SystemBase：支持主线程或多线程执行筛选实体任务。
主要介绍是内部成员：Entities的各种筛选方法，其内部成员还有EntityManager

ForEach方法筛选，传递一个有参委托函数进去，参数ref xxx组件类（可填多个）代表筛选条件。

WithAll：&& 形式筛选组件
WithAny： || 形式筛选组件
WithNone： 筛选出不带某组件的
WithChangeFilter：监听组件数据变化时触发筛选
WithSharedComponentFilter：筛选共享组件（指定特定数据）
WithStoreEntityQueryInField(ref EntityQuery对象)：存储筛选结果
WithEntityQueryOptions(EntityQueryOptions)：
        EntityQueryOptions.FilterWriteGroup：筛选带[WriteGroup(typeof(xxx))特性的组件
        EntityQueryOptions.IncludeDisabled：具有Disabled（已禁用）组件的实体
        EntityQueryOptions.IncludePrefab：具有Prefab组件的实体
WithoutBurst：不使用Burst编译
WithBurst：使用Burst编译

Run：主线程（单线程执行）
Schedule：多线程并发
ScheduleParallel：多线程并行

using System.Collections;
using System.Collections.Generic;
using Unity.Collections;
using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;
/// <summary>
/// 可操作主线程或多线程； ComponentSystem单线程 JobComponentSystem多线程
/// </summary>
public class MySystemBase : SystemBase
{
    EntityQuery query;
    //以下方法从上到下按顺序执行
    protected override void OnCreate()
    {
        Debug.Log("OnCreate");
    }

    protected override void OnStartRunning()
    {
        Debug.Log("OnStartRunning");
    }

    protected override void OnUpdate()
    {
        Debug.Log("OnUpdate");

        //使用内部成员Entities遍历所有实体筛选出Translation组件的实体进行修改
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).Run();


        //使用WithAll增加筛选条件，必须带有PrintTestComponentData组件的
        //使用Run()代表是主线程执行
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithAll<PrintTestComponentData>().Run();

        //WithAny 只要带任意一个即可满足筛选
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithAny<PrintTestComponentData>().Run();

        //WithNone 不包含xxx的
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithNone<PrintTestComponentData>().Run();

        //WithChangeFilter 监听组件值变化时才触发方法体，参数必须带上ref PrintTestComponentData  否则会报错
        Entities.ForEach((ref Translation trans, ref PrintTestComponentData data) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithChangeFilter<PrintTestComponentData>().Run();

        //WithSharedComponentFilter 筛选共享组件 特定值为2的
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithSharedComponentFilter(new MyShareComponentData() { data = 2 }).Run();

        //存储筛选结果        
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithStoreEntityQueryInField(ref query).Run();

        NativeArray<Entity> array = query.ToEntityArray(Unity.Collections.Allocator.TempJob);
        foreach (var v in array)
        {
            //do something
        }

        //过滤出带[WriteGroup]特性的组件实体  [WriteGroup(typeof(PrintTestComponentData))] 查询会根据查询中指定的组件的WriteGroupAttribute属性筛选所选实体
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithEntityQueryOptions(EntityQueryOptions.FilterWriteGroup).Run();

        //过滤出带[DisableAutoCreation]特性的组件实体  该查询不会隐式的排除具有Disabled（已禁用）组件的实体
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithEntityQueryOptions(EntityQueryOptions.IncludeDisabled).Run();

        //过滤出预制体实体  [DisableAutoCreation]  该查询不会隐式的排除具有Prefab组件的实体
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithEntityQueryOptions(EntityQueryOptions.IncludePrefab).Run();

        //Schedule 多线程并发执行 ; WithoutBurst 不使用Burst编译
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithoutBurst().Schedule();

        //ScheduleParallel 配合Job 多线程并行执行 WithBurst 使用Burst编译
        Entities.ForEach((ref Translation trans) =>
        {
            trans.Value = new Unity.Mathematics.float3(0, 5, 0);
        }).WithBurst().ScheduleParallel();

        query.Dispose();
        array.Dispose();
    }

    protected override void OnStopRunning()
    {
        Debug.Log("OnStopRunning");
    }

    protected override void OnDestroy()
    {
        Debug.Log("OnDestroy");
    }
}