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

定義

搜尋符合指定之述詞所定義的條件之元素,並傳回 List<T> 或其中一部分中最後一個項目之以零起始的索引。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.

多載

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

搜尋符合指定之述詞所定義的條件之元素,並傳回整個 List<T> 內最後一個相符項目之以零起始的索引。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>)

搜尋符合指定之述詞所定義的條件之項目,並傳回 List<T> 中從第一個項目延伸到指定之索引的項目範圍內,最後一個符合項目之以零為起始的索引。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>)

搜尋符合指定之述詞所定義的條件之元素,並傳回 List<T> 中包含指定之元素數目,且結束於指定之索引的元素範圍內最後一個符合項目之以零起始的索引。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>)

搜尋符合指定之述詞所定義的條件之元素,並傳回整個 List<T> 內最後一個相符項目之以零起始的索引。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

參數

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

定義要搜尋元素之條件的 Predicate<T> 委派。The Predicate<T> delegate that defines the conditions of the element to search for.

傳回

符合 match 所定義條件的元素,最後一次出現項目之以零為起始的索引 (若有找到),否則為 -1。The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

例外狀況

範例

下列範例示範的 find 方法List<T>類別。The following example demonstrates the find methods for the List<T> class. 範例List<T>類別包含book類別的物件Book,使用中的資料範例 XML 檔: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方法,在此範例會使用LINQ to XML來剖析的屬性值的值從 XMLbook物件。The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

下表說明提供給 find 方法範例。The following table describes the examples provided for the find methods.

方法Method 範例Example
Find(Predicate<T>) 找到識別碼使用的一本書IDToFind述詞委派。Finds a book by an ID using the IDToFind predicate delegate.

C# 範例會使用匿名委派。C# example uses an anonymous delegate.
FindAll(Predicate<T>) 尋找所有書籍,其Genre屬性是 「 電腦 」 使用FindComputer述詞委派。Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) 在 2001 年使用之前的發行日期的集合中找到的最後一本書PubBefore2001述詞委派。Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C# 範例會使用匿名委派。C# example uses an anonymous delegate.
FindIndex(Predicate<T>) 尋找索引的第一個電腦書籍使用FindComputer述詞委派。Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) 尋找索引的最後一個的電腦書籍使用FindComputer述詞委派。Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) 尋找索引的第一個電腦活頁簿中第二個一半的集合,使用FindComputer述詞委派。Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) 尋找索引的最後一個電腦活頁簿中第二個一半的集合,使用FindComputer述詞委派。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

備註

List<T>向後最後一個項目開始和結束時間的第一個項目搜尋。The List<T> is searched backward starting at the last element and ending at the first element.

Predicate<T>會傳回方法的委派true物件傳遞給是否符合委派中定義的條件。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. 目前的項目List<T>個別傳遞給Predicate<T>委派。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

這個方法會執行線性搜尋;因此,這個方法是 O (n) 運算,其中nCountThis method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

另請參閱

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

搜尋符合指定之述詞所定義的條件之項目,並傳回 List<T> 中從第一個項目延伸到指定之索引的項目範圍內,最後一個符合項目之以零為起始的索引。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

參數

startIndex
Int32 Int32 Int32 Int32

向後搜尋之以零為起始的起始索引。The zero-based starting index of the backward search.

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

定義要搜尋元素之條件的 Predicate<T> 委派。The Predicate<T> delegate that defines the conditions of the element to search for.

傳回

符合 match 所定義條件的元素,最後一次出現項目之以零為起始的索引 (若有找到),否則為 -1。The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

例外狀況

startIndex 超出 List<T> 的有效索引範圍。startIndex is outside the range of valid indexes for the List<T>.

備註

List<T>會搜尋回溯開始startIndex和結束時間的第一個元素。The List<T> is searched backward starting at startIndex and ending at the first element.

Predicate<T>會傳回方法的委派true物件傳遞給是否符合委派中定義的條件。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. 目前的項目List<T>個別傳遞給Predicate<T>委派。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

這個方法會執行線性搜尋;因此,這個方法是 O (n) 運算,其中n是從開頭的項目數List<T>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.

另請參閱

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

搜尋符合指定之述詞所定義的條件之元素,並傳回 List<T> 中包含指定之元素數目,且結束於指定之索引的元素範圍內最後一個符合項目之以零起始的索引。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

參數

startIndex
Int32 Int32 Int32 Int32

向後搜尋之以零為起始的起始索引。The zero-based starting index of the backward search.

count
Int32 Int32 Int32 Int32

區段中要搜尋的項目數目。The number of elements in the section to search.

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

定義要搜尋元素之條件的 Predicate<T> 委派。The Predicate<T> delegate that defines the conditions of the element to search for.

傳回

符合 match 所定義條件的元素,最後一次出現項目之以零為起始的索引 (若有找到),否則為 -1。The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

例外狀況

startIndex 超出 List<T> 的有效索引範圍。startIndex is outside the range of valid indexes for the List<T>.

-或--or- count 小於 0。count is less than 0.

-或--or- startIndexcount 不指定 List<T> 的有效區段。startIndex and count do not specify a valid section in the List<T>.

範例

下列範例示範的 find 方法List<T>類別。The following example demonstrates the find methods for the List<T> class. 範例List<T>類別包含book類別的物件Book,使用中的資料範例 XML 檔: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方法,在此範例會使用LINQ to XML來剖析的屬性值的值從 XMLbook物件。The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

下表說明提供給 find 方法範例。The following table describes the examples provided for the find methods.

方法Method 範例Example
Find(Predicate<T>) 找到識別碼使用的一本書IDToFind述詞委派。Finds a book by an ID using the IDToFind predicate delegate.

C# 範例會使用匿名委派。C# example uses an anonymous delegate.
FindAll(Predicate<T>) 尋找所有書籍,其Genre屬性是 「 電腦 」 使用FindComputer述詞委派。Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) 在 2001 年使用之前的發行日期的集合中找到的最後一本書PubBefore2001述詞委派。Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C# 範例會使用匿名委派。C# example uses an anonymous delegate.
FindIndex(Predicate<T>) 尋找索引的第一個電腦書籍使用FindComputer述詞委派。Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) 尋找索引的最後一個的電腦書籍使用FindComputer述詞委派。Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) 尋找索引的第一個電腦活頁簿中第二個一半的集合,使用FindComputer述詞委派。Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) 尋找索引的最後一個電腦活頁簿中第二個一半的集合,使用FindComputer述詞委派。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

備註

List<T>會搜尋回溯開始startIndex結尾startIndex減去count再加上 1,如果count大於 0。The List<T> is searched backward starting at startIndex and ending at startIndex minus count plus 1, if count is greater than 0.

Predicate<T>會傳回方法的委派true物件傳遞給是否符合委派中定義的條件。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. 目前的項目List<T>個別傳遞給Predicate<T>委派。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

這個方法會執行線性搜尋;因此,這個方法是 O (n) 運算,其中ncountThis method performs a linear search; therefore, this method is an O(n) operation, where n is count.

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