List<T>.FindIndex 方法

定义

命名空间:: System.Collections.Generic

程序集:: mscorlib.dll, System.Collections.dll

程序集:: netstandard.dll, System.Collections.dll

程序集:: System.Collections.dll

程序集:: mscorlib.dll

程序集:: netstandard.dll

重要

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搜索与指定谓词定义的条件匹配的元素，并返回第一个匹配项或部分内 List<T> 第一个匹配项的从零开始的索引。如果未找到与条件匹配的项，此方法将返回 -1。

重载

名称	说明
FindIndex(Int32, Int32, Predicate<T>)	搜索与指定谓词定义的条件匹配的元素，并返回从指定索引开始且包含指定数量的元素 List<T> 范围内第一个匹配项的从零开始的索引。
FindIndex(Predicate<T>)	搜索与指定谓词定义的条件匹配的元素，并返回整个 List<T>中第一个匹配项的从零开始的索引。
FindIndex(Int32, Predicate<T>)	搜索与指定谓词定义的条件匹配的元素，并在从指定索引扩展到最后一个元素的元素 List<T> 范围内返回第一个匹配项的从零开始的索引。

FindIndex(Int32, Int32, Predicate<T>)

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

搜索与指定谓词定义的条件匹配的元素，并返回从指定索引开始且包含指定数量的元素 List<T> 范围内第一个匹配项的从零开始的索引。

public:
 int FindIndex(int startIndex, int count, Predicate<T> ^ match);

public int FindIndex(int startIndex, int count, Predicate<T> match);

member this.FindIndex : int * int * Predicate<'T> -> int

Public Function FindIndex (startIndex As Integer, count As Integer, match As Predicate(Of T)) As Integer

参数

startIndex: Int32

从零开始的搜索索引。

count: Int32

要搜索的节中的元素数。

match: Predicate<T>

定义 Predicate<T> 要搜索的元素条件的委托。

Int32

如果找到，则为第一个匹配条件的元素 match的第一个匹配项的从零开始的索引;否则为 -1。

例外

ArgumentNullException

match 是 null。

ArgumentOutOfRangeException

startIndex 超出有效索引 List<T>的范围。

-或-

count 小于 0。

-或-

startIndex 且 count 未在 .. 中 List<T>指定有效节。

示例

以下示例定义一个包含两个 Employee 字段的类， Name 以及 Id. 它还定义了一个 EmployeeSearch 具有单个方法的类， StartsWith该类指示字段是否 Employee.Name 以提供给 EmployeeSearch 类构造函数的指定子字符串开头。记下此方法的签名

public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

对应于可传递给方法的委托的 FindIndex 签名。该示例实例化一个 List<Employee> 对象，向该对象添加一些 Employee 对象，然后调用 FindIndex(Int32, Int32, Predicate<T>) 该方法两次以搜索整个集合（即索引 0 到索引 Count - 1 的成员）。第一次，它会搜索字段Employee以“J”开头的第一个Name对象;第二次搜索其Employee字段以“Ju”开头的第一个Name对象。

using System;
using System.Collections.Generic;

public class Employee : IComparable
{
   public String Name { get; set; }
   public int Id { get; set; }

   public int CompareTo(Object o )
   {
      Employee e = o as Employee;
      if (e == null)
         throw new ArgumentException("o is not an Employee object.");

      return Name.CompareTo(e.Name);
   }
}

public class EmployeeSearch
{
   String _s;

   public EmployeeSearch(String s)
   {
      _s = s;
   }

   public bool StartsWith(Employee e)
   {
      return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase);
   }
}

public class Example
{
   public static void Main()
   {
      var employees = new List<Employee>();
      employees.AddRange( new Employee[] { new Employee { Name = "Frank", Id = 2 },
                                           new Employee { Name = "Jill", Id = 3 },
                                           new Employee { Name = "Dave", Id = 5 },
                                           new Employee { Name = "Jack", Id = 8 },
                                           new Employee { Name = "Judith", Id = 12 },
                                           new Employee { Name = "Robert", Id = 14 },
                                           new Employee { Name = "Adam", Id = 1 } } );
      employees.Sort();

      var es = new EmployeeSearch("J");
      Console.WriteLine("'J' starts at index {0}",
                        employees.FindIndex(0, employees.Count - 1, es.StartsWith));

      es = new EmployeeSearch("Ju");
      Console.WriteLine("'Ju' starts at index {0}",
                        employees.FindIndex(0, employees.Count - 1,es.StartsWith));
   }
}
// The example displays the following output:
//       'J' starts at index 3
//       'Ju' starts at index 5

Imports System.Collections.Generic

Public Class Employee : Implements IComparable
   Public Property Name As String
   Public Property Id As Integer
   
   Public Function CompareTo(o As Object) As Integer _
         Implements IComparable.CompareTo
      Dim e As Employee = TryCast(o, Employee)
      If e Is Nothing Then
         Throw New ArgumentException("o is not an Employee object.")
      End If

      Return Name.CompareTo(e.Name)
   End Function
End Class

Public Class EmployeeSearch
   Dim _s As String
   
   Public Sub New(s As String)
      _s = s
   End Sub
   
   Public Function StartsWith(e As Employee) As Boolean
      Return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase)
   End Function
End Class

Module Example
   Public Sub Main()
      Dim employees As New List(Of Employee)()
      employees.AddRange( { New Employee() With { .Name = "Frank", .Id = 2 },
                            New Employee() With { .Name = "Jill", .Id = 3 },
                            New Employee() With { .Name = "Dave", .Id = 5 },
                            New Employee() With { .Name = "Jack", .Id = 8 },
                            New Employee() With { .Name = "Judith", .Id = 12 },
                            New Employee() With { .Name = "Robert", .Id = 14 },
                            New Employee() With { .Name = "Adam", .Id = 1 } } )
      employees.Sort()

      Dim es As New EmployeeSearch("J")
      Console.WriteLine("'J' starts at index {0}",
                        employees.FindIndex(0, employees.Count - 1,
                                            AddressOf es.StartsWith))
      es = New EmployeeSearch("Ju")
      Console.WriteLine("'Ju' starts at index {0}",
                        employees.FindIndex(0, employees.Count - 1,
                                            AddressOf es.StartsWith))
   End Sub
End Module
' The example displays the following output:
'       'J' starts at index 3
'       'Ju' starts at index 5

注解

List<T>如果大于 0，startIndex则从加startIndex减 1 开始count和结束count搜索前方。

Predicate<T>是方法的委托，如果传递给该方法的对象与委托中定义的条件匹配，则返回true该方法。当前 List<T> 元素单独传递给 Predicate<T> 委托。委托具有签名：

public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法执行线性搜索;因此，此方法是 O（n）操作，其中 n 为 count。

另请参阅

适用于

FindIndex(Predicate<T>)

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

搜索与指定谓词定义的条件匹配的元素，并返回整个 List<T>中第一个匹配项的从零开始的索引。

public:
 int FindIndex(Predicate<T> ^ match);

public int FindIndex(Predicate<T> match);

member this.FindIndex : Predicate<'T> -> int

Public Function FindIndex (match As Predicate(Of T)) As Integer

参数

match: Predicate<T>

定义 Predicate<T> 要搜索的元素条件的委托。

Int32

如果找到，则为第一个匹配条件的元素 match的第一个匹配项的从零开始的索引;否则为 -1。

例外

ArgumentNullException

match 是 null。

示例

public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

对应于可传递给方法的委托的 FindIndex 签名。该示例实例化一个List<Employee>对象，向该对象添加一些Employee对象，然后调用该方法两次以搜索整个集合，第一次调用FindIndex(Int32, Int32, Predicate<T>)其Employee字段以“J”开头的第Name一个对象，第二次调用其Employee字段以“Ju”开头的第一Name个对象。

using System;
using System.Collections.Generic;

public class Employee : IComparable
{
   public String Name { get; set; }
   public int Id { get; set; }

   public int CompareTo(Object o )
   {
      Employee e = o as Employee;
      if (e == null)
         throw new ArgumentException("o is not an Employee object.");

      return Name.CompareTo(e.Name);
   }
}

public class EmployeeSearch
{
   String _s;

   public EmployeeSearch(String s)
   {
      _s = s;
   }

   public bool StartsWith(Employee e)
   {
      return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase);
   }
}

public class Example
{
   public static void Main()
   {
      var employees = new List<Employee>();
      employees.AddRange( new Employee[] { new Employee { Name = "Frank", Id = 2 },
                                           new Employee { Name = "Jill", Id = 3 },
                                           new Employee { Name = "Dave", Id = 5 },
                                           new Employee { Name = "Jack", Id = 8 },
                                           new Employee { Name = "Judith", Id = 12 },
                                           new Employee { Name = "Robert", Id = 14 },
                                           new Employee { Name = "Adam", Id = 1 } } );
      employees.Sort();

      var es = new EmployeeSearch("J");
      Console.WriteLine("'J' starts at index {0}",
                        employees.FindIndex(es.StartsWith));

      es = new EmployeeSearch("Ju");
      Console.WriteLine("'Ju' starts at index {0}",
                        employees.FindIndex(es.StartsWith));
   }
}
// The example displays the following output:
//       'J' starts at index 3
//       'Ju' starts at index 5

Imports System.Collections.Generic

Public Class Employee : Implements IComparable
   Public Property Name As String
   Public Property Id As Integer
   
   Public Function CompareTo(o As Object) As Integer _
         Implements IComparable.CompareTo
      Dim e As Employee = TryCast(o, Employee)
      If e Is Nothing Then
         Throw New ArgumentException("o is not an Employee object.")
      End If

      Return Name.CompareTo(e.Name)
   End Function
End Class

Public Class EmployeeSearch
   Dim _s As String
   
   Public Sub New(s As String)
      _s = s
   End Sub
   
   Public Function StartsWith(e As Employee) As Boolean
      Return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase)
   End Function
End Class

Module Example
   Public Sub Main()
      Dim employees As New List(Of Employee)()
      employees.AddRange( { New Employee() With { .Name = "Frank", .Id = 2 },
                            New Employee() With { .Name = "Jill", .Id = 3 },
                            New Employee() With { .Name = "Dave", .Id = 5 },
                            New Employee() With { .Name = "Jack", .Id = 8 },
                            New Employee() With { .Name = "Judith", .Id = 12 },
                            New Employee() With { .Name = "Robert", .Id = 14 },
                            New Employee() With { .Name = "Adam", .Id = 1 } } )
      employees.Sort()

      Dim es As New EmployeeSearch("J")
      Console.WriteLine("'J' starts at index {0}",
                        employees.FindIndex(AddressOf es.StartsWith))
      es = New EmployeeSearch("Ju")
      Console.WriteLine("'Ju' starts at index {0}",
                        employees.FindIndex(AddressOf es.StartsWith))
   End Sub
End Module
' The example displays the following output:
'       'J' starts at index 3
'       'Ju' starts at index 5

注解

List<T>搜索从第一个元素开始，最后一个元素结束。

public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法执行线性搜索;因此，此方法是 O（n）操作，其中 n 为 Count。

另请参阅

适用于

FindIndex(Int32, Predicate<T>)

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

搜索与指定谓词定义的条件匹配的元素，并在从指定索引扩展到最后一个元素的元素 List<T> 范围内返回第一个匹配项的从零开始的索引。

public:
 int FindIndex(int startIndex, Predicate<T> ^ match);

public int FindIndex(int startIndex, Predicate<T> match);

member this.FindIndex : int * Predicate<'T> -> int

Public Function FindIndex (startIndex As Integer, match As Predicate(Of T)) As Integer

参数

startIndex: Int32

从零开始的搜索索引。

match: Predicate<T>

定义 Predicate<T> 要搜索的元素条件的委托。

Int32

如果找到，则为第一个匹配条件的元素 match的第一个匹配项的从零开始的索引;否则为 -1。

例外

ArgumentNullException

match 是 null。

ArgumentOutOfRangeException

startIndex 超出有效索引 List<T>的范围。

示例

public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

对应于可传递给方法的委托的 FindIndex 签名。该示例实例化一个 List<Employee> 对象，向其添加一些 Employee 对象，然后调用 FindIndex(Int32, Int32, Predicate<T>) 该方法两次，以搜索从第五个成员开始的集合（即索引 4 上的成员）。第一次，它会搜索字段Employee以“J”开头的第一个Name对象;第二次搜索其Employee字段以“Ju”开头的第一个Name对象。

using System;
using System.Collections.Generic;

public class Employee : IComparable
{
   public String Name { get; set; }
   public int Id { get; set; }

   public int CompareTo(Object o )
   {
      Employee e = o as Employee;
      if (e == null)
         throw new ArgumentException("o is not an Employee object.");

      return Name.CompareTo(e.Name);
   }
}

public class EmployeeSearch
{
   String _s;

   public EmployeeSearch(String s)
   {
      _s = s;
   }

   public bool StartsWith(Employee e)
   {
      return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase);
   }
}

public class Example
{
   public static void Main()
   {
      var employees = new List<Employee>();
      employees.AddRange( new Employee[] { new Employee { Name = "Frank", Id = 2 },
                                           new Employee { Name = "Jill", Id = 3 },
                                           new Employee { Name = "Dave", Id = 5 },
                                           new Employee { Name = "Jack", Id = 8 },
                                           new Employee { Name = "Judith", Id = 12 },
                                           new Employee { Name = "Robert", Id = 14 },
                                           new Employee { Name = "Adam", Id = 1 } } );
      employees.Sort();

      var es = new EmployeeSearch("J");
      int index = employees.FindIndex(4, es.StartsWith);
      Console.WriteLine("Starting index of'J': {0}",
                        index >= 0 ? index.ToString() : "Not found");

      es = new EmployeeSearch("Ju");
      index = employees.FindIndex(4, es.StartsWith);
      Console.WriteLine("Starting index of 'Ju': {0}",
                        index >= 0 ? index.ToString() : "Not found");
   }
}
// The example displays the following output:
//       'J' starts at index 4
//       'Ju' starts at index 5

Imports System.Collections.Generic

Public Class Employee : Implements IComparable
   Public Property Name As String
   Public Property Id As Integer
   
   Public Function CompareTo(o As Object) As Integer _
         Implements IComparable.CompareTo
      Dim e As Employee = TryCast(o, Employee)
      If e Is Nothing Then
         Throw New ArgumentException("o is not an Employee object.")
      End If

      Return Name.CompareTo(e.Name)
   End Function
End Class

Public Class EmployeeSearch
   Dim _s As String
   
   Public Sub New(s As String)
      _s = s
   End Sub
   
   Public Function StartsWith(e As Employee) As Boolean
      Return e.Name.StartsWith(_s, StringComparison.InvariantCultureIgnoreCase)
   End Function
End Class

Module Example
   Public Sub Main()
      Dim employees As New List(Of Employee)()
      employees.AddRange( { New Employee() With { .Name = "Frank", .Id = 2 },
                            New Employee() With { .Name = "Jill", .Id = 3 },
                            New Employee() With { .Name = "Dave", .Id = 5 },
                            New Employee() With { .Name = "Jack", .Id = 8 },
                            New Employee() With { .Name = "Judith", .Id = 12 },
                            New Employee() With { .Name = "Robert", .Id = 14 },
                            New Employee() With { .Name = "Adam", .Id = 1 } } )
      employees.Sort()

      Dim es As New EmployeeSearch("J")
      Dim index As Integer = employees.FindIndex(4, AddressOf es.StartsWith)        
      Console.WriteLine("Starting index of'J': {0}",
                        If(index >= 0, index.ToString(), "Not found"))

      es = New EmployeeSearch("Ju")
      index = employees.FindIndex(4, AddressOf es.StartsWith) 
      Console.WriteLine("Starting index of'Ju': {0}",
                        If(index >= 0, index.ToString(), "Not found"))

   End Sub
End Module
' The example displays the following output:
'       'J' starts at index 4
'       'Ju' starts at index 5

注解

List<T>从最后一个元素开始startIndex和结束，搜索前方。

public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法执行线性搜索;因此，此方法是一个 O（n）运算，其中 n 是元素数，从 startIndex 到末尾 List<T>。

另请参阅

适用于

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