Collectibles, Inventory, and Scoring Systems

# CHAPTER 13

Collectibles, Inventory, and Scoring Systems #

1. Introduction #

2. Learning Objectives #

• Architect a centralized data tracking script (Game Manager).

• Create collectible items that destroy themselves upon pickup.

• Implement a basic List-based inventory system.

• Persistently save and load data using PlayerPrefs.

• Create a High Score system that survives game reboots.

3. The Data Manager Architecture #

• Bad Idea: Putting it on the Coin script. If you collect the coin and destroy it, the score is destroyed!

• Bad Idea: Putting it on the Player script. If the player falls in lava and is destroyed/respawned, the score is lost!

• Good Idea: Create an Empty GameObject called GameManager. Attach a script to it that holds the score. It acts as an independent referee overseeing the match.

public class GameManager : MonoBehaviour
{
    public int currentScore = 0;
    public TextMeshProUGUI scoreText;

    public void AddPoints(int amount)
    {
        currentScore += amount;
        scoreText.text = "Score: " + currentScore;
    }
}

4. Creating the Collectible #

public class CoinPickup : MonoBehaviour
{
    // Drag the GameManager object into this slot in the Inspector
    public GameManager manager; 

    void OnTriggerEnter(Collider other)
    {
        if (other.CompareTag("Player"))
        {
            manager.AddPoints(10); // Give the player 10 points
            Destroy(gameObject);   // Vanish!
        }
    }
}

5. Basic Inventory (Lists) #

using System.Collections.Generic; // Required for Lists!

public class InventoryManager : MonoBehaviour
{
    public List<string> backpack = new List<string>();

    public void AddItem(string itemName)
    {
        backpack.Add(itemName);
        Debug.Log("Added " + itemName + " to backpack. Total items: " + backpack.Count);
    }
}

6. Saving Data (PlayerPrefs) #

• PlayerPrefs.SetInt("HighScore", 500) -> Saves the number to the hard drive.

• PlayerPrefs.GetInt("HighScore", 0) -> Reads the number from the hard drive (and defaults to 0 if the file doesn't exist yet).

7. The High Score System #

public void CheckHighScore()
{
    // 1. Load the old high score from the hard drive
    int savedHighScore = PlayerPrefs.GetInt("HighScore", 0);

    // 2. Did we beat it?
    if (currentScore > savedHighScore)
    {
        // 3. Save the new high score!
        PlayerPrefs.SetInt("HighScore", currentScore);
        PlayerPrefs.Save(); // Force write to disk
        Debug.Log("NEW HIGH SCORE: " + currentScore);
    }
}

8. Visual Learning: The Collection Pipeline #

[ Player touches Coin Collider (Trigger) ]
         |
[ Coin script calls manager.AddPoints(10) ]
         |
[ Coin calls Destroy(gameObject) ] 
         |
[ GameManager increases 'score' var in RAM ]
         |
[ GameManager updates UI Text on Canvas ]
         |
[ On Game Over, GameManager writes score to PlayerPrefs (Hard Drive) ]

9. Best Practices #

• PlayerPrefs is for Simple Data Only: PlayerPrefs is perfect for saving volume settings, level unlocks, and high scores. However, it is easily hackable by players and slow for massive data. If you are building a massive Skyrim-style RPG with 1,000 inventory items, you should learn to save data using JSON serialization instead.

10. Common Mistakes #

• NullReferenceExceptions: The most common error in this workflow is forgetting to drag the GameManager object into the manager slot on your Coin prefab's Inspector. If the Coin tries to run manager.AddPoints(10) but the slot is empty, the game will crash and scream NullReferenceException: Object reference not set to an instance of an object.

11. Mini Project: Build an RPG Key/Door System #

1. 1. Create a GameManager script with a public bool hasRedKey = false;.

1. 2. Create a small red cube (The Key). Set it to Is Trigger.

1. 3. Write a script on the Key: OnTriggerEnter -> set manager.hasRedKey = true -> Destroy(gameObject).

1. 4. Create a large brown cube (The Door). Set it to solid (not trigger).

1. 5. Write a script on the Door using OnCollisionEnter:

void OnCollisionEnter(Collision hit)
{
    if (hit.gameObject.CompareTag("Player"))
    {
        // Check if the manager says we have the key!
        if (manager.hasRedKey == true)
        {
            Debug.Log("Door Unlocked!");
            Destroy(gameObject); // Open the door!
        }
        else
        {
            Debug.Log("The door is locked. Find the red key.");
        }
    }
}

12. Practice Exercises #

1. 1. Why is it architecturally dangerous to store the player's total score variable directly on the Player's movement script?

1. 2. What C# collection type is best suited for an RPG inventory where items are constantly being added and removed?

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain the decoupling architecture of using a centralized GameManager for scoring versus storing data locally on pickups or the player character.

• Q: Describe the limitations of PlayerPrefs. Provide a scenario where PlayerPrefs is the perfect tool, and a scenario where JSON serialization must be used instead.

• Q: Walk me through the exact logic required to check an active score against a saved high score, update it if necessary, and ensure the data is written to the hard drive.

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #