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List(T).FindIndex Method (Int32, Int32, Predicate(T))

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 range of elements in the List(T) that starts at the specified index and contains the specified number of elements.

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

member FindIndex : 
        startIndex:int * 
        count:int * 
        match:Predicate<'T> -> int 

Parameters

startIndex
Type: System.Int32
The zero-based starting index of the search.
count
Type: System.Int32
The number of elements in the section to search.
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 a null reference (Nothing in Visual Basic).

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for the List(T).

-or-

count is less than 0.

-or-

startIndex and count do not specify a valid section in the List(T).

The List(T) is searched forward starting at startIndex and ending at startIndex plus count minus 1, if count is greater than 0.

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 (LINQ to 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.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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