This browser is no longer supported.

Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.

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

Parameters

startIndex is outside the range of valid indexes for the List<T> .

count is less than 0.

startIndex and count do not specify a valid section in the List<T> .

Examples

The following example defines an Employee class with two fields, Name and Id . It also defines an EmployeeSearch class with a single method, StartsWith , that indicates whether the Employee.Name field starts with a specified substring that is supplied to the EmployeeSearch class constructor. Note the signature of this method

public bool StartsWith(Employee e)
Public Function StartsWith(e As Employee) As Boolean
corresponds to the signature of the delegate that can be passed to the FindIndex method. The example instantiates a List<Employee> object, adds a number of Employee objects to it, and then calls the FindIndex(Int32, Int32, Predicate<T>) method twice to search the entire collection (that is, the members from index 0 to index Count - 1). The first time, it searches for the first Employee object whose Name field begins with "J"; the second time, it searches for the first Employee object whose Name field begins with "Ju".
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
    	
Remarks
    	
The List<T> is searched forward starting at startIndex and ending at startIndex plus count minus 1, if count is greater than 0.
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.  The elements of the current List<T> are individually passed to the Predicate<T> delegate. The delegate has the signature:
public bool methodName(T obj)
Public Function methodName(obj As T) As Boolean
This method performs a linear search; therefore, this method is an O(n) operation, where n is 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
	
Parameters
  
Examples
    	
The following example defines an Employee class with two fields, Name and Id. It also defines an EmployeeSearch class with a single method, StartsWith, that indicates whether the Employee.Name field starts with a specified substring that is supplied to the EmployeeSearch class constructor. Note  the signature of this method
public bool StartsWith(Employee e)
Public Function StartsWith(e As Employee) As Boolean
corresponds to the signature of the delegate that can be passed to the FindIndex method. The example instantiates a List<Employee> object, adds a number of Employee objects to it, and then calls the FindIndex(Int32, Int32, Predicate<T>) method twice to search the entire collection, the first time for the first Employee object whose Name field begins with "J", and the second time for the first Employee object whose Name field begins with "Ju".
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
    	
Remarks
    	
The List<T> is searched forward starting at the first element and ending at the last element.
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.  The elements of the current List<T> are individually passed to the Predicate<T> delegate. The delegate has the signature:
public bool methodName(T obj)
Public Function methodName(obj As T) As Boolean
This method performs a linear search; therefore, this method is an O(n) operation, where n is 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
	
Parameters
  
Examples
    	
The following example defines an Employee class with two fields, Name and Id. It also defines an EmployeeSearch class with a single method, StartsWith, that indicates whether the Employee.Name field starts with a specified substring that is supplied to the EmployeeSearch class constructor. Note  the signature of this method
public bool StartsWith(Employee e)
Public Function StartsWith(e As Employee) As Boolean
corresponds to the signature of the delegate that can be passed to the FindIndex method. The example instantiates a List<Employee> object, adds a number of Employee objects to it, and then calls the FindIndex(Int32, Int32, Predicate<T>) method twice to search the collection starting with its fifth member (that is, the member at index 4). The first time, it searches for the first Employee object whose Name field begins with "J"; the second time, it searches for the first Employee object whose Name field begins with "Ju".
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
    	
Remarks
    	
The List<T> is searched forward starting at startIndex and ending at the last element.
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.  The elements of the current List<T> are individually passed to the Predicate<T> delegate. The delegate has the signature:
public bool methodName(T obj)
Public Function methodName(obj As T) As Boolean
This method performs a linear search; therefore, this method is an O(n) operation, where n is the number of elements from startIndex to the end of the List<T>.
			Coming soon: Throughout 2024 we will be phasing out GitHub Issues as the feedback mechanism for content and replacing it with a new feedback system. For more information see: https://aka.ms/ContentUserFeedback.

        
Submit and view feedback for
                    This product