ReadOnlyCollection<T>.Contains Method
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Determines whether an element is in the ReadOnlyCollection<T>.
Namespace: System.Collections.ObjectModel
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Function Contains ( _
value As T _
) As Boolean
public bool Contains(
T value
)
Parameters
- value
Type: T
The object to locate in the ReadOnlyCollection<T>. The value can be nulla null reference (Nothing in Visual Basic) for reference types.
Return Value
Type: System.Boolean
true if value is found in the ReadOnlyCollection<T>; otherwise, false.
Implements
Remarks
This method determines equality using the default equality comparer EqualityComparer<T>.Default.
This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.
Examples
The following code example demonstrates several members of the ReadOnlyCollection<T> class. The code example creates a List<T> of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection<T>.
After demonstrating the Count, Contains, Item, and IList.IndexOf members, the code example shows that the ReadOnlyCollection<T> is just a wrapper for the original List<T> by adding a new item to the List<T> and displaying the contents of the ReadOnlyCollection<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.Collections.Generic
Imports System.Collections.ObjectModel
Public Class Example
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim dinosaurs As New List(Of String)
dinosaurs.Add("Tyrannosaurus")
dinosaurs.Add("Amargasaurus")
dinosaurs.Add("Deinonychus")
dinosaurs.Add("Compsognathus")
Dim readOnlyDinosaurs As _
New ReadOnlyCollection(Of String)(dinosaurs)
outputBlock.Text &= vbCrLf
For Each dinosaur As String In readOnlyDinosaurs
outputBlock.Text &= dinosaur & vbCrLf
Next
outputBlock.Text &= String.Format(vbLf & "Count: {0}", _
readOnlyDinosaurs.Count) & vbCrLf
outputBlock.Text &= String.Format(vbLf & "Contains(""Deinonychus"" & vbCrLf: {0}", _
readOnlyDinosaurs.Contains("Deinonychus"))
outputBlock.Text &= String.Format(vbLf & _
"readOnlyDinosaurs(3): {0}", readOnlyDinosaurs(3)) & vbCrLf
outputBlock.Text &= String.Format(vbLf & "IndexOf(""Compsognathus"" & vbCrLf: {0}", _
readOnlyDinosaurs.IndexOf("Compsognathus"))
outputBlock.Text &= vbLf & "Insert into the wrapped List:" & vbCrLf
outputBlock.Text &= String.Format("Insert(2, ""Oviraptor"")") & vbCrLf
dinosaurs.Insert(2, "Oviraptor")
outputBlock.Text &= vbCrLf
For Each dinosaur As String In readOnlyDinosaurs
outputBlock.Text &= dinosaur & vbCrLf
Next
Dim dinoArray(readOnlyDinosaurs.Count + 1) As String
readOnlyDinosaurs.CopyTo(dinoArray, 1)
outputBlock.Text &= String.Format(vbLf & "Copied array has {0} elements:", _
dinoArray.Length) & vbCrLf
For Each dinosaur As String In dinoArray
outputBlock.Text &= String.Format("""{0}""", dinosaur) & vbCrLf
Next
End Sub
End Class
' This code example produces the following output:
'
'Tyrannosaurus
'Amargasaurus
'Deinonychus
'Compsognathus
'
'Count: 4
'
'Contains("Deinonychus"): True
'
'readOnlyDinosaurs(3): Compsognathus
'
'IndexOf("Compsognathus"): 3
'
'Insert into the wrapped List:
'Insert(2, "Oviraptor")
'
'Tyrannosaurus
'Amargasaurus
'Oviraptor
'Deinonychus
'Compsognathus
'
'Copied array has 7 elements:
'""
'"Tyrannosaurus"
'"Amargasaurus"
'"Oviraptor"
'"Deinonychus"
'"Compsognathus"
'""
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
List<string> dinosaurs = new List<string>();
dinosaurs.Add("Tyrannosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("Deinonychus");
dinosaurs.Add("Compsognathus");
ReadOnlyCollection<string> readOnlyDinosaurs =
new ReadOnlyCollection<string>(dinosaurs);
outputBlock.Text += "\n";
foreach (string dinosaur in readOnlyDinosaurs)
{
outputBlock.Text += dinosaur + "\n";
}
outputBlock.Text += String.Format("\nCount: {0}", readOnlyDinosaurs.Count) + "\n";
outputBlock.Text += String.Format("\nContains(\"Deinonychus\"): {0}",
readOnlyDinosaurs.Contains("Deinonychus")) + "\n";
outputBlock.Text += String.Format("\nreadOnlyDinosaurs[3]: {0}",
readOnlyDinosaurs[3]) + "\n";
outputBlock.Text += String.Format("\nIndexOf(\"Compsognathus\"): {0}",
readOnlyDinosaurs.IndexOf("Compsognathus")) + "\n";
outputBlock.Text += "\nInsert into the wrapped List:" + "\n";
outputBlock.Text += String.Format("Insert(2, \"Oviraptor\")") + "\n";
dinosaurs.Insert(2, "Oviraptor");
outputBlock.Text += "\n";
foreach (string dinosaur in readOnlyDinosaurs)
{
outputBlock.Text += dinosaur + "\n";
}
string[] dinoArray = new string[readOnlyDinosaurs.Count + 2];
readOnlyDinosaurs.CopyTo(dinoArray, 1);
outputBlock.Text += String.Format("\nCopied array has {0} elements:",
dinoArray.Length) + "\n";
foreach (string dinosaur in dinoArray)
{
outputBlock.Text += String.Format("\"{0}\"", dinosaur) + "\n";
}
}
}
/* This code example produces the following output:
Tyrannosaurus
Amargasaurus
Deinonychus
Compsognathus
Count: 4
Contains("Deinonychus"): True
readOnlyDinosaurs[3]: Compsognathus
IndexOf("Compsognathus"): 3
Insert into the wrapped List:
Insert(2, "Oviraptor")
Tyrannosaurus
Amargasaurus
Oviraptor
Deinonychus
Compsognathus
Copied array has 7 elements:
""
"Tyrannosaurus"
"Amargasaurus"
"Oviraptor"
"Deinonychus"
"Compsognathus"
""
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.