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Code  ›  List<t>.FindIndex 方法 (System.Collections.Generic) | Microsoft Learn</t>
https://learn.microsoft.com/zh-tw/dotnet/api/system.collections.generic.list-1.findindex?view=net-8.0
笑点低的荒野
4 月前 
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

下列範例會定義具有兩個 Employee 欄位 Name 和 Id 的類別。 它也會使用單一 EmployeeSearch 方法定義類別， StartsWith 指出欄位是否 Employee.Name 以提供給類別建構函式的 EmployeeSearch 指定子字串開頭。 請注意此方法的簽章 

public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

會對應至可以傳遞至 方法之委派的 FindIndex 簽章。 此範例會具現化 List<Employee> 物件、將一些 Employee 物件加入其中，然後呼叫 FindIndex(Int32, Int32, Predicate<T>) 方法兩次來搜尋整個集合 (，也就是索引 0 到 index Count 的成員 - 1) 。 第一次，它會搜尋欄位開頭為 “J” 的第一個 Employee 物件 Name ;第二次，它會搜尋字段開頭為 “Ju” 的第一個 Employee 物件 Name 。


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
    	
List<T>如果 大於 0，count則會從 開始startIndex搜尋 ，並結束於 startIndex 加count號減 1。


Predicate<T>是方法的委派，如果傳遞至該方法的物件符合委派中定義的條件，則會傳回 true 。  目前 List<T> 的專案會個別傳遞至 Predicate<T> 委派。 委派具有簽章：


public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法會執行線性搜尋;因此，這個方法是 o (n) 作業，其中 n 是 count。

 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

    	
下列範例會定義具有兩個 Employee 欄位 Name 和 Id的類別。 它也會使用單一 EmployeeSearch 方法定義類別， StartsWith指出欄位是否 Employee.Name 以提供給類別建構函式的 EmployeeSearch 指定子字串開頭。 請注意此方法的簽章


public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

會對應至可以傳遞至 方法之委派的 FindIndex 簽章。 此範例會具現化 List<Employee> 物件、將一些Employee物件加入其中，然後呼叫 FindIndex(Int32, Int32, Predicate<T>) 方法兩次來搜尋整個集合，第一次針對字段開頭為 “J” 的第一個Employee物件，第二次呼叫字段開頭為 “Ju” 的第一個Employee物件NameName。


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
    	
List<T>會從第一個項目開始向前搜尋，並結束於最後一個專案。


Predicate<T>是方法的委派，如果傳遞至該方法的物件符合委派中定義的條件，則會傳回 true 。  目前 List<T> 的專案會個別傳遞至 Predicate<T> 委派。 委派具有簽章：


public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法會執行線性搜尋;因此，這個方法是 o (n) 作業，其中 n 是 Count。

	
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

    	
下列範例會定義具有兩個 Employee 欄位 Name 和 Id的類別。 它也會使用單一 EmployeeSearch 方法定義類別， StartsWith指出欄位是否 Employee.Name 以提供給類別建構函式的 EmployeeSearch 指定子字串開頭。 請注意此方法的簽章


public bool StartsWith(Employee e)

Public Function StartsWith(e As Employee) As Boolean

會對應至可以傳遞至 方法之委派的 FindIndex 簽章。 此範例會具現化 物件、將一些Employee物件加入其中，然後呼叫 FindIndex(Int32, Int32, Predicate<T>) 方法兩次，從其第五個List<Employee>成員開始搜尋集合 (，也就是索引 4) 的成員。 第一次，它會搜尋欄位開頭為 “J” 的第一個 Employee 物件 Name ;第二次，它會搜尋字段開頭為 “Ju” 的第一個 Employee 物件 Name 。


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
    	
List<T>會從 最後startIndex一個元素開始和結束搜尋。


Predicate<T>是方法的委派，如果傳遞至該方法的物件符合委派中定義的條件，則會傳回 true 。  目前 List<T> 的專案會個別傳遞至 Predicate<T> 委派。 委派具有簽章：


public bool methodName(T obj)

Public Function methodName(obj As T) As Boolean

此方法會執行線性搜尋;因此，此方法是 O (n) 作業，其中 n 是 從 startIndex 到 結尾的項目 List<T>數目。

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