It is a fairly common programming scenario to find ourselves with a list of identical objects. In the past, without adequate support from programming languages, we found ourselves writing a lot of searching and sorting code, and that may have put you off using lists in favour of arrays. All that has changed with C# (particularly 2.0) - its implementation of a list makes handling such lists remarkably easy.
For example, given the following class Person:
public
class Person
{
?????????
public
int age;
?????????
public
string name;
?????????
public Person(int age, string name)
????????? {
??????????????????
this.age = age;
??????????????????
this.name = name;
????????? }
}
We can create a list of Person objects and add six people like so:
List<person>people =
new
List<person>();people.Add(
new
Person(50, "Fred"));
people.Add(
new
Person(30, "John"));
people.Add(
new
Person(26, "Andrew"));
people.Add(
new
Person(24, "Xavier"));
people.Add(
new
Person(5, "Mark"));
people.Add(
new
Person(6, "Cameron"));
C#'s list mechanism provides us with a number of useful methods. Personally, I find ForEach, FindAll and Sort to be very useful. ForEach allows us access to each item in the list. FindAll allows us to search for objects in the list that match a specific condition. Sort allows us to sort the objects in the list. The following code demonstrates how we might use each of these methods:
Console.WriteLine("Unsorted list");
people.ForEach(
delegate
(Person p)
?? { Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Find the young
List<person> young = people.FindAll(
delegate
(Person p) {
return
p.age < 25; });
Console.WriteLine("Age
is
less than 25");
young.ForEach(
delegate
(Person p)
?? { Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Sort by name
Console.WriteLine("Sorted list, by name");
people.Sort(
delegate
(Person p1, Person p2)
?? {
return
p1.name.CompareTo(p2.name); });people.ForEach(
delegate
(Person p)
?? { Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
// Sort by age
Console.WriteLine("Sorted list, by age");people.Sort(
delegate
(Person p1, Person p2)
?? {
return
p1.age.CompareTo(p2.age); });people.ForEach(
delegate
(Person p)
?? { Console.WriteLine(String.Format("{0} {1}", p.age, p.name)); });
And here is the output that we should expect:
Unsorted list
50 Fred
30 John
26 Andrew
24 Xavier
5 Mark
6 Cameron
Age is less than 25
24 Xavier
5 Mark
6 Cameron
Sorted list, by name
26 Andrew
6 Cameron
50 Fred
30 John
5 Mark
24 Xavier
Sorted list, by age
5 Mark
6 Cameron
24 Xavier
26 Andrew
30 John
50 Fred
Lists are powerful and result in fewer, and more elegant, lines of code. Hopefully this short example has demonstrated their ease and you will find yourself using them in your day-to-day development activities.