Comparison<T> Delegar

Definição

generic <typename T>
public delegate int Comparison(T x, T y);

public delegate int Comparison<in T>(T x, T y);

public delegate int Comparison<in T>(T x, T y) where T : allows ref struct;

public delegate int Comparison<T>(T x, T y);

type Comparison<'T> = delegate of 'T * 'T -> int

Public Delegate Function Comparison(Of In T)(x As T, y As T) As Integer 

Public Delegate Function Comparison(Of T)(x As T, y As T) As Integer 

Parâmetros de Tipo Genérico

Parâmetros

Devolver Valor

Um inteiro com sinal que indica os valores relativos de x e y, conforme mostrado na tabela seguinte.

Exemplos

O exemplo de código seguinte demonstra o uso do Comparison<T> delegado com a Sort(Comparison<T>) sobrecarga de métodos.

O exemplo de código define um método alternativo de comparação para cadeias, chamado CompareDinosByLength. Este método funciona da seguinte forma: Primeiro, os comparandos são testados para null, e uma referência nula é tratada como menor do que uma não-nula. Em segundo lugar, os comprimentos das cordas são comparados, e a corda mais longa é considerada maior. Terceiro, se os comprimentos forem iguais, utiliza-se a comparação de cordas ordinária.

A List<T> de cordas é criado e povoado com quatro cadeias, sem ordem específica. A lista inclui também uma cadeia vazia e uma referência nula. A lista é exibida, ordenada usando um Comparison<T> delegado genérico que representa o CompareDinosByLength método, e novamente apresentada.

using System;
using System.Collections.Generic;

public class Example
{
    private static int CompareDinosByLength(string x, string y)
    {
        if (x == null)
        {
            if (y == null)
            {
                // If x is null and y is null, they're
                // equal.
                return 0;
            }
            else
            {
                // If x is null and y is not null, y
                // is greater.
                return -1;
            }
        }
        else
        {
            // If x is not null...
            //
            if (y == null)
                // ...and y is null, x is greater.
            {
                return 1;
            }
            else
            {
                // ...and y is not null, compare the
                // lengths of the two strings.
                //
                int retval = x.Length.CompareTo(y.Length);

                if (retval != 0)
                {
                    // If the strings are not of equal length,
                    // the longer string is greater.
                    //
                    return retval;
                }
                else
                {
                    // If the strings are of equal length,
                    // sort them with ordinary string comparison.
                    //
                    return x.CompareTo(y);
                }
            }
        }
    }

    public static void Main()
    {
        List<string> dinosaurs = new List<string>();
        dinosaurs.Add("Pachycephalosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("");
        dinosaurs.Add(null);
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Deinonychus");
        Display(dinosaurs);

        Console.WriteLine("\nSort with generic Comparison<string> delegate:");
        dinosaurs.Sort(CompareDinosByLength);
        Display(dinosaurs);
    }

    private static void Display(List<string> list)
    {
        Console.WriteLine();
        foreach( string s in list )
        {
            if (s == null)
                Console.WriteLine("(null)");
            else
                Console.WriteLine("\"{0}\"", s);
        }
    }
}

/* This code example produces the following output:

"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"

Sort with generic Comparison<string> delegate:

(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
 */

open System

let compareDinosByLength (x: string) (y: string) =
    match x with 
    | null when isNull y ->
        // If x is null and y is null, they're equal.
        0
    | null ->
        // If x is null and y is not null, y is greater.
        -1
    | _ when isNull y->
        // If x is not null and y is null, x is greater.
        1
    | _ ->
        // If x is not null and y is not null, compare the lengths of the two strings.
        let retval = x.Length.CompareTo y.Length

        if retval <> 0 then
            // If the strings are not of equal length, the longer string is greater.
            retval
        else
            // If the strings are of equal length, sort them with ordinary string comparison.
            x.CompareTo y

let display list =
    printfn ""
    for s in list do
        if isNull s then
            printfn "(null)"
        else
            printfn $"\"%s{s}\""


let dinosaurs = ResizeArray()
dinosaurs.Add "Pachycephalosaurus"
dinosaurs.Add "Amargasaurus"
dinosaurs.Add ""
dinosaurs.Add null
dinosaurs.Add "Mamenchisaurus"
dinosaurs.Add "Deinonychus"
display dinosaurs

printfn "\nSort with generic Comparison<string> delegate:"
dinosaurs.Sort compareDinosByLength
display dinosaurs


// This code example produces the following output:
//
// "Pachycephalosaurus"
// "Amargasaurus"
// ""
// (null)
// "Mamenchisaurus"
// "Deinonychus"
//
// Sort with generic Comparison<string> delegate:
//
// (null)
// ""
// "Deinonychus"
// "Amargasaurus"
// "Mamenchisaurus"
// "Pachycephalosaurus"

Imports System.Collections.Generic

Public Class Example

    Private Shared Function CompareDinosByLength( _
        ByVal x As String, ByVal y As String) As Integer

        If x Is Nothing Then
            If y Is Nothing Then 
                ' If x is Nothing and y is Nothing, they're
                ' equal. 
                Return 0
            Else
                ' If x is Nothing and y is not Nothing, y
                ' is greater. 
                Return -1
            End If
        Else
            ' If x is not Nothing...
            '
            If y Is Nothing Then
                ' ...and y is Nothing, x is greater.
                Return 1
            Else
                ' ...and y is not Nothing, compare the 
                ' lengths of the two strings.
                '
                Dim retval As Integer = _
                    x.Length.CompareTo(y.Length)

                If retval <> 0 Then 
                    ' If the strings are not of equal length,
                    ' the longer string is greater.
                    '
                    Return retval
                Else
                    ' If the strings are of equal length,
                    ' sort them with ordinary string comparison.
                    '
                    Return x.CompareTo(y)
                End If
            End If
        End If

    End Function

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)
        dinosaurs.Add("Pachycephalosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("")
        dinosaurs.Add(Nothing)
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Deinonychus")
        Display(dinosaurs)

        Console.WriteLine(vbLf & "Sort with generic Comparison(Of String) delegate:")
        dinosaurs.Sort(AddressOf CompareDinosByLength)
        Display(dinosaurs)

    End Sub

    Private Shared Sub Display(ByVal lis As List(Of String))
        Console.WriteLine()
        For Each s As String In lis
            If s Is Nothing Then
                Console.WriteLine("(Nothing)")
            Else
                Console.WriteLine("""{0}""", s)
            End If
        Next
    End Sub
End Class

' This code example produces the following output:
'
'"Pachycephalosaurus"
'"Amargasaurus"
'""
'(Nothing)
'"Mamenchisaurus"
'"Deinonychus"
'
'Sort with generic Comparison(Of String) delegate:
'
'(Nothing)
'""
'"Deinonychus"
'"Amargasaurus"
'"Mamenchisaurus"
'"Pachycephalosaurus"

O exemplo seguinte usa o Comparison<T> delegado para ordenar os elementos de uma coleção de CityInfo objetos. CityInfo é uma classe definida pela aplicação que contém informações sobre uma cidade e a sua população. O exemplo define três métodos, CompareByName, CompareByPopulation, e CompareByNames, que oferecem três formas diferentes de ordenar os CityInfo objetos. Cada método é atribuído ao comparison argumento do Array.Sort<T>(T[], Comparison<T>) método.

using System;

public class CityInfo
{
   string cityName;
   string countryName;
   int pop2010;

   public CityInfo(string name, string country, int pop2010)
   {
      this.cityName = name;
      this.countryName = country;
      this.pop2010 = pop2010;
   }

   public string City
   { get { return this.cityName; } }

   public string Country
   { get { return this.countryName; } }

   public int Population
   { get { return this.pop2010; } }

   public static int CompareByName(CityInfo city1, CityInfo city2)
   {
      return String.Compare(city1.City, city2.City);
   }

   public static int CompareByPopulation(CityInfo city1, CityInfo city2)
   {
      return city1.Population.CompareTo(city2.Population);
   }

   public static int CompareByNames(CityInfo city1, CityInfo city2)
   {
      return String.Compare(city1.Country + city1.City, city2.Country + city2.City);
   }
}

public class Example
{
   public static void Main()
   {
      CityInfo NYC = new CityInfo("New York City", "United States of America", 8175133 );
      CityInfo Det = new CityInfo("Detroit", "United States of America", 713777);
      CityInfo Paris = new CityInfo("Paris", "France",  2193031);
      CityInfo[] cities = { NYC, Det, Paris };
      // Display ordered array.
      DisplayArray(cities);

      // Sort array by city name.
      Array.Sort(cities, CityInfo.CompareByName);
      DisplayArray(cities);

      // Sort array by population.
      Array.Sort(cities, CityInfo.CompareByPopulation);
      DisplayArray(cities);

      // Sort array by country + city name.
      Array.Sort(cities, CityInfo.CompareByNames);
      DisplayArray(cities);
   }

   private static void DisplayArray(CityInfo[] cities)
   {
      Console.WriteLine("{0,-20} {1,-25} {2,10}", "City", "Country", "Population");
      foreach (var city in cities)
         Console.WriteLine("{0,-20} {1,-25} {2,10:N0}", city.City,
                           city.Country, city.Population);

      Console.WriteLine();
   }
}
// The example displays the following output:
//     City                 Country                   Population
//     New York City        United States of America   8,175,133
//     Detroit              United States of America     713,777
//     Paris                France                     2,193,031
//
//     City                 Country                   Population
//     Detroit              United States of America     713,777
//     New York City        United States of America   8,175,133
//     Paris                France                     2,193,031
//
//     City                 Country                   Population
//     Detroit              United States of America     713,777
//     Paris                France                     2,193,031
//     New York City        United States of America   8,175,133
//
//     City                 Country                   Population
//     Paris                France                     2,193,031
//     Detroit              United States of America     713,777
//     New York City        United States of America   8,175,133

open System

type CityInfo =
    { City: string
      Country: string
      Population: int }

    static member CompareByName city1 city2 =
        String.Compare(city1.City, city2.City)

    static member CompareByPopulation city1 city2 =
        city1.Population.CompareTo city2.Population 

    static member CompareByNames city1 city2 =
        String.Compare(city1.Country + city1.City, city2.Country + city2.City)

let display cities =
    printfn $"""{"City",-20} {"Country",-25} {"Population",10}"""
    for city in cities do
        printfn $"{city.City,-20} {city.Country,-25} {city.Population,10:N0}"
    printfn ""

let NYC = { City = "New York City"; Country = "United States of America"; Population = 8175133 }
let Det = { City = "Detroit"; Country = "United States of America"; Population = 713777 }
let Paris = { City = "Paris"; Country = "France"; Population = 2193031 }
let cities = [| NYC; Det; Paris |]
// Display ordered array.
display cities

// Sort array by city name.
Array.Sort(cities, CityInfo.CompareByName)
display cities

// Sort array by population.
Array.Sort(cities, CityInfo.CompareByPopulation);
display cities

// Sort array by country + city name.
Array.Sort(cities, CityInfo.CompareByNames);
display cities


// The example displays the following output:
//     City                 Country                   Population
//     New York City        United States of America   8,175,133
//     Detroit              United States of America     713,777
//     Paris                France                     2,193,031
//
//     City                 Country                   Population
//     Detroit              United States of America     713,777
//     New York City        United States of America   8,175,133
//     Paris                France                     2,193,031
//
//     City                 Country                   Population
//     Detroit              United States of America     713,777
//     Paris                France                     2,193,031
//     New York City        United States of America   8,175,133
//
//     City                 Country                   Population
//     Paris                France                     2,193,031
//     Detroit              United States of America     713,777
//     New York City        United States of America   8,175,133

Public Class CityInfo
   Dim cityName As String
   Dim countryName As String
   Dim pop2010 As Integer
   
   Public Sub New(name As String, country As String, pop2010 As Integer)
      Me.cityName = name
      Me.countryName = country
      Me.pop2010 = pop2010
   End Sub
   
   Public ReadOnly Property City As String
      Get
         Return Me.cityName
      End Get
   End Property
   
   Public ReadOnly Property Country As String
      Get
         Return Me.countryName
      End Get
   End Property
   
   Public ReadOnly Property Population As Integer
      Get
         Return Me.pop2010
      End Get   
   End Property
   
   Public Shared Function CompareByName(city1 As CityInfo, city2 As CityInfo) As Integer
      Return String.Compare(city1.City, city2.City)
   End Function
   
   Public Shared Function CompareByPopulation(city1 As CityInfo, city2 As CityInfo) As Integer
      Return city1.Population.CompareTo(city2.Population)
   End Function
   
   Public Shared Function CompareByNames(city1 As CityInfo, city2 As CityInfo) As Integer
      Return String.Compare(city1.Country + city1.City, city2.Country + city2.City)
   End Function   
End Class

Module Example
   Public Sub Main()
      Dim NYC As New CityInfo("New York City", "United States of America", 8175133)
      Dim Det As New CityInfo("Detroit", "United States of America", 713777)
      Dim Paris As New CityInfo("Paris", "France", 2193031)
      Dim cities As CityInfo() = { NYC, Det, Paris }
      ' Display ordered array.
      DisplayArray(cities)
      
      ' Sort array by city name.
      Array.Sort(cities, AddressOf CityInfo.CompareByName)
      DisplayArray(cities)
      
      ' Sort array by population.
      Array.Sort(cities, AddressOf CityInfo.CompareByPopulation)
      DisplayArray(cities)
      
      ' Sort array by country + city name.
      Array.Sort(cities, AddressOf CityInfo.CompareByNames)
      DisplayArray(cities)
   End Sub
   
   Private Sub DisplayArray(cities() As CityInfo)
      Console.WriteLine("{0,-20} {1,-25} {2,10}", "City", "Country/Region", "Population")
      For Each city In cities
         Console.WriteLine("{0,-20} {1,-25} {2,10:N0}", city.City, city.Country, city.Population)
      Next
      Console.WriteLine()
   End Sub
End Module
' The example displays the following output:
'     City                 Country/Region            Population
'     New York City        United States of America   8,175,133
'     Detroit              United States of America     713,777
'     Paris                France                     2,193,031
'     
'     City                 Country/Region            Population
'     Detroit              United States of America     713,777
'     New York City        United States of America   8,175,133
'     Paris                France                     2,193,031
'     
'     City                 Country/Region            Population
'     Detroit              United States of America     713,777
'     Paris                France                     2,193,031
'     New York City        United States of America   8,175,133
'     
'     City                 Country/Region            Population
'     Paris                France                     2,193,031
'     Detroit              United States of America     713,777
'     New York City        United States of America   8,175,133

Observações

Este delegado é usado pela Sort<T>(T[], Comparison<T>) sobrecarga de métodos da Array classe e pela Sort(Comparison<T>) sobrecarga de métodos da List<T> classe para ordenar os elementos de um array ou lista.

Ver também

• Sort<T>(T[], Comparison<T>)
• Sort(Comparison<T>)