List<T>.FindLastIndex 方法

定义

搜索与指定谓词所定义的条件相匹配的元素,返回 List<T> 或它的一部分中最后一个匹配项的从零开始的索引。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.

重载

FindLastIndex(Predicate<T>)

搜索与指定谓词所定义的条件相匹配的元素,并返回整个 List<T> 中最后一个匹配元素的从零开始的索引。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>)

搜索与由指定谓词定义的条件相匹配的元素,并返回 List<T> 中从第一个元素到指定索引的元素范围内最后一个匹配项的从零开始的索引。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>)

搜索与指定谓词所定义的条件相匹配的元素,并返回 List<T> 中包含指定元素个数、到指定索引结束的元素范围内最后一个匹配项的从零开始的索引。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>)

搜索与指定谓词所定义的条件相匹配的元素,并返回整个 List<T> 中最后一个匹配元素的从零开始的索引。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

参数

match
Predicate<T>

Predicate<T> 委托,用于定义要搜索的元素的条件。The Predicate<T> delegate that defines the conditions of the element to search for.

返回

如果找到与 match 定义的条件相匹配的最后一个元素,则为该元素的从零开始的索引;否则为 -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

matchnullmatch is null.

示例

下面的示例演示了 List<T> 类的查找方法。The following example demonstrates the find methods for the List<T> class. List<T> 类的示例包含类 Bookbook 对象,使用示例 XML 文件中的数据:书籍(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). 示例中的 FillList 方法使用LINQ to XML将 XML 中的值分析为 book 对象的属性值。The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

下表介绍了为 find 方法提供的示例。The following table describes the examples provided for the find methods.

方法Method 示例Example
Find(Predicate<T>) 使用 IDToFind 谓词委托按 ID 查找书籍。Finds a book by an ID using the IDToFind predicate delegate.

C#示例使用匿名委托。C# example uses an anonymous delegate.
FindAll(Predicate<T>) 使用 FindComputer 谓词委托查找其 Genre 属性为 "Computer" 的所有书籍。Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) 使用 PubBefore2001 谓词委托,查找具有早于2001的发布日期的集合中的最后一本书。Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C#示例使用匿名委托。C# example uses an anonymous delegate.
FindIndex(Predicate<T>) 使用 FindComputer 谓词委托查找第一台计算机的索引。Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) 使用 FindComputer 谓词委托查找最后一台计算机的索引。Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) 使用 FindComputer 谓词委托,查找集合的后半部分中第一台计算机书籍的索引。Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) 使用 FindComputer 谓词委托,查找集合的后半部分中的最后一台计算机的索引。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

注解

从最后一个元素开始向后搜索 List<T>,并在第一个元素处结束。The List<T> is searched backward starting at the last element and ending at the first element.

Predicate<T> 是一个方法委托,如果传递给它的对象与委托中定义的条件相匹配,则该方法将返回 trueThe Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. 当前 List<T> 的元素分别传递到 Predicate<T> 委托。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

此方法执行线性搜索;因此,此方法的运算复杂度为 O (n),其中nCountThis method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

另请参阅

FindLastIndex(Int32, Predicate<T>)

搜索与由指定谓词定义的条件相匹配的元素,并返回 List<T> 中从第一个元素到指定索引的元素范围内最后一个匹配项的从零开始的索引。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

参数

startIndex
Int32

向后搜索的从零开始的起始索引。The zero-based starting index of the backward search.

match
Predicate<T>

Predicate<T> 委托,用于定义要搜索的元素的条件。The Predicate<T> delegate that defines the conditions of the element to search for.

返回

如果找到与 match 定义的条件相匹配的最后一个元素,则为该元素的从零开始的索引;否则为 -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

matchnullmatch is null.

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

注解

startIndex 开始向后搜索 List<T>,并在第一个元素处结束。The List<T> is searched backward starting at startIndex and ending at the first element.

Predicate<T> 是一个方法委托,如果传递给它的对象与委托中定义的条件相匹配,则该方法将返回 trueThe Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. 当前 List<T> 的元素分别传递到 Predicate<T> 委托。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

此方法执行线性搜索;因此,此方法的运算复杂度为 O (n),其中n是从 List<T> 开始到 startIndex的元素数。This 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.

另请参阅

FindLastIndex(Int32, Int32, Predicate<T>)

搜索与指定谓词所定义的条件相匹配的元素,并返回 List<T> 中包含指定元素个数、到指定索引结束的元素范围内最后一个匹配项的从零开始的索引。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

参数

startIndex
Int32

向后搜索的从零开始的起始索引。The zero-based starting index of the backward search.

count
Int32

要搜索的部分中的元素数。The number of elements in the section to search.

match
Predicate<T>

Predicate<T> 委托,用于定义要搜索的元素的条件。The Predicate<T> delegate that defines the conditions of the element to search for.

返回

如果找到与 match 定义的条件相匹配的最后一个元素,则为该元素的从零开始的索引;否则为 -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

matchnullmatch is null.

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

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

- 或 --or- startIndexcount 未在 List<T> 中指定有效部分。startIndex and count do not specify a valid section in the List<T>.

示例

下面的示例演示了 List<T> 类的查找方法。The following example demonstrates the find methods for the List<T> class. List<T> 类的示例包含类 Bookbook 对象,使用示例 XML 文件中的数据:书籍(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). 示例中的 FillList 方法使用LINQ to XML将 XML 中的值分析为 book 对象的属性值。The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.

下表介绍了为 find 方法提供的示例。The following table describes the examples provided for the find methods.

方法Method 示例Example
Find(Predicate<T>) 使用 IDToFind 谓词委托按 ID 查找书籍。Finds a book by an ID using the IDToFind predicate delegate.

C#示例使用匿名委托。C# example uses an anonymous delegate.
FindAll(Predicate<T>) 使用 FindComputer 谓词委托查找其 Genre 属性为 "Computer" 的所有书籍。Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate.
FindLast(Predicate<T>) 使用 PubBefore2001 谓词委托,查找具有早于2001的发布日期的集合中的最后一本书。Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate.

C#示例使用匿名委托。C# example uses an anonymous delegate.
FindIndex(Predicate<T>) 使用 FindComputer 谓词委托查找第一台计算机的索引。Finds the index of first computer book using the FindComputer predicate delegate.
FindLastIndex(Predicate<T>) 使用 FindComputer 谓词委托查找最后一台计算机的索引。Finds the index of the last computer book using the FindComputer predicate delegate.
FindIndex(Int32, Int32, Predicate<T>) 使用 FindComputer 谓词委托,查找集合的后半部分中第一台计算机书籍的索引。Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate.
FindLastIndex(Int32, Int32, Predicate<T>) 使用 FindComputer 谓词委托,查找集合的后半部分中的最后一台计算机的索引。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

注解

将从 startIndex 开始向后 List<T> 搜索,如果 count 大于0,则从 startIndex 减号开始,在 count 减号处结束。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> 是一个方法委托,如果传递给它的对象与委托中定义的条件相匹配,则该方法将返回 trueThe Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. 当前 List<T> 的元素分别传递到 Predicate<T> 委托。The elements of the current List<T> are individually passed to the Predicate<T> delegate.

此方法执行线性搜索;因此,此方法的运算复杂度为 O (n),其中ncountThis method performs a linear search; therefore, this method is an O(n) operation, where n is count.

另请参阅

适用于