For Each dinosaur As String In dinoArray
            Console.WriteLine("""{0}""", dinosaur)

   End Sub 
End Class 

' This code example produces the following output: 


'Count: 4 

'Contains("Deinonychus"): True 

'readOnlyDinosaurs(3): Compsognathus 

'IndexOf("Compsognathus"): 3 

'Insert into the wrapped List: 
'Insert(2, "Oviraptor") 


'Copied array has 7 elements: 

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0