Comparison<T> Delegate
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Represents the method that compares two objects of the same type.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Delegate Function Comparison(Of In T) ( _
x As T, _
y As T _
) As Integer
public delegate int Comparison<in T>(
T x,
T y
)
Type Parameters
inT
The type of the objects to compare.This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see 2678dc63-c7f9-4590-9ddc-0a4df684d42e.
Parameters
- x
Type: T
The first object to compare.
- y
Type: T
The second object to compare.
Return Value
Type: System.Int32
A signed integer that indicates the relative values of x and y, as shown in the following table.
Value |
Condition |
|---|---|
Less than 0 |
x is less than y. |
0 |
x equals y. |
Greater than 0 |
x is greater than y. |
Remarks
This delegate is used by the Sort<T>(array<T[], Comparison<T>) method overload of the Array class and the Sort(Comparison<T>) method overload of the List<T> class to sort the elements of an array or list.
Examples
The following code example demonstrates the use of the Comparison<T> delegate with the Sort(Comparison<T>) method overload.
The code example defines an alternative comparison method for strings, named CompareDinosByLength. This method works as follows: First, the comparands are tested for nulla null reference (Nothing in Visual Basic), and a null reference is treated as less than a non-null. Second, the string lengths are compared, and the longer string is deemed to be greater. Third, if the lengths are equal, ordinary string comparison is used.
A List<T> of strings is created and populated with four strings, in no particular order. The list also includes an empty string and a null reference. The list is displayed, sorted using a Comparison<T> generic delegate representing the CompareDinosByLength method, and displayed again.
.gif "Note") Note: |
|---|
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control. |
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 Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
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(outputBlock, dinosaurs)
outputBlock.Text &= vbLf & "Sort with generic Comparison(Of String) delegate:" & vbCrLf
dinosaurs.Sort(AddressOf CompareDinosByLength)
Display(outputBlock, dinosaurs)
End Sub
Private Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal lis As List(Of String))
outputBlock.Text &= vbCrLf
For Each s As String In lis
If s Is Nothing Then
outputBlock.Text &= "(Nothing)" & vbCrLf
Else
outputBlock.Text += String.Format("""{0}""", s) & vbCrLf
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"
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 Demo(System.Windows.Controls.TextBlock outputBlock)
{
List<string> dinosaurs = new List<string>();
dinosaurs.Add("Pachycephalosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("");
dinosaurs.Add(null);
dinosaurs.Add("Mamenchisaurus");
dinosaurs.Add("Deinonychus");
Display(outputBlock, dinosaurs);
outputBlock.Text += "\nSort with generic Comparison<string> delegate:" + "\n";
dinosaurs.Sort(CompareDinosByLength);
Display(outputBlock, dinosaurs);
}
private static void Display(System.Windows.Controls.TextBlock outputBlock, List<string> list)
{
outputBlock.Text += "\n";
foreach (string s in list)
{
if (s == null)
outputBlock.Text += "(null)" + "\n";
else
outputBlock.Text += String.Format("\"{0}\"", s) + "\n";
}
}
}
/* This code example produces the following output:
"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"
Sort with generic Comparison<string> delegate:
(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.