Comparison<T> Delegate
Represents the method that compares two objects of the same type.
Assembly: mscorlib (in mscorlib.dll)
Type Parameters
- in T
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 Covariance and Contravariance in Generics.
Parameters
- x
- Type: T
The first object to compare.
- y
- Type: T
The second object to compare.
Return Value
Type: System.Int32A signed integer that indicates the relative values of x and y, as shown in the following table.
Value | Meaning |
|---|---|
Less than 0 | x is less than y. |
0 | x equals y. |
Greater than 0 | x is greater than y. |
This delegate is used by the Sort<T>(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.
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 null, 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.
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" */
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
- 2/23/2011
- FrustratedWithCrappyDocs
