Inside structs cannot access instance members of 'this'

Unity Engine
,
1

Hi

I updated my project to ECS 0.50 and now I get error messages.

The error message is as follows

I don’t think my code is accessing the members of this, but I don’t understand why I am getting this error message.

This did not occur in ECS 0.17.

Can anyone help me understand this error?

TestComponent.cs
```
using Unity.Entities;

[System.Serializable]
public struct TestComponent : IComponentData
{
    public int id;
}
```

Test2Component.cs
```
using System;
using Unity.Entities;

[System.Serializable]
public struct Test2Component : IComponentData
{
    public string id;
}
```

CallbackEvent.cs
```
using System;
using Unity.Entities;

[System.Serializable]
public struct CallbackEvent : IComponentData
{
    public int actionId;
}
```

CallbackSystem.cs
```
using System;
using System.Collections.Generic;
using Unity.Entities;

public partial class CallbackSystem : SystemBase
{
    EntityCommandBufferSystem _entityCommandBufferSystem;
    Dictionary<int, Action<EntityCommandBuffer>> _callbacks;
    int _actionIdSequential;

    public CallbackEvent CreateCallback(Action<EntityCommandBuffer> action)
    {
        var actionId = _actionIdSequential++;
        _callbacks[actionId] = action;
        return new CallbackEvent {
            actionId = actionId,
        };
    }

    protected override void OnCreate()
    {
        _entityCommandBufferSystem = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
        _callbacks = new Dictionary<int, Action<EntityCommandBuffer>>();
    }

    protected override void OnUpdate()
    {
      
    }
}
```

TestSystem.cs
```
using Unity.Entities;

public partial class TestSystem : SystemBase
{
    CallbackSystem _callbackSystem;
  
    protected override void OnUpdate()
    {
        Entities
            .WithoutBurst()
            .WithAll<TestComponent>()
            .ForEach((
                Entity entity,
                int entityInQueryIndex
            ) => {
                var str = "str";

                var onArrived = _callbackSystem.CreateCallback(buffer => {
                    buffer.AddComponent(entity, new Test2Component {
                        id = str, // ng
                        // id = "str", // ok
                    });
                });
            }).Run();
    }
}
```
2

I don‘t see it right away, but I noticed that TestComponent is a class, not a struct.

1 Like
3

Thank you for your reply!

Ah!!! You are right, I had overlooked that.

I tried to set TestComponent to struct, but unfortunately the error content did not improve.

4

You have few issue here.

First, you should not pass any managed tpye to your job. I. E Dictionary or classes.

Second, you should not have any string operations in a jobs.

Third, passing variables to job, which are outside of OnUpdate scope, require local variable and THIS.

For example in line 76, should become
var _callbackSystem = this. _callbackSystem;

5

Thank you kindly! It helps!!!

First, you should not pass any managed tpye to your job. i. E Dictionary or classes.
Which code is applicable here?
Is it the use of _callbacks(Dictionary) in the CreateCallback function?

Second, you should not have any string operations in a job.
Noted. Thank you.

Third, passing variables to a job, which are outside of the OnUpdate scope, requires local variables and THIS.
So this is how you would do it.

var _callbackSystem = this._callbackSystem;
Entities
.WithoutBurst()
.WithAll<TestComponent>()
.ForEach((
Entity entity,
int entityInQueryIndex
) => {
var str = "str";
var onArrived = _callbackSystem.CreateCallback(buffer => {
buffer.AddComponent(entity, new Test2Component {
id = "str",
});
});
}).Run();
6

You still need to remove the string, they are not allowed in struct IComponentData, see this for allowed types:

https://docs.unity3d.com/Packages/com.unity.entities@0.50/manual/ecs_components.html

7

I see. Thank you very much.

8

Hi, I have the same issue, at Entity 0.50.1-preview.2 and Unity 2020.3.33.f1.

And this is the minimum example.

Entities
  .ForEach((
    Entity entity,
    int entityInQueryIndex
  ) => {
    var str = "str";
    var action = new Action(() => {
      Debug.Log(str);
    });
  }).Run();

Error message is below.(at Debug.Log(str); line)

On Entity 0.17.0-preview.42, I could create lambda in Entities.ForEach.
How can I create lambda in Entities.ForEach of 0.50?

Thanks for your help.

9

@ryooo321
One way to do it would be having static functions to create them, either in the job lambda or somewhere else.

Job.WithoutBurst().WithCode(() =>
            {
                static Action CreateDelegate(string str) => () => Debug.Log(str);
                string str = "str";
                var action = CreateDelegate(str);
                action();
            }).Run();
1 Like
10

@Anthiese
Thank you, Your example has no error.

Or I have fixed by using for statement.

    var entities = query.ToEntityArrayAsync(Allocator.TempJob, out var handle);
    Dependency = JobHandle.CombineDependencies(Dependency, handle);
    for (int i = 0; i < entities.Length; i++) {
      var entity = entities[i];
      var str = "str";
      var action = new Action(() => {
        Debug.Log(str);
      });
    }
    entities.Dispose(Dependency);