Lesson 09.1 – Using your classes as datatypes

Lesson Objectives

At the end of this lesson, you will know…

• How to create a property in a class that uses one of your other classes as its datatype.

Adding properties with custom datatypes

Currently, all of the properties in our classes are either strings or integers. But sometimes we need to store something more complex in a property.

For example, in the Location class, we want to possibly store an item required to enter the location (such as a key). If there is a quest available at that location, we need to store that value. We also might have a monster that exists in that location.

So we need to add some new properties to the Location class, to store these values.

Link to video on YouTube

Step 1: Start Visual Studio Express 2013 for Desktop, and open the solution.

Step 2: Edit the Location class, in the Engine project. Add these new properties:

        public Item ItemRequiredToEnter { get; set; }
        public Quest QuestAvailableHere { get; set; }
        public Monster MonsterLivingHere { get; set; }
        public Location LocationToNorth { get; set; }
        public Location LocationToEast { get; set; }
        public Location LocationToSouth { get; set; }
        public Location LocationToWest { get; set; }

Now we have properties to hold these values for each location. Because we need to store an Item object in the ItemRequiredToEnter property, its datatype is Item. Just like using a string datatype when we want to store some text in a property.

Step 3: Now, let’s add parameters to the constructor to accept some of these values and save them to the properties. Change the constructor code to this:

public Location(int id, string name, string description, Item itemRequiredToEnter = null, Quest questAvailableHere = null, Monster monsterLivingHere = null)
{
    ID = id;
    Name = name;
    Description = description;
    ItemRequiredToEnter = itemRequiredToEnter;
    QuestAvailableHere = questAvailableHere;
    MonsterLivingHere = monsterLivingHere;
}

Notice that after each of the new parameters, there is ” = null”. Some locations won’t have an item required to enter them, a quest available at them, or a monster living there. This lets us call the Location constructor without passing these three values. The constructor will know to use the default values, which, in this case, is the “null”. So, both of these lines would work the same way:

Location test1 = new Location(1, "Your House", "This is your house");
Location test2 = new Location(1, "Your House", "This is your house", null, null, null);

Step 4: Edit the Quest class, in the Engine project. Add this new property:

public Item RewardItem { get; set; }

The RewardItem property will store what item the player receives when they complete the quest.

NOTE: In the video, the parameters in the Location class constructor are on two lines now, and that’s OK. Since the last character of the first line is a comma, the computer knows that the next line is a continuation of the first line. I just did this because that line was getting long, and a little difficult to read.

In C#, the end of a line is signified by a semi-colon “;”, a closing parentheses “)”, or a closing bracket “}”.

Summary

Now you can create properties that hold more complex values. This way, you’ll be able to do things such as get the name of the monster at the location, without needing to do extra lookups somewhere outside of your object.

Source code for this lesson

Source code on GitHub

Source code on DropBox

Next lesson: Lesson 10.1 – Creating collections of objects

Previous lesson: Lesson 08.2 – Using class constructors with derived classes

All lessons: Learn C# by Building a Simple RPG Index