Trying to build system without hard coupling

Question

I'm building a simple strategy game and stumble on multiple problems with communication between components. So i have "Unit" object, "Camera" object and UI. The idea is that when you click on Unit, camera moves to its position and UI displays some text. My approach:

 public class Unit : MB
 {
     public event Action OnSelected;
     public void Select()
     {
         OnSelected?.Invoke(this);
     }
 }

Unit invokes delegate and passes self, so camera and UI can use its public fields

 public class Camera : MB
 {
     private void OnEnable()
     {
         foreach (Unit unit in FindObjectsOfType<Unit>())
             unit.OnSelected += MoveTo;
     }

     public void MoveTo(Unit unit) { // some code }
 }

First problem comes from Camera. In order to subscribe i must search entire scene for all Units and then subscribe. But i can't subscribe for new ones. In order to battle this i must implement some sort of spawner mechanics. But my code gets convoluted quickly and it still uses FindObjectsOfType<>. Something like this:

 private void SubscribeToAllSpawners()
     foreach (Spawner spawner in FindObjectsOfType<Spawner>())
         spawner.OnSpawned += SubscribeToUnit;

 private void SubscriptToUnit(Unit unit)
     unit.OnSelected += MoveTo;

And i need two more methods to unsubscribe. Feels like too much for problem like this, and i need to write almost exactly the same code for UI component. Is there some sort of pattern that i don't know of?

Second problem is that i want to reuse "MoveTo" camera method and pass Vector3 as its parameter. I can subscribe using lambda expression:

 unit.OnSelect += (unit) => MoveTo(unit.transform.position);

but a don't know how to unsubscribe. Please help

Answer 1

Regarding the second problem, you need a reference to the method you want to remove from the event. You're creating a new method using the lambda expression that wraps around your MoveTo method. It either needs to be stored in a variable for later use or you should just make an ordinary method that will contain a call to MoveTo. I would make a method called OnUnitSelected or something like that.

Regarding the first problem, I can offer two solutions.

Simple solution

Make a static version of OnSelected event for the units. That could be used to catch the moment when any of the active units are selected.
Reference: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/static

 public class Unit : MonoBehaviour
 {
     public static event Action<Unit> AnyInstanceSelected;
 
     public void Select()
     {
         AnyInstanceSelected?.Invoke(this);
     }
 }

 public class CameraController : MonoBehaviour
 {
     private void OnEnable()
     {
         Unit.AnyInstanceSelected += OnUnitSelected;
     }
 
     private void OnDisable()
     {
         Unit.AnyInstanceSelected -= OnUnitSelected;
     }
 
     private void OnUnitSelected(Unit unit)
     {
         // ...
     }
 }

Complex solution

Make a container that units will add themselves to upon instantiation. This container then could be passed around to whoever needs it.
Reference: https://docs.unity3d.com/Manual/class-ScriptableObject.html

 [CreateAssetMenu(
     fileName = "New Unit Container",
     menuName = "Unit Container")]
 public class UnitContainer : ScriptableObject
 {
     public event Action<Unit> UnitAdded;
     public event Action<Unit> UnitRemoved;
 
     public ReadOnlyCollection<Unit> Units => units.AsReadOnly();
     private List<Unit> units = new List<Unit>();
 
     public void Add(Unit unit)
     {
         units.Add(unit);
         UnitAdded?.Invoke(unit);
     }
 
     public void Remove(Unit unit)
     {
         units.Remove(unit);
         UnitRemoved?.Invoke(unit);
     }
 }

 public class Unit : MonoBehaviour
 {
     public event Action<Unit> Selected;
     public UnitContainer container;
 
     public void Select()
     {
         Selected?.Invoke(this);
     }
 
     private void OnEnable()
     {
         if (container != null)
         {
             container.Add(this);
         }
     }
 
     private void OnDisable()
     {
         if (container != null)
         {
             container.Remove(this);
         }
     }
 }

 public class CameraController : MonoBehaviour
 {
     [SerializeField]
     private UnitContainer unitContainer = null;
 
     private void OnEnable()
     {
         foreach (Unit unit in unitContainer.Units)
         {
             unit.Selected += OnUnitSelected;
         }
         unitContainer.UnitAdded += OnUnitAdded;
         unitContainer.UnitRemoved += OnUnitRemoved;
     }
 
     private void OnDisable()
     {
         foreach (Unit unit in unitContainer.Units)
         {
             unit.Selected -= OnUnitSelected;
         }
         unitContainer.UnitAdded -= OnUnitAdded;
         unitContainer.UnitRemoved -= OnUnitRemoved;
     }
 
     private void OnUnitSelected(Unit unit)
     {
         // ...
     }
 
     private void OnUnitAdded(Unit unit)
     {
         unit.Selected += OnUnitSelected;
     }
 
     private void OnUnitRemoved(Unit unit)
     {
         unit.Selected -= OnUnitSelected;
     }
 }

Answer 2

Answer by kirbygc00 · Apr 12, 2020 at 12:58 AM

answer to problem 2 is: unit.OnSelect -= yourFunc;.

You may have to assign your lambda to some function i haven't tred unassigning a lambda.

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Trying to build system without hard coupling

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Simple solution

Complex solution

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