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List<T>::FindIndex Method (Predicate<T>)

Updated: August 2009

Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the first occurrence within the entire List<T>.

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

public:
int FindIndex(
	Predicate<T>^ match
)

Parameters

match
Type: System::Predicate<T>

The Predicate<T> delegate that defines the conditions of the element to search for.

Return Value

Type: System::Int32
The zero-based index of the first occurrence of an element that matches the conditions defined by match, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

match is nullptr.

The List<T> is searched forward starting at the first element and ending at the last element.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of the current List<T> are individually passed to the Predicate<T> delegate.

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

The following example demonstrates the find methods for the List<T> class. The example for the List<T> class contains book objects, of class Book, using the data from the Sample XML File (books.xml). The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

The following table describes the examples provided for the find methods.

Method

Example

Find(Predicate<T>)

Finds a book by an ID using the IDToFind predicate delegate.

C# example uses an anonymous delegate.

FindAll(Predicate<T>)

Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.

FindLast(Predicate<T>)

Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C# example uses an anonymous delegate.

FindIndex(Predicate<T>)

Finds the index of first computer book using the FindComputer predicate delegate.

FindLastIndex(Predicate<T>)

Finds the index of the last computer book using the FindComputer predicate delegate.

FindIndex(Int32, Int32, Predicate<T>)

Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.

FindLastIndex(Int32, Int32, Predicate<T>)

Finds the index of last computer book in the second half of the collection, using the FindComputer predicate delegate.

No code example is currently available or this language may not be supported.

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

Date

History

Reason

August 2009

Improved example.

Information enhancement.

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