JSON serialization in Unity

Introduction

JSON serialization helps you turn your game data into text that can be saved or sent. It makes your data easy to store and share.

Saving player progress like scores or settings to a file.

Sending game data over the internet to a server or other players.

Loading game settings or levels from a saved file.

Debugging by printing data in a readable format.

Sharing configuration data between different parts of your game.

Syntax

Unity

using UnityEngine;

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

// To convert object to JSON string:
string jsonString = JsonUtility.ToJson(yourObject);

// To convert JSON string back to object:
PlayerData data = JsonUtility.FromJson<PlayerData>(jsonString);

The class you want to serialize must be marked with [System.Serializable].

Use JsonUtility.ToJson() to convert an object to JSON text.

Examples

This creates a player object and turns it into a JSON string.

Unity

PlayerData player = new PlayerData();
player.playerName = "Alex";
player.score = 100;
string json = JsonUtility.ToJson(player);

This takes a JSON string and turns it back into a PlayerData object.

Unity

string json = "{\"playerName\":\"Alex\",\"score\":100}";
PlayerData player = JsonUtility.FromJson<PlayerData>(json);

Sample Program

This Unity script creates a player object, converts it to JSON text, prints it, then reads the JSON back into an object and prints the data.

Unity

using UnityEngine;

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

public class JsonExample : MonoBehaviour {
    void Start() {
        PlayerData player = new PlayerData();
        player.playerName = "Alex";
        player.score = 100;

        // Serialize to JSON
        string json = JsonUtility.ToJson(player);
        Debug.Log("JSON string: " + json);

        // Deserialize back to object
        PlayerData loadedPlayer = JsonUtility.FromJson<PlayerData>(json);
        Debug.Log($"Player name: {loadedPlayer.playerName}, Score: {loadedPlayer.score}");
    }
}

Important Notes

Only public fields are serialized by default.

Properties (get/set) are not serialized by JsonUtility.

JsonUtility works well for simple data but not complex types like dictionaries.

Summary

JSON serialization converts objects to text and back.

Use JsonUtility.ToJson() and FromJson() in Unity.

Mark classes with [System.Serializable] and use public fields.

Practice

1.

What is the main purpose of JSON serialization in Unity?

easy

A. Create 3D models from code

B. Convert objects into text format and back

C. Compile scripts faster

D. Optimize game performance automatically

Solution

1. Step 1: Understand JSON serialization

   JSON serialization means turning objects into text so they can be saved or sent.

2. Step 2: Recognize Unity's use

   Unity uses JSON serialization to save object data as text and load it back.

3. Final Answer:

   Convert objects into text format and back -> Option B

4. Quick Check:

   JSON serialization = Convert objects to text and back [OK]

Hint: Think: saving objects as readable text [OK]

Common Mistakes:

• Confusing serialization with 3D modeling
• Thinking it speeds up script compilation
• Assuming it optimizes performance automatically

2.

Which of the following is the correct way to serialize an object player to JSON in Unity?

Player player = new Player();

easy

A. string json = JsonUtility.ToJson(player);

B. string json = Json.Serialize(player);

C. string json = JsonUtility.FromJson(player);

D. string json = player.ToJson();

Solution

1. Step 1: Identify Unity's serialization method

   Unity uses JsonUtility.ToJson() to convert objects to JSON text.

2. Step 2: Check method usage

   JsonUtility.ToJson(player) correctly serializes the player object.

3. Final Answer:

   string json = JsonUtility.ToJson(player); -> Option A

4. Quick Check:

   Serialize with JsonUtility.ToJson() [OK]

Hint: Use JsonUtility.ToJson() to serialize objects [OK]

Common Mistakes:

• Using FromJson() instead of ToJson()
• Calling non-existent Json.Serialize() method
• Trying to call ToJson() on the object itself

3.

Given the following code, what will be the output?

[System.Serializable]
public class Player {
    public string name = "Alex";
    public int score = 10;
}

Player player = new Player();
string json = JsonUtility.ToJson(player);
Debug.Log(json);

medium

A. {"name":"Alex","score":10}

B. {"name":"Alex"}

C. {"score":10}

D. Error: Player class not serializable

Solution

1. Step 1: Check class serialization

   The Player class is marked [System.Serializable], so it can be converted to JSON.

2. Step 2: Understand JsonUtility.ToJson output

   It converts all public fields to JSON key-value pairs, so name and score appear.

3. Final Answer:

   {"name":"Alex","score":10} -> Option A

4. Quick Check:

   Serializable class fields appear in JSON [OK]

Hint: Serializable class fields become JSON keys [OK]

Common Mistakes:

• Forgetting [System.Serializable] attribute
• Expecting private fields to appear
• Thinking only one field is serialized

4.

What is wrong with this code snippet for deserializing JSON into a Player object?

string json = "{\"name\":\"Sam\", \"score\":15}";
Player player = JsonUtility.ToJson(json);

medium

A. JSON string is not properly formatted

B. Player class must be private

C. Using ToJson() instead of FromJson() for deserialization

D. Missing semicolon after JSON string

Solution

1. Step 1: Identify method misuse

   JsonUtility.ToJson() is for serialization, not deserialization.

2. Step 2: Correct method for deserialization

   Use JsonUtility.FromJson<Player>(json) to convert JSON text back to Player object.

3. Final Answer:

   Using ToJson() instead of FromJson() for deserialization -> Option C

4. Quick Check:

   Deserialize with FromJson(), not ToJson() [OK]

Hint: Use FromJson() to convert JSON text to object [OK]

Common Mistakes:

• Mixing ToJson() and FromJson() methods
• Assuming JSON string format is wrong
• Thinking class visibility affects serialization

5.

You want to save a list of Player objects to JSON and load them back later. Which approach correctly handles this in Unity?

hard

A. Serialize the list directly with JsonUtility.ToJson(playersList)

B. Use JsonUtility.FromJson<List<Player>>(json) to deserialize

C. Serialize each Player separately and concatenate JSON strings

D. Wrap the list in a serializable container class and serialize that

Solution

1. Step 1: Understand Unity's JsonUtility limitation

   JsonUtility cannot serialize lists directly; it needs a wrapper class.

2. Step 2: Use a container class

   Create a [System.Serializable] class with a public List<Player> field and serialize that.

3. Final Answer:

   Wrap the list in a serializable container class and serialize that -> Option D

4. Quick Check:

   Wrap lists in container class for JSON serialization [OK]

Hint: Wrap lists in a class before serializing [OK]

Common Mistakes:

• Trying to serialize lists directly
• Concatenating JSON strings manually
• Using FromJson with generic List type