The coin prefab

To make things a little easier, I have already prepared the visual part of our coin. Download Coin.unitypackage and import it into your project:

The coin prefab

Great job! Now we drag the Coin prefab into the Hierarchy view so that we can take a look at it. As mentioned before, I prepared this prefab visually. I have added Sprite Renderer to the game object and linked it with the coin sprite. I have also created a simple spin animation controlled by the Animator. Don't worry about it right now.

Now, you have to pick up from where I finished. Most collectables react with the environment through the physics of the game. We can use the 2D trigger here to react with the Player Game Object Rigidbody2D component. This is the exactly the same way we inserted LeaveTriggers into the game previously.

Select the coin and add the CircleCollider2D component. A green circle will appear around the coin, representing the triggering area. Make sure you tweak the radius value to roughly match the size of the coin. In my case, a value of 0.35 works great.

Another requirement that we need to fulfill to make the trigger work is ticking the IsTrigger checkbox. That's it! Our coin is ready to process trigger events. All that we need to do now is write some code to manage its behavior:

The coin prefab

The Collectable class

Let's plan what behavior we want from our collectable. We will need the following methods:

  • Show(): This will show the coin and activate its collider
  • Hide(): This will hide the coin and deactivate its collider
  • Collect(): This is called at the moment of collection of the coin
  • OnTriggerEnter2D(Collider2D other): This is called by Unity's physics system when the collider enters our coin's trigger

Create a new C# script, call it Collectable, and write the following code:

The Collectable class

Add the Collectable script to your coin prefab. We are ready to test it now! Make the coin prefab a child of one of the level chunks. Create a few copies of the coin next to each other so that you can test them better.

The Collectable class

Let's click on Play in Unity and see what happens. You should notice that the coin disappears upon contact with a Player Game Object. That's exactly what we wanted. Well done!

The last thing to do now is counting the collected coins. We will store the number of coins collected in the GameManager class and increment the int number every time a coin is collected. Let's add some functionality to the GameManager class:

  1. Add the collectedCoins public member:
      public int collectedCoins = 0;
  2. Add a public method that you can call when a coin is collected:
    public void CollectedCoin() {
  collectedCoins ++;
}

    What this method does is increment the collectedCoins variable by 1 every time the ++ operator is used.

  3. In the Collectable class, add a single line calling CollectedCoin() from the Collect method, as follows:
    The Collectable class

Now click on Play in Unity. Let's take a quick look to check whether it works. Select GameManager and press the Play button. You will notice that the number of collected coins in the Unity Inspector increases every time a new coin is collected. Great! We now know that our collectedCoin variable works. However, we still need to update the label value in the gameView so that our user can see exactly how many coins they have collected.

It's a good idea to keep UI-controlling code separate from the GameManager. Let's write a short script that controls the UI on the Game View. Create and add this component to the InGameCanvas game object:

The Collectable class

Once you have the View In Game component added, drag the coinLabel game object into the coinsLabel slot:

The Collectable class

The View In Game component should look like this:

The Collectable class

What our code does is update the .text string value on the label. By doing this, the text on the UI changes and is always up-to-date with the collectedCoins value in Game Manager.

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