Get entity count of a ForEach before going through the ForEach

So this is my old deprecated code:

Code (CSharp):

1.     public unsafe struct CropTileQuerry {
2.         public CropTile* tile;
3.         public Transform transform;
4.     }
5.     public unsafe void Serialize(BinaryWriter bw) {
6.         ComponentGroupArray<CropTileQuerry> componentGroupArray = GetEntities<CropTileQuerry>();
7.         bw.Write(componentGroupArray.Length);
8.         foreach (CropTileQuerry q in componentGroupArray) {
9.             Vector3 position = q.transform.position;
10.             bw.Write(position.x);
11.             bw.Write(position.y);
12.             bw.Write(position.z);
13.         }
14.     }

I would save the length before saving the positions, but I can't really do that with ForEach as far as I am aware. Right now I am setting the BinaryWriter

BaseStream

Position

back after counting and writing the positions to write at the beginning the total amount of crop tiles, but I am not sure that even works. Is there any ECS way to count the total amount of entities before iterating them?

 

Using an EntityQuery you can. Assuming this code is running inside a ComponentSystemBase:

Code (CSharp):

1. EntityQuery query = GetEntityQuery(
2.             ComponentType.ReadOnly<CropTileQuerry>()
3. );
4.  
5. int count = query.CalculateLength();

Then you can get out a NativeArray of the Entities:

Code (CSharp):

1. var entities = query.ToEntityArray(Allocator.Temp);
2. ...
3.  
4. entities.Dispose();

 

Nice, also, ToEntityArray is faster than ForEach?

 

I'm not aware of a way to foreach on an EntityQuery unless you're using it to Schedule an IJobForEach, but I haven't used non-job ComponentSystems much so I could be missing something!

 

Code (CSharp):

1. void OnUpdate() {
2.     var count = myEntityQuery.CalculateLength();
3.     Entities
4.         .With(myEntityQuery)
5.         .ForEach((...) => {
6.             ...
7.         });
8. }

[]'s