List<T>.FindLastIndex List<T>.FindLastIndex List<T>.FindLastIndex List<T>.FindLastIndex Method

Definición

Busca un elemento que cumpla las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en el objeto List<T> o en una parte del mismo.Searches for an element that matches the conditions defined by a specified predicate, and returns the zero-based index of the last occurrence within the List<T> or a portion of it.

Sobrecargas

FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en toda la matriz List<T>.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the entire List<T>.

FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en el intervalo de elementos de la matriz List<T> que va desde el primer elemento hasta el índice especificado.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the List<T> that extends from the first element to the specified index.

FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en el intervalo de elementos de la matriz List<T> que contiene el número especificado de elementos y termina en el índice especificado.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the List<T> that contains the specified number of elements and ends at the specified index.

FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>) FindLastIndex(Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en toda la matriz List<T>.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the entire List<T>.

public:
 int FindLastIndex(Predicate<T> ^ match);
public int FindLastIndex (Predicate<T> match);
member this.FindLastIndex : Predicate<'T> -> int
Public Function FindLastIndex (match As Predicate(Of T)) As Integer

Parámetros

match
Predicate<T> Predicate<T> Predicate<T> Predicate<T>

Delegado Predicate<T> que define las condiciones del elemento que se va a buscar.The Predicate<T> delegate that defines the conditions of the element to search for.

Devoluciones

Índice de base cero de la última aparición de un elemento que coincide con las condiciones definidas por match, si se encuentra; en caso contrario, -1.The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Excepciones

Ejemplos

En el ejemplo siguiente se muestran los métodos de List<T> búsqueda para la clase.The following example demonstrates the find methods for the List<T> class. El ejemplo de la List<T> clase contiene book objetos, de clase Book, con los datos del archivo XML de ejemplo: Libros (LINQ to XML).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). El FillList método en el ejemplo utiliza LINQ to XML para analizar los valores de XML en los valores de propiedad de book los objetos.The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

En la tabla siguiente se describen los ejemplos proporcionados para los métodos de búsqueda.The following table describes the examples provided for the find methods.

MétodoMethod EjemploExample
Find(Predicate<T>) Busca un libro mediante un identificador mediante el IDToFind delegado de predicado.Finds a book by an ID using the IDToFind predicate delegate.

C#en el ejemplo se usa un delegado anónimo.C# example uses an anonymous delegate.
FindAll(Predicate<T>) Busque todos los libros cuya Genre propiedad sea "Computer" mediante el FindComputer delegado de predicado.Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) Busca el último libro de la colección que tiene una fecha de publicación anterior a 2001, PubBefore2001 mediante el delegado de predicado.Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C#en el ejemplo se usa un delegado anónimo.C# example uses an anonymous delegate.
FindIndex(Predicate<T>) Busca el índice de la primera libreta de equipos FindComputer mediante el delegado de predicados.Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) Busca el índice del último libro de equipo mediante el FindComputer delegado de predicado.Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) Busca el índice del primer libro del equipo en la segunda mitad de la colección, utilizando FindComputer el delegado de predicado.Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) Busca el índice del último libro del equipo en la segunda mitad de la colección, utilizando FindComputer el delegado de predicado.Finds the index of last computer book in the second half of the collection, using the FindComputer predicate delegate.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace Find
{
    class Program
    {
        private static string IDtoFind = "bk109";

        private static List<Book> Books = new List<Book>();
        public static void Main(string[] args)
        {
            FillList();
            
            // Find a book by its ID.
            Book result = Books.Find(
            delegate(Book bk)
            {
                return bk.ID == IDtoFind;
            }
            );
            if (result != null)
            {
                DisplayResult(result, "Find by ID: " + IDtoFind);   
            }
            else
            {
                Console.WriteLine("\nNot found: {0}", IDtoFind);
            }


            // Find last book in collection published before 2001.
            result = Books.FindLast(
            delegate(Book bk)
            {
                DateTime year2001 = new DateTime(2001,01,01);
                return bk.Publish_date < year2001;
            });
            if (result != null)
            {
                DisplayResult(result, "Last book in collection published before 2001:");
            }
            else
            {
                Console.WriteLine("\nNot found: {0}", IDtoFind);
            }


            // Find all computer books.
            List<Book> results = Books.FindAll(FindComputer);
            if (results.Count != 0)
            {
                DisplayResults(results, "All computer:");
            }
            else
            {
                Console.WriteLine("\nNo books found.");
            }

            // Find all books under $10.00.
            results = Books.FindAll(
            delegate(Book bk)
            {
                return bk.Price < 10.00;
            }
            );
            if (results.Count != 0)
            {
                DisplayResults(results, "Books under $10:");
            }
            else
            {
                Console.WriteLine("\nNo books found.");
            }
            

            // Find index values.
            Console.WriteLine();
            int ndx = Books.FindIndex(FindComputer);
            Console.WriteLine("Index of first computer book: {0}", ndx);
            ndx = Books.FindLastIndex(FindComputer);
            Console.WriteLine("Index of last computer book: {0}", ndx);

            int mid = Books.Count / 2;
            ndx = Books.FindIndex(mid, mid, FindComputer);
            Console.WriteLine("Index of first computer book in the second half of the collection: {0}", ndx);
            
            ndx = Books.FindLastIndex(Books.Count - 1, mid, FindComputer);
            Console.WriteLine("Index of last computer book in the second half of the collection: {0}", ndx);

        }





        // Populates the list with sample data.
        private static void FillList()
        {
            
            // Create XML elements from a source file.
            XElement xTree = XElement.Load(@"c:\temp\books.xml");

            // Create an enumerable collection of the elements.
            IEnumerable<XElement> elements = xTree.Elements();

            // Evaluate each element and set set values in the book object.
            foreach (XElement el in elements)
            {
                Book book = new Book();
                book.ID = el.Attribute("id").Value;
                IEnumerable<XElement> props = el.Elements();
                foreach (XElement p in props)
                {


                    if (p.Name.ToString().ToLower() == "author")
                    {
                        book.Author = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "title")
                    {
                        book.Title = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "genre")
                    {
                        book.Genre = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "price")
                    {
                        book.Price = Convert.ToDouble(p.Value);
                    }
                    else if (p.Name.ToString().ToLower() == "publish_date")
                    {
                        book.Publish_date = Convert.ToDateTime(p.Value);
                    }
                    else if (p.Name.ToString().ToLower() == "description")
                    {
                        book.Description = p.Value;
                    }
                }

                Books.Add(book);

            }

            DisplayResults(Books, "All books:");

        }

        // Explicit predicate delegate.
        private static bool FindComputer(Book bk)
        {

            if (bk.Genre == "Computer")
            {
                return true;
            }
        else
            {
                return false;
            }

        }

        private static void DisplayResult(Book result, string title)
        {
            Console.WriteLine();
            Console.WriteLine(title);
            Console.WriteLine("\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", result.ID,
                result.Author, result.Title, result.Genre, result.Price,
                result.Publish_date.ToShortDateString());
            Console.WriteLine();


        }

        private static void DisplayResults(List<Book> results, string title)
        {
            Console.WriteLine();
            Console.WriteLine(title);
            foreach (Book b in results)
            {

                Console.Write("\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", b.ID,
                    b.Author, b.Title, b.Genre, b.Price,
                    b.Publish_date.ToShortDateString());
            }
            Console.WriteLine();

        }

    }

    public class Book
    {
        public string ID { get; set; }
        public string Author { get; set; }
        public string Title { get; set; }
        public string Genre { get; set; }
        public double Price { get; set; }
        public DateTime Publish_date { get; set; }
        public string Description { get; set; }
    }
}
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1

    Private IDToFind As String = "bk109"

    Public Books As New List(Of Book)


    Sub Main()

        FillList()

        ' Find a book by its ID.
        Dim result As Book = Books.Find(AddressOf FindID)
        If result IsNot Nothing Then
            DisplayResult(result, "Find by ID: " & IDToFind)
        Else

            Console.WriteLine(vbCrLf & "Not found: " & IDToFind)
        End If
        Console.WriteLine()

        ' Find last book in collection that has a publish date before 2001.
        result = Books.FindLast(AddressOf PubBefore2001)
        If result IsNot Nothing Then
            DisplayResult(result, "Last book in collection published before 2001:")
        Else
            Console.WriteLine(vbCrLf & "Not found: " & IDToFind)
        End If
        Console.WriteLine()

        ' Find all computer books.
        Dim results As List(Of Book) = Books.FindAll(AddressOf FindComputer)
        If results.Count <> 0 Then
            DisplayResults(results, "All computer books:")
        Else
            Console.WriteLine(vbCrLf & "No books found.")
        End If
        Console.WriteLine()


        ' Find all books under $10.00.
        results = Books.FindAll(AddressOf FindUnderTen)
        If results.Count <> 0 Then
            DisplayResults(results, "Books under $10:")
        Else
            Console.WriteLine(vbCrLf & "No books found.")
        End If
        Console.WriteLine()

        ' Find index values.
        Console.WriteLine()
        Dim ndx As Integer = Books.FindIndex(AddressOf FindComputer)
        Console.WriteLine("Index of first computer book: " & ndx)
        ndx = Books.FindLastIndex(AddressOf FindComputer)
        Console.WriteLine("Index of last computer book: " & ndx)

        Dim mid As Integer = Books.Count / 2
        ndx = Books.FindIndex(mid, mid, AddressOf FindComputer)
        Console.WriteLine("Index of first computer book in the second half of the collection: " & ndx)



        ndx = Books.FindLastIndex(Books.Count - 1, mid, AddressOf FindComputer)
        Console.WriteLine("Index of last computer book in the second half of the collection: " & ndx)


    End Sub



    Private Sub FillList()

        ' Create XML elements from a source file.
        Dim xTree As XElement = XElement.Load("c:\temp\books.xml")

        ' Create an enumerable collection of the elements.
        Dim elements As IEnumerable(Of XElement) = xTree.Elements

        ' Evaluate each element and set values in the book object.
        For Each el As XElement In elements
            Dim Book As New Book()
            Book.ID = el.Attribute("id").Value
            Dim props As IEnumerable(Of XElement) = el.Elements
            For Each p As XElement In props
                If p.Name.ToString.ToLower = "author" Then
                    Book.Author = p.Value
                End If
                If p.Name.ToString.ToLower = "title" Then
                    Book.Title = p.Value
                End If
                If p.Name.ToString.ToLower = "genre" Then
                    Book.Genre = p.Value
                End If
                If p.Name.ToString.ToLower = "price" Then
                    Book.Price = Convert.ToDouble(p.Value)
                End If
                If p.Name.ToString.ToLower = "publish_date" Then
                    Book.Publish_date = Convert.ToDateTime(p.Value)
                End If
                If p.Name.ToString.ToLower = "description" Then
                    Book.Description = p.Value
                End If
            Next
            Books.Add(Book)
        Next

        DisplayResults(Books, "All books:")
        Console.WriteLine()

    End Sub

    ' Predicate delegates for
    ' Find and FindAll methods.
    Private Function FindID(ByVal bk As Book) As Boolean
        If bk.ID = IDToFind Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function FindComputer(ByVal bk As Book) As Boolean
        If bk.Genre = "Computer" Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function FindUnderTen(ByVal bk As Book) As Boolean
        Dim tendollars As Double = 10.0
        If bk.Price < tendollars Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function PubBefore2001(ByVal bk As Book) As Boolean
        Dim year2001 As DateTime = New DateTime(2001, 1, 1)
        Return bk.Publish_date < year2001
    End Function
    Private Sub DisplayResult(ByVal result As Book, ByVal title As String)
        Console.WriteLine()
        Console.WriteLine(title)
        Console.WriteLine(vbLf & result.ID & vbTab & result.Author & _
                          vbTab & result.Title & vbTab & result.Genre & _
                          vbTab & result.Publish_date & vbTab & result.Price)
        Console.WriteLine()
    End Sub
    Private Sub DisplayResults(ByVal results As List(Of Book), ByVal title As String)
        Console.WriteLine()
        Console.WriteLine(title)
        For Each b As Book In results
            Console.Write(vbLf & b.ID & vbTab & b.Author & _
                              vbTab & b.Title & vbTab & b.Genre & _
                              vbTab & b.Publish_date & vbTab & b.Price)
        Next
        Console.WriteLine()
    End Sub

    Public Class Book
        Public ID As String
        Public Author As String
        Public Title As String
        Public Genre As String
        Public Price As Double
        Public Publish_date As DateTime
        Public Description As String
    End Class


End Module

Comentarios

List<T> Se busca hacia atrás a partir del último elemento y finalizando en el primer elemento.The List<T> is searched backward starting at the last element and ending at the first element.

Es un delegado de un método que devuelve true si el objeto que se pasa coincide con las condiciones definidas en el delegado. Predicate<T>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. Los elementos del actual List<T> se pasan individualmente Predicate<T> al delegado.The elements of the current List<T> are individually passed to the Predicate<T> delegate.

Este método realiza una búsqueda lineal; por lo tanto, este método es una operación O (n), donde Count n es.This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

Consulte también:

FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>) FindLastIndex(Int32, Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en el intervalo de elementos de la matriz List<T> que va desde el primer elemento hasta el índice especificado.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the List<T> that extends from the first element to the specified index.

public:
 int FindLastIndex(int startIndex, Predicate<T> ^ match);
public int FindLastIndex (int startIndex, Predicate<T> match);
member this.FindLastIndex : int * Predicate<'T> -> int
Public Function FindLastIndex (startIndex As Integer, match As Predicate(Of T)) As Integer

Parámetros

startIndex
Int32 Int32 Int32 Int32

Índice inicial de base cero de la búsqueda hacia atrás.The zero-based starting index of the backward search.

match
Predicate<T> Predicate<T> Predicate<T> Predicate<T>

Delegado Predicate<T> que define las condiciones del elemento que se va a buscar.The Predicate<T> delegate that defines the conditions of the element to search for.

Devoluciones

Índice de base cero de la última aparición de un elemento que coincide con las condiciones definidas por match, si se encuentra; en caso contrario, -1.The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Excepciones

startIndex está fuera del intervalo de índices válidos para List<T>.startIndex is outside the range of valid indexes for the List<T>.

Comentarios

Se busca hacia atrás a partir de startIndex y finaliza en el primer elemento. List<T>The List<T> is searched backward starting at startIndex and ending at the first element.

Es un delegado de un método que devuelve true si el objeto que se pasa coincide con las condiciones definidas en el delegado. Predicate<T>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. Los elementos del actual List<T> se pasan individualmente Predicate<T> al delegado.The elements of the current List<T> are individually passed to the Predicate<T> delegate.

Este método realiza una búsqueda lineal; por consiguiente, este método es una operación O (n), donde n es el número de elementos desde el List<T> principio de hasta. startIndexThis method performs a linear search; therefore, this method is an O(n) operation, where n is the number of elements from the beginning of the List<T> to startIndex.

Consulte también:

FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>) FindLastIndex(Int32, Int32, Predicate<T>)

Busca un elemento que coincida con las condiciones definidas por el predicado especificado y devuelve el índice de base cero de la última aparición en el intervalo de elementos de la matriz List<T> que contiene el número especificado de elementos y termina en el índice especificado.Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the List<T> that contains the specified number of elements and ends at the specified index.

public:
 int FindLastIndex(int startIndex, int count, Predicate<T> ^ match);
public int FindLastIndex (int startIndex, int count, Predicate<T> match);
member this.FindLastIndex : int * int * Predicate<'T> -> int
Public Function FindLastIndex (startIndex As Integer, count As Integer, match As Predicate(Of T)) As Integer

Parámetros

startIndex
Int32 Int32 Int32 Int32

Índice inicial de base cero de la búsqueda hacia atrás.The zero-based starting index of the backward search.

count
Int32 Int32 Int32 Int32

Número de elementos de la sección en la que se va a realizar la búsqueda.The number of elements in the section to search.

match
Predicate<T> Predicate<T> Predicate<T> Predicate<T>

Delegado Predicate<T> que define las condiciones del elemento que se va a buscar.The Predicate<T> delegate that defines the conditions of the element to search for.

Devoluciones

Índice de base cero de la última aparición de un elemento que coincide con las condiciones definidas por match, si se encuentra; en caso contrario, -1.The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Excepciones

startIndex está fuera del intervalo de índices válidos para List<T>.startIndex is outside the range of valid indexes for the List<T>.

O bien-or- count es menor que 0.count is less than 0.

O bien-or- startIndex y count no especifican una sección válida en List<T>.startIndex and count do not specify a valid section in the List<T>.

Ejemplos

En el ejemplo siguiente se muestran los métodos de List<T> búsqueda para la clase.The following example demonstrates the find methods for the List<T> class. El ejemplo de la List<T> clase contiene book objetos, de clase Book, con los datos del archivo XML de ejemplo: Libros (LINQ to XML).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). El FillList método en el ejemplo utiliza LINQ to XML para analizar los valores de XML en los valores de propiedad de book los objetos.The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

En la tabla siguiente se describen los ejemplos proporcionados para los métodos de búsqueda.The following table describes the examples provided for the find methods.

MétodoMethod EjemploExample
Find(Predicate<T>) Busca un libro mediante un identificador mediante el IDToFind delegado de predicado.Finds a book by an ID using the IDToFind predicate delegate.

C#en el ejemplo se usa un delegado anónimo.C# example uses an anonymous delegate.
FindAll(Predicate<T>) Busque todos los libros cuya Genre propiedad sea "Computer" mediante el FindComputer delegado de predicado.Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) Busca el último libro de la colección que tiene una fecha de publicación anterior a 2001, PubBefore2001 mediante el delegado de predicado.Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C#en el ejemplo se usa un delegado anónimo.C# example uses an anonymous delegate.
FindIndex(Predicate<T>) Busca el índice de la primera libreta de equipos FindComputer mediante el delegado de predicados.Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) Busca el índice del último libro de equipo mediante el FindComputer delegado de predicado.Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) Busca el índice del primer libro del equipo en la segunda mitad de la colección, utilizando FindComputer el delegado de predicado.Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) Busca el índice del último libro del equipo en la segunda mitad de la colección, utilizando FindComputer el delegado de predicado.Finds the index of last computer book in the second half of the collection, using the FindComputer predicate delegate.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace Find
{
    class Program
    {
        private static string IDtoFind = "bk109";

        private static List<Book> Books = new List<Book>();
        public static void Main(string[] args)
        {
            FillList();
            
            // Find a book by its ID.
            Book result = Books.Find(
            delegate(Book bk)
            {
                return bk.ID == IDtoFind;
            }
            );
            if (result != null)
            {
                DisplayResult(result, "Find by ID: " + IDtoFind);   
            }
            else
            {
                Console.WriteLine("\nNot found: {0}", IDtoFind);
            }


            // Find last book in collection published before 2001.
            result = Books.FindLast(
            delegate(Book bk)
            {
                DateTime year2001 = new DateTime(2001,01,01);
                return bk.Publish_date < year2001;
            });
            if (result != null)
            {
                DisplayResult(result, "Last book in collection published before 2001:");
            }
            else
            {
                Console.WriteLine("\nNot found: {0}", IDtoFind);
            }


            // Find all computer books.
            List<Book> results = Books.FindAll(FindComputer);
            if (results.Count != 0)
            {
                DisplayResults(results, "All computer:");
            }
            else
            {
                Console.WriteLine("\nNo books found.");
            }

            // Find all books under $10.00.
            results = Books.FindAll(
            delegate(Book bk)
            {
                return bk.Price < 10.00;
            }
            );
            if (results.Count != 0)
            {
                DisplayResults(results, "Books under $10:");
            }
            else
            {
                Console.WriteLine("\nNo books found.");
            }
            

            // Find index values.
            Console.WriteLine();
            int ndx = Books.FindIndex(FindComputer);
            Console.WriteLine("Index of first computer book: {0}", ndx);
            ndx = Books.FindLastIndex(FindComputer);
            Console.WriteLine("Index of last computer book: {0}", ndx);

            int mid = Books.Count / 2;
            ndx = Books.FindIndex(mid, mid, FindComputer);
            Console.WriteLine("Index of first computer book in the second half of the collection: {0}", ndx);
            
            ndx = Books.FindLastIndex(Books.Count - 1, mid, FindComputer);
            Console.WriteLine("Index of last computer book in the second half of the collection: {0}", ndx);

        }





        // Populates the list with sample data.
        private static void FillList()
        {
            
            // Create XML elements from a source file.
            XElement xTree = XElement.Load(@"c:\temp\books.xml");

            // Create an enumerable collection of the elements.
            IEnumerable<XElement> elements = xTree.Elements();

            // Evaluate each element and set set values in the book object.
            foreach (XElement el in elements)
            {
                Book book = new Book();
                book.ID = el.Attribute("id").Value;
                IEnumerable<XElement> props = el.Elements();
                foreach (XElement p in props)
                {


                    if (p.Name.ToString().ToLower() == "author")
                    {
                        book.Author = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "title")
                    {
                        book.Title = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "genre")
                    {
                        book.Genre = p.Value;
                    }
                    else if (p.Name.ToString().ToLower() == "price")
                    {
                        book.Price = Convert.ToDouble(p.Value);
                    }
                    else if (p.Name.ToString().ToLower() == "publish_date")
                    {
                        book.Publish_date = Convert.ToDateTime(p.Value);
                    }
                    else if (p.Name.ToString().ToLower() == "description")
                    {
                        book.Description = p.Value;
                    }
                }

                Books.Add(book);

            }

            DisplayResults(Books, "All books:");

        }

        // Explicit predicate delegate.
        private static bool FindComputer(Book bk)
        {

            if (bk.Genre == "Computer")
            {
                return true;
            }
        else
            {
                return false;
            }

        }

        private static void DisplayResult(Book result, string title)
        {
            Console.WriteLine();
            Console.WriteLine(title);
            Console.WriteLine("\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", result.ID,
                result.Author, result.Title, result.Genre, result.Price,
                result.Publish_date.ToShortDateString());
            Console.WriteLine();


        }

        private static void DisplayResults(List<Book> results, string title)
        {
            Console.WriteLine();
            Console.WriteLine(title);
            foreach (Book b in results)
            {

                Console.Write("\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", b.ID,
                    b.Author, b.Title, b.Genre, b.Price,
                    b.Publish_date.ToShortDateString());
            }
            Console.WriteLine();

        }

    }

    public class Book
    {
        public string ID { get; set; }
        public string Author { get; set; }
        public string Title { get; set; }
        public string Genre { get; set; }
        public double Price { get; set; }
        public DateTime Publish_date { get; set; }
        public string Description { get; set; }
    }
}
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1

    Private IDToFind As String = "bk109"

    Public Books As New List(Of Book)


    Sub Main()

        FillList()

        ' Find a book by its ID.
        Dim result As Book = Books.Find(AddressOf FindID)
        If result IsNot Nothing Then
            DisplayResult(result, "Find by ID: " & IDToFind)
        Else

            Console.WriteLine(vbCrLf & "Not found: " & IDToFind)
        End If
        Console.WriteLine()

        ' Find last book in collection that has a publish date before 2001.
        result = Books.FindLast(AddressOf PubBefore2001)
        If result IsNot Nothing Then
            DisplayResult(result, "Last book in collection published before 2001:")
        Else
            Console.WriteLine(vbCrLf & "Not found: " & IDToFind)
        End If
        Console.WriteLine()

        ' Find all computer books.
        Dim results As List(Of Book) = Books.FindAll(AddressOf FindComputer)
        If results.Count <> 0 Then
            DisplayResults(results, "All computer books:")
        Else
            Console.WriteLine(vbCrLf & "No books found.")
        End If
        Console.WriteLine()


        ' Find all books under $10.00.
        results = Books.FindAll(AddressOf FindUnderTen)
        If results.Count <> 0 Then
            DisplayResults(results, "Books under $10:")
        Else
            Console.WriteLine(vbCrLf & "No books found.")
        End If
        Console.WriteLine()

        ' Find index values.
        Console.WriteLine()
        Dim ndx As Integer = Books.FindIndex(AddressOf FindComputer)
        Console.WriteLine("Index of first computer book: " & ndx)
        ndx = Books.FindLastIndex(AddressOf FindComputer)
        Console.WriteLine("Index of last computer book: " & ndx)

        Dim mid As Integer = Books.Count / 2
        ndx = Books.FindIndex(mid, mid, AddressOf FindComputer)
        Console.WriteLine("Index of first computer book in the second half of the collection: " & ndx)



        ndx = Books.FindLastIndex(Books.Count - 1, mid, AddressOf FindComputer)
        Console.WriteLine("Index of last computer book in the second half of the collection: " & ndx)


    End Sub



    Private Sub FillList()

        ' Create XML elements from a source file.
        Dim xTree As XElement = XElement.Load("c:\temp\books.xml")

        ' Create an enumerable collection of the elements.
        Dim elements As IEnumerable(Of XElement) = xTree.Elements

        ' Evaluate each element and set values in the book object.
        For Each el As XElement In elements
            Dim Book As New Book()
            Book.ID = el.Attribute("id").Value
            Dim props As IEnumerable(Of XElement) = el.Elements
            For Each p As XElement In props
                If p.Name.ToString.ToLower = "author" Then
                    Book.Author = p.Value
                End If
                If p.Name.ToString.ToLower = "title" Then
                    Book.Title = p.Value
                End If
                If p.Name.ToString.ToLower = "genre" Then
                    Book.Genre = p.Value
                End If
                If p.Name.ToString.ToLower = "price" Then
                    Book.Price = Convert.ToDouble(p.Value)
                End If
                If p.Name.ToString.ToLower = "publish_date" Then
                    Book.Publish_date = Convert.ToDateTime(p.Value)
                End If
                If p.Name.ToString.ToLower = "description" Then
                    Book.Description = p.Value
                End If
            Next
            Books.Add(Book)
        Next

        DisplayResults(Books, "All books:")
        Console.WriteLine()

    End Sub

    ' Predicate delegates for
    ' Find and FindAll methods.
    Private Function FindID(ByVal bk As Book) As Boolean
        If bk.ID = IDToFind Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function FindComputer(ByVal bk As Book) As Boolean
        If bk.Genre = "Computer" Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function FindUnderTen(ByVal bk As Book) As Boolean
        Dim tendollars As Double = 10.0
        If bk.Price < tendollars Then
            Return True
        Else
            Return False
        End If
    End Function
    Private Function PubBefore2001(ByVal bk As Book) As Boolean
        Dim year2001 As DateTime = New DateTime(2001, 1, 1)
        Return bk.Publish_date < year2001
    End Function
    Private Sub DisplayResult(ByVal result As Book, ByVal title As String)
        Console.WriteLine()
        Console.WriteLine(title)
        Console.WriteLine(vbLf & result.ID & vbTab & result.Author & _
                          vbTab & result.Title & vbTab & result.Genre & _
                          vbTab & result.Publish_date & vbTab & result.Price)
        Console.WriteLine()
    End Sub
    Private Sub DisplayResults(ByVal results As List(Of Book), ByVal title As String)
        Console.WriteLine()
        Console.WriteLine(title)
        For Each b As Book In results
            Console.Write(vbLf & b.ID & vbTab & b.Author & _
                              vbTab & b.Title & vbTab & b.Genre & _
                              vbTab & b.Publish_date & vbTab & b.Price)
        Next
        Console.WriteLine()
    End Sub

    Public Class Book
        Public ID As String
        Public Author As String
        Public Title As String
        Public Genre As String
        Public Price As Double
        Public Publish_date As DateTime
        Public Description As String
    End Class


End Module

Comentarios

startIndex startIndex count count Se busca hacia atrás a partir de y termina con menos más 1, si es mayor que 0. List<T>The List<T> is searched backward starting at startIndex and ending at startIndex minus count plus 1, if count is greater than 0.

Es un delegado de un método que devuelve true si el objeto que se pasa coincide con las condiciones definidas en el delegado. Predicate<T>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. Los elementos del actual List<T> se pasan individualmente Predicate<T> al delegado.The elements of the current List<T> are individually passed to the Predicate<T> delegate.

Este método realiza una búsqueda lineal; por lo tanto, este método es una operación O (n), donde count n es.This method performs a linear search; therefore, this method is an O(n) operation, where n is count.

Consulte también:

Se aplica a