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Collection(Of T).IndexOf Method

Searches for the specified object and returns the zero-based index of the first occurrence within the entire Collection(Of T).

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

'Declaration
Public Function IndexOf ( _
	item As T _
) As Integer

Parameters

item
Type: T
The object to locate in the List(Of T). The value can be Nothing for reference types.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of item within the entire Collection(Of T), if found; otherwise, -1.

Implements

IList(Of T).IndexOf(T)

The Collection(Of T) is searched forward starting at the first element and ending at the last element.

This method determines equality using the default equality comparer EqualityComparer(Of T).Default for T, the type of values in the list.

This method performs a linear search; therefore, the average execution time is proportional to Count. That is, this method is an O(n) operation, where n is Count.

The following code example demonstrates many of the properties and methods of Collection(Of T). The code example creates a collection of strings, uses the Add method to add several strings, displays the Count, and lists the strings. The example uses the IndexOf method to find the index of a string and the Contains method to determine whether a string is in the collection. The example inserts a string using the Insert method and retrieves and sets strings using the default Item property (the indexer in C#). The example removes strings by string identity using the Remove method and by index using the RemoveAt method. Finally, the Clear method is used to clear all strings from the collection.


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 Collection(Of String)

        dinosaurs.Add("Psitticosaurus")
        dinosaurs.Add("Caudipteryx")
        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Muttaburrasaurus")

        outputBlock.Text += String.Format("{0} dinosaurs:", dinosaurs.Count) & vbCrLf
        Display(outputBlock, dinosaurs)

        outputBlock.Text &= vbLf & String.Format("IndexOf(""Muttaburrasaurus"") {0}", _
          dinosaurs.IndexOf("Muttaburrasaurus")) & vbCrLf

        outputBlock.Text &= vbLf & String.Format("Contains(""Caudipteryx"") {0}", _
          dinosaurs.Contains("Caudipteryx")) & vbCrLf

        outputBlock.Text += String.Format(vbLf & "Insert(2, ""Nanotyrannus"")") & vbCrLf
        dinosaurs.Insert(2, "Nanotyrannus")
        Display(outputBlock, dinosaurs)

        outputBlock.Text += String.Format(vbLf & "dinosaurs(2): {0}", dinosaurs(2)) & vbCrLf

        outputBlock.Text &= vbLf & "dinosaurs(2) = ""Microraptor""" & vbCrLf
        dinosaurs(2) = "Microraptor"
        Display(outputBlock, dinosaurs)

        outputBlock.Text &= vbLf & "Remove(""Microraptor"")" & vbCrLf
        dinosaurs.Remove("Microraptor")
        Display(outputBlock, dinosaurs)

        outputBlock.Text &= vbLf & "RemoveAt(0)" & vbCrLf
        dinosaurs.RemoveAt(0)
        Display(outputBlock, dinosaurs)

        outputBlock.Text &= vbLf & "dinosaurs.Clear()" & vbCrLf
        dinosaurs.Clear()
        outputBlock.Text += String.Format("Count: {0}", dinosaurs.Count) & vbCrLf

    End Sub

    Private Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal cs As Collection(Of String))
        outputBlock.Text &= vbCrLf
        For Each item As String In cs
            outputBlock.Text &= item & vbCrLf
        Next item
    End Sub
End Class

' This code example produces the following output:
'
'4 dinosaurs:
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'IndexOf("Muttaburrasaurus"): 3
'
'Contains("Caudipteryx"): True
'
'Insert(2, "Nanotyrannus")
'
'Psitticosaurus
'Caudipteryx
'Nanotyrannus
'Compsognathus
'Muttaburrasaurus
'
'dinosaurs(2): Nanotyrannus
'
'dinosaurs(2) = "Microraptor"
'
'Psitticosaurus
'Caudipteryx
'Microraptor
'Compsognathus
'Muttaburrasaurus
'
'Remove("Microraptor")
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'RemoveAt(0)
'
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'dinosaurs.Clear()
'Count: 0


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

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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