How to detect if the player is grounded

This is my script, it's look not so bad but when I enter playmode and check the my player in the entity debugger, the grounded field in the PlayerMovementData component is not check. Can anyone tell me what's wrong with my script. Thanks in advance!
PlayerMovementData:

Code (CSharp):

1. using Unity.Entities;
2. using UnityEngine;
3.  
4. [GenerateAuthoringComponent]
5. public struct PlayerMovementData : IComponentData
6. {
7.     [HideInInspector]
8.     public bool grounded;
9. }

PlayerGroundedSystem:

Code (CSharp):

1. private struct PlayerGroundedJob : ICollisionEventsJob
2.     {    
3.         [ReadOnly] public ComponentDataFromEntity<GroundTag> ground;
4.  
5.         public ComponentDataFromEntity<PlayerMovementData> movementData;
6.         public void Execute(CollisionEvent collisionEvent)
7.         {
8.             Entity entityA = collisionEvent.Entities.EntityA;
9.             Entity entityB = collisionEvent.Entities.EntityB;
10.  
11.             if (ground.HasComponent(entityA) && movementData.HasComponent(entityB))
12.             {
13.                 PlayerMovementData move = movementData[entityB];
14.                 move.grounded = true;
15.                 movementData[entityB] = move;
16.             }
17.             else if (ground.HasComponent(entityB) && movementData.HasComponent(entityA))
18.             {
19.                 PlayerMovementData move = movementData[entityA];
20.                 move.grounded = true;
21.                 movementData[entityA] = move;
22.             }
23. }