Variables and serialization in Unity - Mini Project: Build & Apply

Variables and Serialization in Unity

📖 Scenario: You are creating a simple Unity game where you want to save the player's name and score so you can load it later.

🎯 Goal: Learn how to create variables and use serialization to save and load player data in Unity.

📋 What You'll Learn

Create variables to store player name and score

Use Unity's serialization to save player data

Load and display saved player data

💡 Why This Matters

🌍 Real World

Saving player data is essential in games to keep progress between sessions.

💼 Career

Understanding variables and serialization is key for game developers working with Unity to manage game state and data persistence.

1

Create player data variables

Create a public class called PlayerData with two public variables: a string called playerName and an int called playerScore.

Unity

public class PlayerData {
    // Your code here
}

Hint

Use public string playerName; and public int playerScore; inside the class.

2

Add serialization attribute

Add the [System.Serializable] attribute above the PlayerData class to enable Unity to serialize it.

Unity

// Add the [System.Serializable] attribute above the PlayerData class
public class PlayerData {
    public string playerName;
    public int playerScore;
}

Hint

Place [System.Serializable] right before public class PlayerData.

3

Create and assign player data instance

In a new GameManager class, create a public variable called playerData of type PlayerData. Then, in the Start() method, first instantiate it with playerData = new PlayerData();, then assign playerData.playerName to "Alex" and playerData.playerScore to 100.

Unity

[System.Serializable]
public class PlayerData {
    public string playerName;
    public int playerScore;
}

public class GameManager : UnityEngine.MonoBehaviour {
    public PlayerData playerData;

    void Start() {
        // Your code here
    }
}

Hint

Declare public PlayerData playerData;, instantiate with playerData = new PlayerData(); and assign values inside Start().

4

Print player data to console

In the Start() method of GameManager, add a Debug.Log statement to print the player's name and score in the format: "Player: Alex, Score: 100".

Unity

[System.Serializable]
public class PlayerData {
    public string playerName;
    public int playerScore;
}

public class GameManager : UnityEngine.MonoBehaviour {
    public PlayerData playerData;

    void Start() {
        playerData = new PlayerData();
        playerData.playerName = "Alex";
        playerData.playerScore = 100;
        // Add Debug.Log to print player data
    }
}

Hint

Use Debug.Log($"Player: {playerData.playerName}, Score: {playerData.playerScore}"); inside Start().

Practice

1. What is the main purpose of serialization in Unity?

easy

A. To convert data into a format that can be saved or sent

B. To create new game objects during runtime

C. To increase the speed of the game

D. To change the color of game objects

Solution

1. Step 1: Recall the definition of serialization

   Serialization means converting data into a format that can be saved or sent.

2. Step 2: Match Unity's use of serialization

   Unity uses serialization to save game data or send it over networks.

3. Final Answer:

   To convert data into a format that can be saved or sent -> Option A

4. Quick Check:

   Serialization = convert data for saving/sending [OK]

Hint: Serialization means saving or sending data format [OK]

Common Mistakes:

• Confusing serialization with creating objects
• Thinking serialization changes game speed
• Mixing serialization with visual changes

2. Which of the following is the correct way to declare a public integer variable in a Unity C# script?

easy

A. int score public;

B. int public score;

C. public int score;

D. public integer score;

Solution

1. Step 1: Recall C# variable declaration syntax

   In C#, access modifier comes first, then type, then variable name.

2. Step 2: Check each option

   public int score; ('public int score;') follows correct order. Options A, B, C have wrong order or wrong type keyword.

3. Final Answer:

   public int score; -> Option C

4. Quick Check:

   Access modifier + type + name = correct declaration [OK]

Hint: Access modifier before type before name in C# [OK]

Common Mistakes:

• Putting 'public' after variable name
• Using 'integer' instead of 'int'
• Incorrect order of keywords

3. What will be the output of this Unity C# code?

using UnityEngine;

public class PlayerData {
    public string playerName = "Alex";
    public int level = 5;
}

public class Test : MonoBehaviour {
    void Start() {
        PlayerData data = new PlayerData();
        string json = JsonUtility.ToJson(data);
        Debug.Log(json);
    }
}

medium

A. Error: JsonUtility.ToJson requires MonoBehaviour

B. {"playerName":Alex,"level":5}

C. {"playerName":"Alex",level:5}

D. {"playerName":"Alex","level":5}

Solution

1. Step 1: Understand JsonUtility.ToJson output format

   JsonUtility converts object fields to JSON string with keys and values in quotes where needed.

2. Step 2: Check the JSON string format

   Strings have quotes, numbers do not. {"playerName":"Alex","level":5} matches correct JSON format with quotes around "Alex" and keys.

3. Final Answer:

   {"playerName":"Alex","level":5} -> Option D

4. Quick Check:

   JsonUtility outputs valid JSON string [OK]

Hint: JsonUtility outputs JSON with quotes around strings [OK]

Common Mistakes:

• Missing quotes around string values
• Using invalid JSON syntax
• Thinking JsonUtility needs MonoBehaviour object

4. Identify the error in this Unity C# code snippet:

using UnityEngine;

public class Player {
    public int score;
}

public class Game : MonoBehaviour {
    void Start() {
        Player player = new Player();
        string json = JsonUtility.ToJson(player);
        Debug.Log(json);
    }
}

medium

A. No error; code will output {"score":0}

B. Player class must inherit from MonoBehaviour to serialize

C. JsonUtility.ToJson requires static method call

D. score variable must be private to serialize

Solution

1. Step 1: Check if Player class can be serialized

   JsonUtility can serialize plain classes with public fields, no need to inherit MonoBehaviour.

2. Step 2: Check output of JsonUtility.ToJson

   Player's score defaults to 0, so JSON string will be {"score":0}.

3. Final Answer:

   No error; code will output {"score":0} -> Option A

4. Quick Check:

   Plain class with public fields serializes fine [OK]

Hint: Public fields in plain classes serialize without MonoBehaviour [OK]

Common Mistakes:

• Thinking class must inherit MonoBehaviour to serialize
• Assuming private fields serialize by default
• Believing JsonUtility requires static context

5. You want to save player settings including volume (float), username (string), and isFullScreen (bool) using Unity's JsonUtility. Which class definition correctly supports serialization of these variables?

hard

A. public class Settings { private float volume; private string username; private bool isFullScreen; }

B. public class Settings { [SerializeField] private float volume; [SerializeField] private string username; [SerializeField] private bool isFullScreen; }

C. public class Settings { protected float volume; protected string username; protected bool isFullScreen; }

D. public class Settings { public float volume { get; set; } public string username { get; set; } public bool isFullScreen { get; set; } }

Solution

1. Step 1: Understand JsonUtility serialization rules

   JsonUtility serializes public fields or private fields marked with [SerializeField] attribute.

2. Step 2: Evaluate each class definition

   public class Settings { protected float volume; protected string username; protected bool isFullScreen; } uses protected fields, which do not serialize. public class Settings { private float volume; private string username; private bool isFullScreen; } uses private fields without [SerializeField], so no serialization. public class Settings { [SerializeField] private float volume; [SerializeField] private string username; [SerializeField] private bool isFullScreen; } uses private fields with [SerializeField], which works. public class Settings { public float volume { get; set; } public string username { get; set; } public bool isFullScreen { get; set; } } uses properties, which JsonUtility does not serialize.

3. Step 3: Choose best practice

   Using private fields with [SerializeField] is recommended for encapsulation and serialization.

4. Final Answer:

   public class Settings { [SerializeField] private float volume; [SerializeField] private string username; [SerializeField] private bool isFullScreen; } -> Option B

5. Quick Check:

   Private fields + [SerializeField] serialize correctly [OK]

Hint: Use [SerializeField] for private variables to serialize [OK]

Common Mistakes:

• Assuming private fields serialize without attribute
• Using properties instead of fields for serialization
• Ignoring encapsulation best practices