unity3d Singletons in Unity Singleton Pattern utilizing Unitys Entity-Component system
Example
The core idea is to use GameObjects to represent singletons, which has multiple advantages:
- Keeps complexity to a minimum but supports concepts like dependency injection
- Singletons have a normal Unity lifecycle as part of the Entity-Component system
- Singletons can be lazy loaded and cached locally where regulary needed (e.g. in update loops)
- No static fields needed
- No need to modify existing MonoBehaviours / Components to use them as Singletons
- Easy to reset (just destroy the Singletons GameObject), will be lazy loaded again on next usage
- Easy to inject mocks (just initialize it with the mock before using it)
- Inspection and configuration using normal Unity editor and can happen already on editor time ( Screenshot of a Singleton accessible in the Unity editor )
Test.cs (which uses the example singleton):
using UnityEngine;
using UnityEngine.Assertions;
public class Test : MonoBehaviour {
void Start() {
ExampleSingleton singleton = ExampleSingleton.instance;
Assert.IsNotNull(singleton); // automatic initialization on first usage
Assert.AreEqual("abc", singleton.myVar1);
singleton.myVar1 = "123";
// multiple calls to instance() return the same object:
Assert.AreEqual(singleton, ExampleSingleton.instance);
Assert.AreEqual("123", ExampleSingleton.instance.myVar1);
}
}
ExampleSingleton.cs (which contains an example and the actual Singleton class):
using UnityEngine;
using UnityEngine.Assertions;
public class ExampleSingleton : MonoBehaviour {
public static ExampleSingleton instance { get { return Singleton.get<ExampleSingleton>(); } }
public string myVar1 = "abc";
public void Start() { Assert.AreEqual(this, instance, "Singleton more than once in scene"); }
}
/// <summary> Helper that turns any MonBehaviour or other Component into a Singleton </summary>
public static class Singleton {
public static T get<T>() where T : Component {
return GetOrAddGo("Singletons").GetOrAddChild("" + typeof(T)).GetOrAddComponent<T>();
}
private static GameObject GetOrAddGo(string goName) {
var go = GameObject.Find(goName);
if (go == null) { return new GameObject(goName); }
return go;
}
}
public static class GameObjectExtensionMethods {
public static GameObject GetOrAddChild(this GameObject parentGo, string childName) {
var childGo = parentGo.transform.FindChild(childName);
if (childGo != null) { return childGo.gameObject; } // child found, return it
var newChild = new GameObject(childName); // no child found, create it
newChild.transform.SetParent(parentGo.transform, false); // add it to parent
return newChild;
}
public static T GetOrAddComponent<T>(this GameObject parentGo) where T : Component {
var comp = parentGo.GetComponent<T>();
if (comp == null) { return parentGo.AddComponent<T>(); }
return comp;
}
}
The two extension methods for GameObject are helpful in other situations as well, if you don't need them move them inside the Singleton class and make them private.
