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Collection(T).IndexOf Method

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

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

abstract IndexOf : 
        item:'T -> int  
override IndexOf : 
        item:'T -> int

Parameters

item
Type: T

The object to locate in the List(T). The value can be a null reference (Nothing in Visual Basic) for reference types.

Return Value

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

Implements

IList(T).IndexOf(T)

The Collection(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(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(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.

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

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.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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