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c#design-patternsunity-game-engine
agiro
agiro

Reputation: 2080

Expose a Singleton to other classes using an interface

I'm making a game in Unity C# using a Singleton GameManager and I was warned that using references of the class in other scripts like GameManager.instance.someVar makes the code fragile and difficult for later edit. So I looked for how to access a singleton with interfaces but haven't found what I was after. As I wish to code properly, I would like someone to point me to a decent source that tells me how to do so, or have him/her tell me in brief.

Upvotes: 1

Views: 1136

Answers (3)

David Guida
David Guida

Reputation: 1155

Usually I tend to create an empty GameObject, give it a proper name or a tag and attach a script component to it.

This way I can easily get a reference in any other GameObject that might need it and retrieve the script component from it.

Upvotes: 0

Stephen Byrne
Stephen Byrne

Reputation: 7485

Well there is a general solution to this, I am not sure how feasible it will be for you.

Suppose we have a true singleton:

public static class Highlander //cos, there can be only one. Sorry. couldn't resist
{
   public static void Quicken(string name)
   {
      Console.WriteLine("{0} gets their quickening on",name);
   }
}

Suppose we want to be able to pass this around in an abstract manner, using Interfaces.

public interface IImmortal
{
    void Quicken();
}

Well, you cannot implement an interface on a static class or member, so how do you pass references to this class around by interface?

Simple - create a wrapper/adapter class which implements the interface you want:

public class McLeod: IImortal
{
   public void Quicken()
   {
       Highlander.Quicken("Conor");
   }
}

public class Kurgen: IImortal
{
   public void Quicken()
   {
       Highlander.Quicken("The Kurgen");
   }
}

Now you can pass IImortal around, and the wrapping implementation(s) simply call through to the Singleton. Note how the Wrapper can supply data to the Singleton from within itself, as above, in which case it's more like an Adapter. But the concept is the same.

In the case of Unity, I don't know if this will suit, since the GameManager class likely exposes a ton of other properties and methods you would also have to wrap/adapt - it may not be worth creating wrapper interfaces for all of this, so consider perhaps that in this case you need to embrace it :)

Upvotes: 2

PhillipH
PhillipH

Reputation: 6222

Singletons, being static, dont support interfaces. Perhaps your other source might mean that you should use a Factory pattern or perhaps an Inversion of Control (IOC) method. In those cases the Factory would look like GameManagerFactory.GetGameInstance() rather than refer to the Instance static property of a GameManager.

The true limitation of Singlton programming is in the area of unit testing - because your code is bound directly to the specific class "GameManager" you could not replace it in a unit test with another "test version" of the GameManager. To support unit testing you should try to make sure that any significant classes your code depends on could be replaced by a test version of a class, without your code caring. When using Singletons this is hard (if not impossible) to do.

Upvotes: 0

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