List(Of T).IndexOf Method (T)

 

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

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

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 null for reference types.

Return Value

Type: System.Int32

The zero-based index of the first occurrence of item within the entire List(Of T), if found; otherwise, –1.

The List(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, this method is an O(n) operation, where n is Count.

The following example demonstrates all three overloads of the IndexOf method. A List(Of T) of strings is created, with one entry that appears twice, at index location 0 and index location 5. The IndexOf(T) method overload searches the list from the beginning, and finds the first occurrence of the string. The IndexOf(T, Int32) method overload is used to search the list beginning with index location 3 and continuing to the end of the list, and finds the second occurrence of the string. Finally, the IndexOf(T, Int32, Int32) method overload is used to search a range of two entries, beginning at index location two; it returns –1 because there are no instances of the search string in that range.

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Brachiosaurus")
        dinosaurs.Add("Deinonychus")
        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Compsognathus")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

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

        Console.WriteLine(vbLf & _
            "IndexOf(""Tyrannosaurus"", 3): {0}", _
            dinosaurs.IndexOf("Tyrannosaurus", 3))

        Console.WriteLine(vbLf & _
            "IndexOf(""Tyrannosaurus"", 2, 2): {0}", _
            dinosaurs.IndexOf("Tyrannosaurus", 2, 2))

    End Sub
End Class

' This code example produces the following output:
'
'Tyrannosaurus
'Amargasaurus
'Mamenchisaurus
'Brachiosaurus
'Deinonychus
'Tyrannosaurus
'Compsognathus
'
'IndexOf("Tyrannosaurus"): 0
'
'IndexOf("Tyrannosaurus", 3): 5
'
'IndexOf("Tyrannosaurus", 2, 2): -1

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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