Helpful extension methods for GetSingleton and GetSingletonEntity

I noticed that GetSingleton and GetSingletonEntity both throw an InvalidOperationException if the entity count is != 1. Figured I'd share so others may benefit, or maybe get Unity to structure the 2 methods more like my extension method.

(code decompiled from Entities.dll)

Code (CSharp):

1. if (GetIndexInEntityQuery(TypeManager.GetTypeIndex<T>()) != 1)
2. {
3.     throw new InvalidOperationException($"GetSingleton<{typeof(T)}>() requires that {typeof(T)} is the only component type in its archetype.");
4. }
5. int entityCount = CalculateEntityCount();
6. if (entityCount != 1)
7. {
8.     throw new InvalidOperationException($"GetSingleton<{typeof(T)}>() requires that exactly one {typeof(T)} exists but there are {entityCount}.");
9. }

Since it is expected that sometimes a singleton entity might not always be exactly 1, such as when you restart a scene, throwing in this case is bad. I wanted a good way to get the data without potentially crashing my game, I'd rather work in a broken state than crash. You could do EntityQuery.CalculateEntityCount(), but Unity is already doing that, so I see no reason to do it twice. So I wrote these 2 methods.

They take out variables and return true/false so you can just check this really quick in an if.

Code (CSharp):

1. namespace AveaUtils
2. {
3.     public static class EntityUtils
4.     {
5.         public static bool TryGetSingleton<T>(this EntityQuery query, out T singletonComponent) where T : struct, IComponentData
6.         {
7.             try
8.             {
9.                 singletonComponent = query.GetSingleton<T>();
10.                 return true;
11.             }
12.             catch (InvalidOperationException)
13.             {
14.                 singletonComponent = default;
15.                 return false;
16.             }
17.         }
18.  
19.         public static bool TryGetSingletonEntity(this EntityQuery query, out Entity entity)
20.         {
21.             try
22.             {
23.                 entity = query.GetSingletonEntity();
24.                 return true;
25.             }
26.             catch (InvalidOperationException)
27.             {
28.                 entity = Entity.Null;
29.                 return false;
30.             }
31.         }
32.     }
33. }

Here's and example of how you may use them.

Code (CSharp):

1. CameraSettingsComponent cameraSettingsComponent;
2. if(!cameraQuery.TryGetSingleton<CameraSettingsComponent>(out cameraSettingsComponent))
3.     return;

 

Seems like this made it into ECS 17?