How do you use a Singleton?

7min
A Singleton is a design pattern that ensures there is only one instance of a particular class within a program.
The Singleton pattern provides a single global instance of a class, making it easily accessible from other scripts that need it, such as managing logic, audio, UI, and centralized resources within the world.
In ZEPETOScript, you can implement a Singleton in the following way:
TypeScript
private static _instance: ClassName = null;

public static get Instance(): ClassName {
	if (this._instance == null) {
		this._instance = GameObject.FindObjectOfType<ClassName>();
	}
	return this._instance;
}
private static _instance: ClassName = null;

public static get Instance(): ClassName {
	if (this._instance == null) {
		this._instance = GameObject.FindObjectOfType<ClassName>();
	}
	return this._instance;
}
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👍 Tips
If there is already a GameObject with a Singleton script attached in the Scene, you can use this format.
If there isn't one, add code to create the GameObject.
Example: new GameObject("ObjectName").AddComponent<ClassName>();
Let's implement a Singleton for managing UI in an example:
1) Add UI > Text and Button to the Scene.
Set up the logic to increase the score when the "IncreaseScore" button is pressed
Set up the logic to decrease the score when the "DecreaseScore" button is pressed
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2) Create a script called "ScoreManager," where the Singleton will be applied.
The ScoreManager script will be responsible for increasing/decreasing the score and updating the Text when called from other scripts.
TypeScript
import { ZepetoScriptBehaviour } from 'ZEPETO.Script';
import { GameObject } from 'UnityEngine';
import { Text } from 'UnityEngine.UI';
 
export default class ScoreManager extends ZepetoScriptBehaviour {
 
    // Singleton declaration
    private static _instance: ScoreManager = null;
 
    public static get Instance(): ScoreManager {
        if (this._instance == null) {
            this._instance = GameObject.FindObjectOfType<ScoreManager>();
        }
 
        return this._instance;
    }
 
    // Variable declaration
    public scoreText: Text;
    private _currentScore : number;
 
    Start() {   
        // Set initial score to 0 for testing
        this._currentScore = 0;
    }
 
    // Other scripts can call IncreaseScore
    public IncreaseScore(amount: number) {
        this._currentScore += amount;
        this.scoreText.text = `Score : ${this._currentScore}`;
    }
 
    // Other scripts can call DecreaseScore
    public DecreaseScore(amount: number) {
        this._currentScore -= amount;
        this.scoreText.text = `Score : ${this._currentScore}`;
    }
 
}

import { ZepetoScriptBehaviour } from 'ZEPETO.Script';
import { GameObject } from 'UnityEngine';
import { Text } from 'UnityEngine.UI';
 
export default class ScoreManager extends ZepetoScriptBehaviour {
 
    // Singleton declaration
    private static _instance: ScoreManager = null;
 
    public static get Instance(): ScoreManager {
        if (this._instance == null) {
            this._instance = GameObject.FindObjectOfType<ScoreManager>();
        }
 
        return this._instance;
    }
 
    // Variable declaration
    public scoreText: Text;
    private _currentScore : number;
 
    Start() {   
        // Set initial score to 0 for testing
        this._currentScore = 0;
    }
 
    // Other scripts can call IncreaseScore
    public IncreaseScore(amount: number) {
        this._currentScore += amount;
        this.scoreText.text = `Score : ${this._currentScore}`;
    }
 
    // Other scripts can call DecreaseScore
    public DecreaseScore(amount: number) {
        this._currentScore -= amount;
        this.scoreText.text = `Score : ${this._currentScore}`;
    }
 
}
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Script Description
private static _instance: This is a private static variable within the class, initially set to null.
public static get Instance: This static property provides a way for external code to access the unique instance of this class.
Check if (this.\_instance == null).  If it’s null, use GameObject.FindObjectOfType<>() to find and return a component of type ClassName, and assign it to the static variable.
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3) After writing the script, return to the Inspector and connect the Text component.
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4) Next, create a script called "ScoreLogicSample" to demonstrate how to call the Singleton. Ensure that ScoreManager and ScoreLogicSample are in the same directory.
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Write code like this:
TypeScript
import { ZepetoScriptBehaviour } from 'ZEPETO.Script';
import { GameObject } from 'UnityEngine';
import { Text, Button } from 'UnityEngine.UI';
// Import Singleton script
import ScoreManager from './ScoreManager';
 
export default class ScoreLogicSample extends ZepetoScriptBehaviour {
 
    public increaseScoreButton: Button;
    public decreaseScoreButton: Button;
 
    // Declare variable of type ScoreManager
    private ScoreManager : ScoreManager;
 
    Start() {   
 
        // Assign ScoreManager to the variable
        this.ScoreManager = GameObject.FindObjectOfType<ScoreManager>();
 
        this.increaseScoreButton.onClick.AddListener(()=> {
            // Call the function declared in Singleton
            this.ScoreManager.IncreaseScore(10);
        });
 
        this.decreaseScoreButton.onClick.AddListener(()=> {
            // Call the function declared in Singleton
            this.ScoreManager.DecreaseScore(10);
        });
    }
}
import { ZepetoScriptBehaviour } from 'ZEPETO.Script';
import { GameObject } from 'UnityEngine';
import { Text, Button } from 'UnityEngine.UI';
// Import Singleton script
import ScoreManager from './ScoreManager';
 
export default class ScoreLogicSample extends ZepetoScriptBehaviour {
 
    public increaseScoreButton: Button;
    public decreaseScoreButton: Button;
 
    // Declare variable of type ScoreManager
    private ScoreManager : ScoreManager;
 
    Start() {   
 
        // Assign ScoreManager to the variable
        this.ScoreManager = GameObject.FindObjectOfType<ScoreManager>();
 
        this.increaseScoreButton.onClick.AddListener(()=> {
            // Call the function declared in Singleton
            this.ScoreManager.IncreaseScore(10);
        });
 
        this.decreaseScoreButton.onClick.AddListener(()=> {
            // Call the function declared in Singleton
            this.ScoreManager.DecreaseScore(10);
        });
    }
}
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It's important to specify the path correctly when getting the Singleton script.
You can adapt the part where ScoreManager is called in your own script as needed.
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5) Press the [▶︎(play)] button to test.
You should observe the functions in ScoreManager being called when you click the buttons in ScoreLogicSample, making it work as expected.
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Updated 10 Oct 2024
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