Comparison<T> Delegát
Definice
Důležité
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Představuje metodu, která porovnává dva objekty stejného typu.
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<T>(T x, T y);type Comparison<'T> = delegate of 'T * 'T -> intPublic 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 Parametry typu
- T
Typ objektů, které chcete porovnat.
Tento parametr typu je kontravariantní. To znamená, že můžete použít buď zadaný typ, nebo libovolný typ, který je méně odvozený. Další informace o kovarianci a kontravarianci najdete v tématu popisujícím kovarianci a kontravarianci u parametrického polymorfismu.Parametry
- x
- T
První objekt k porovnání
- y
- T
Druhý objekt k porovnání
Návratová hodnota
Celé číslo se znaménkem, které označuje relativní hodnoty x a y, jak je znázorněno v následující tabulce.
| Hodnota | Význam |
|---|---|
| Méně než 0 | x je menší než y.
|
| 0 | xyrovná se .
|
| Větší než 0 | x je větší než y.
|
Příklady
Následující příklad kódu ukazuje použití delegáta Comparison<T> s přetížení metody Sort(Comparison<T>) .
Příklad kódu definuje alternativní metodu porovnání řetězců s názvem CompareDinosByLength. Tato metoda funguje takto: Zaprvé, srovnávací testy jsou testovány pro nulla nulový odkaz je považován za méně než null. Za druhé se porovnávají délky řetězců a delší řetězec se považuje za větší. Zatřetí, pokud jsou délky stejné, použije se běžné porovnání řetězců.
Řetězec List<T> se vytvoří a vyplní čtyřmi řetězci bez konkrétního pořadí. Seznam obsahuje také prázdný řetězec a odkaz na hodnotu null. Zobrazí se seznam seřazený pomocí Comparison<T> obecného delegáta představujícího metodu CompareDinosByLength a zobrazí se znovu.
using namespace System;
using namespace System::Collections::Generic;
int CompareDinosByLength(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// 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 == nullptr)
// ...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);
}
}
}
};
void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
if (s == nullptr)
Console::WriteLine("(null)");
else
Console::WriteLine("\"{0}\"", s);
}
};
void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();
dinosaurs->Add("Pachycephalosaurus");
dinosaurs->Add("Amargasaurus");
dinosaurs->Add("");
dinosaurs->Add(nullptr);
dinosaurs->Add("Mamenchisaurus");
dinosaurs->Add("Deinonychus");
Display(dinosaurs);
Console::WriteLine("\nSort with generic Comparison<String^> delegate:");
dinosaurs->Sort(
gcnew Comparison<String^>(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"
*/
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"
Následující příklad používá delegáta Comparison<T> k řazení prvků kolekce CityInfo objektů. CityInfo je třída definovaná aplikací, která obsahuje informace o městě a jeho populaci. Příklad definuje tři metody, CompareByName, CompareByPopulationa CompareByNames, které nabízejí tři různé způsoby řazení CityInfo objektů. Každá metoda je přiřazena argumentu comparison Array.Sort<T>(T[], Comparison<T>) metody.
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
Poznámky
Tento delegát se používá přetížení Sort<T>(T[], Comparison<T>) Array metody třídy a Sort(Comparison<T>) přetížení List<T> metody třídy k řazení prvků pole nebo seznamu.
Metody rozšíření
| GetMethodInfo(Delegate) |
Získá objekt, který představuje metodu reprezentovanou zadaným delegátem. |