C# 4 and .NET 4

138 ❘ ChaPTer 6 ArrAys And tuples
should be compared. The IComparer interface is independent of the class to compare. That’s why the
Compare() method defines two arguments that should be compared. The return value is similar to the
CompareTo() method of the IComparable interface.
The class PersonComparer implements the IComparer interface to sort Person objects either by
firstName or by lastName The enumeration PersonCompareType defines the different sorting options
that are available with the PersonComparer: FirstName and LastName. How the compare should happen
is defined with the constructor of the class PersonComparer where a PersonCompareType value is set. The
Compare() method is implemented with a switch statement to compare either by LastName or
by FirstName.
public enum PersonCompareType
{
FirstName,
LastName
}
public class PersonComparer: IComparer
{
private PersonCompareType compareType;
public PersonComparer(PersonCompareType compareType)
{
this.compareType = compareType;
}
public int Compare(Person x, Person y)
{
if (x == null) throw new ArgumentNullException("x");
if (y == null) throw new ArgumentNullException("y");
}
}
switch (compareType)
{
case PersonCompareType.FirstName:
return x.FirstName.CompareTo(y.FirstName);
case PersonCompareType.LastName:
return x.LastName.CompareTo(y.LastName);
default:
throw new ArgumentException(
"unexpected compare type");
}
code snippet SortingSample/PersonComparer.cs
Now you can pass a PersonComparer object to the second argument of the Array.Sort() method. Here
the persons are sorted by first name:
Array.Sort(persons,
new PersonComparer(PersonCompareType.FirstName));
foreach (var p in persons)
{
Console.WriteLine(p);
}
code snippet SortingSample/Program.cs
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