Adding unknown components to entities

Unity Engine
,
1

Is that possible in any way? Something like:

IComponentData unknownComponent = GetUnknownComponent();
ecb.AddComponent(entity, unknownComponent);

If not, is there any alternative?

2

I do not think it is possible.
What is your use case? Why you need something like that?

3

I have a level which I create in the editor and save in a file, and in that level there are ā€œunitsā€ and each unit will have unknown ā€œextraā€ components or modifications to existing components (existing on the unit prefab). For now there are about 7 possible extra components but I will probably add moreā€¦ currently manually figuring out the concrete type using ifs and adding that insteadā€¦

4

Why not just generate authoring versions of your components and add them to those units then let conversion add them?

5

The level creation in the editor is just unit ā€œdummiesā€. Iā€™m taking those dummies and getting the necessary data, storing it in file, so I could later create the real units using that data. I am linking an enum UnitType stored in the file to the appropriate prefab after conversion. So I would instantiate that prefab and add any extra IComponentDatas to the instantiated entity.

6

I see. What you could also do is create a dictionary of EntityArchetype for each of your unit type. You then lookup that dictionary for the archetype every time you create a unit. This, however, will not included unique data for each component. It just allows you to create entities without knowing the actual components that it needs.

7

I use this method in my skill/ability system and proposed it to some in the forum which have the same issue.

It breaks abit the component are only data principle of DOTS but Iā€™m fine with it.

You can create an interface that require the implementation of a Convert method which take the entity, and entity manager as parameter.

Make your IComponentData implement that interface and call it in your couversion system.
Basically each component registers itself and htere is no issue bacause each know what they are.

2 Likes
8

Interesting, that does workā€¦ Thank you. I did not think of letting the components add themselves to the entityā€¦ however all the methods implemented of the custom interface in the components look exactly the same ( ecb.AddComponent(entity, this) ) I wonder if there is a reason we canā€™t just directly add IComponentData?

9

This is so that your components will remain as value types. Casting a struct to IComponentData will box it into a reference type. Thatā€™s just how C# works.

1 Like
10

I seeā€¦ makes sense, thank you.

11

Here you go:

using System.Reflection;
using Unity.Entities;
using UnityEngine.Assertions;

public static class ComponentDataUtility
{
    private static MethodInfo addComponentData;

    static ComponentDataUtility()
    {
        addComponentData = typeof(ComponentDataUtility).GetMethod("AddComponentData", BindingFlags.Public | BindingFlags.Static);
    }

    public static void AddComponentData<T>(EntityManager entityManager, Entity entity, T data = default) where T : struct, IComponentData
    {
        entityManager.AddComponentData(entity, data);
    }

    /// <summary>
    /// Circumvents the necessity to have a known IComponent Type at compile time.
    /// </summary>
    public static void AddComponentDataWithReflection(EntityManager entityManager, Entity entity, object data)
    {
        Assert.IsNotNull(data);
        MethodInfo function = addComponentData.MakeGenericMethod(data.GetType());
        function.Invoke(null, new object[] { entityManager, entity, data });
    }
}
2 Likes
12

I appreciate it, I had a feeling there was a way through reflectionā€¦ For what itā€™s worth, your solution got me interested and I found another solution that also worked, using dynamic-type objects:

public static void AddComponent<T>(Entity entity, EntityCommandBuffer ecb, T data) where T : struct, IComponentData
{
    ecb.AddComponent(entity, data);
}

dynamic d = myComponentData;
AddComponent(unitToAddTo, ecb, d);

https://stackoverflow.com/questions/232535/how-do-i-use-reflection-to-call-a-generic-method

Either way it seems it is a bad idea performance-wise to store components as IComponentData in the first place but for now I have no other choice so this is a good solution. Thank you

1 Like
13

Iā€™ll try the dynamic type solution for my porject thanks, it would avoid boilerplate code that make the code uggly :slight_smile:

14

Apparently you donā€™t even have to make a different method for itā€¦ just do ecb.AddComponent(unitToAddTo, (dynamic)data);

2 Likes
15

Thanks Iā€™ll try it and try to get some perf mesurement when Iā€™ll get the time.

1 Like
16

I did a quick test and it seems using dynamic is indeed faster. The average time for executing the dynamic version was 0.000661s, while the reflection version was 0.000931s. In absolute terms not a huge difference, but still :slight_smile:

EDIT: One caveat though, the dynamic option doesnā€™t seem to work with every component type. When I put in a Unity.Entities.WorldTime, I get the following exception: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: The type ā€˜System.ValueTypeā€™ must be a non-nullable value type in order to use it as parameter ā€˜Tā€™ in the generic type or method
Its probably because there is another struct inside the component type?

17

It seem dynamic is not able to cross assemblies :

WorldTime is in Entities but TimeData is in Core.

After re reading, itā€™s more likely the issue is the fact that the WorldTime is internal to Entities wich is a diferrent assembly than the one you are using the dynamic in.

1 Like
18

I think another way is to just auto-generate glue code for every marked attribute of the IComponent struct, thus you can assign values before attaching them to the entity component.