List<T>.FindLast(Predicate<T>) List<T>.FindLast(Predicate<T>) List<T>.FindLast(Predicate<T>) List<T>.FindLast(Predicate<T>) Method

定義

指定された述語によって定義された条件と一致する要素を、List<T> 全体を対象に検索し、最もインデックス番号の大きい要素を返します。Searches for an element that matches the conditions defined by the specified predicate, and returns the last occurrence within the entire List<T>.

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

パラメーター

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

検索する要素の条件を定義する Predicate<T> デリゲート。The Predicate<T> delegate that defines the conditions of the element to search for.

戻り値

T T T T

見つかった場合は、指定された述語によって定義された条件と一致する最後の要素。それ以外の場合は、型 T の既定値。The last element that matches the conditions defined by the specified predicate, if found; otherwise, the default value for type T.

例外

次の例では、find メソッド、List<T>クラス。The following example demonstrates the find methods for the List<T> class. 例をList<T>クラスが含まれますbookクラスのオブジェクト、 Book、データを使用して、サンプル XML ファイル。書籍 (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). FillListメソッドの例では使用してLINQ to XMLのプロパティ値を XML から値を解析する、bookオブジェクト。The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

次の表では、find メソッドに提供される例について説明します。The following table describes the examples provided for the find methods.

メソッドMethod Example
Find(Predicate<T>) ID を使用して、本を検索、 IDToFind predicate デリゲートです。Finds a book by an ID using the IDToFind predicate delegate.

C# の例では、匿名デリゲートを使用します。C# example uses an anonymous delegate.
FindAll(Predicate<T>) すべての書籍を持つ検索Genreプロパティは、「コンピューター」を使用して、 FindComputer predicate デリゲートです。Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) 2001 年を使用する前に、発行日を含むコレクション内の最後の書籍を検索、 PubBefore2001 predicate デリゲートです。Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C# の例では、匿名デリゲートを使用します。C# example uses an anonymous delegate.
FindIndex(Predicate<T>) 最初のコンピューター書籍の使用のインデックスを検索、 FindComputer predicate デリゲートです。Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) 最後のコンピューター書籍の使用のインデックスを検索、 FindComputer predicate デリゲートです。Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) 最初のコンピューター書籍のインデックスを検索、コレクションの半分を使用して、 FindComputer predicate デリゲートです。Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) 最後のコンピューター書籍のインデックスを検索、コレクションの半分を使用して、 FindComputer predicate デリゲートです。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

注釈

Predicate<T>を返すメソッドにデリゲートtrueデリゲートで定義されている条件に一致するオブジェクトが渡された場合。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. 現在の要素List<T>に個別に渡される、Predicate<T>逆方向に移動、デリゲート、 List<T>、以降の最後の要素では、最初の要素で終わる。The elements of the current List<T> are individually passed to the Predicate<T> delegate, moving backward in the List<T>, starting with the last element and ending with the first element. 一致が見つかった場合は、処理が停止しました。Processing is stopped when a match is found.

重要

値の型を含む一覧を検索するときに、型の既定値は、検索述語を満たさないことを確認します。When searching a list containing value types, make sure the default value for the type does not satisfy the search predicate. それ以外の場合、一致が見つからなかったことを示す既定値と、型の既定値をリストの要素を区別する手段はありません。Otherwise, there is no way to distinguish between a default value indicating that no match was found and a list element that happens to have the default value for the type. 既定値は、検索述語を満たしている場合は、使用、FindLastIndexメソッド代わりにします。If the default value satisfies the search predicate, use the FindLastIndex method instead.

このメソッドは、一方向の検索を実行します。そのため、このメソッドは、O (n) 操作、 nCountします。This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

適用対象

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