List<> question

[Hurraa]

Hello,

when you create a new List for example:

List<BaseClass> m_list = new List<BaseClass>();

can you add the Class

public SubClass : BaseClass
{
 ....
}

to the List?

m_list.Add(new Subclass());

thx

[Greystar]

C# Lists: Add some elegance to your code

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.

Maybe that will be helpful.

[Suil Ban]

Originally Posted by Hurraa

Hello,

when you create a new List for example:

List<BaseClass> m_list = new List<BaseClass>();

can you add the Class

public SubClass : BaseClass
{
 ....
}

to the List?

m_list.Add(new Subclass());

thx

Yes, this will work just fine.

[DragonBoy]

Originally Posted by Hurraa

Hello,

when you create a new List for example:

List<BaseClass> m_list = new List<BaseClass>();

can you add the Class

public SubClass : BaseClass
{
 ....
}

to the List?

m_list.Add(new Subclass());

thx

Simple answer: Yes

SubClass is BaseClass so it can be used as BaseClass if casted correctly. However, it will be BaseClass so I am not entirely sure what the point would be.

[Ravenal]

ReadItem<T>() where T : Item

Directly from the Core this represents that if it is based then when you do someting like

reader.ReadItem<MyItem>(); it'll reference MyItem etc.

Its the same thing with BaseClasses and SubClasses... I have a good example of this as I hold two different types of Dictionary based

Dictionary<ManagerGroup, DirectoryInfo>

Where I can store my GManagerGroup because it's parent class is ManagerGroup

Now if you need to get something of that source then you will need to do something like

List<Item> items = new List<Item>();

items.Add( new Gold(1000) );

you then can reference 'if ( items[i] is Gold ) do something'...

It is highly recommended to always to use the actual class that your going to store data in there, if your storing multiple "SubClasses" in a List then using BaseClass would be the best...

Example:

IF I am only storing Gold into a list then I will want to create
List<Gold> goldpiles = new List<Gold>();

now if I need to store Gold, Gems, and Jewelry then Its best to reference "Item" in the list...