AI doesn't have any trigger to see a player and follow it

So I have a script that he patrols then when he spots the player he follows the player everything works BUT he cant spot the player I have to manually click a button can someone help im very new to scripting.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.AI;
5. public class Enemy : MonoBehaviour
6. {
7.      //Variables
8.      public Transform[] patrolPoints;
9.      private int destPoint = 0;
10.      private NavMeshAgent agent;
11.      public bool playerInRadius;
12.      public int speed;
13.      public GameObject player;
14.      public EnemyTypes eCurState = EnemyTypes.Patrol;
15.      void Start ()
16.      {
17.          //Sets NavMeshAgent
18.          agent = GetComponent<NavMeshAgent> ();
19.      }
20.      void GoToNextPoint ()
21.      {
22.          //If no patrol points are set
23.          if (patrolPoints.Length == 0)
24.          {
25.              return;
26.          }
27.          //Sets the destination to all the different positions stated in the inspector
28.          agent.destination = patrolPoints [destPoint].position;
29.          destPoint = (destPoint + 1) % patrolPoints.Length;
30.      }
31.      void FixedUpdate ()
32.      {
33.          //If the player is in the detection radius
34.          if (playerInRadius)
35.          {
36.              //Chase
37.              eCurState = EnemyTypes.Chase;
38.          }
39.          //If the player is not
40.          if (!playerInRadius)
41.          {
42.              //Go back to patrolling
43.              eCurState = EnemyTypes.Patrol;
44.          }
45.          switch (eCurState)
46.          {
47.          case EnemyTypes.Chase:
48.              HandleChase ();
49.              break;
50.          case EnemyTypes.Patrol:
51.              HandlePatrol ();
52.              break;
53.          }
54.      }
55.      public enum EnemyTypes
56.      {
57.          Patrol,
58.          Chase
59.      }
60.      void HandlePatrol ()
61.      {
62.          if (!agent.pathPending && agent.remainingDistance < 0.5f)
63.          {
64.              GoToNextPoint ();
65.          }
66.      }
67.      //Handles chase
68.      void HandleChase ()
69.      {
70.          agent.destination = player.transform.position;
71.      }
72. }
73.  

 

That's because you haven't set the way the enemy spots the player. For example you should check the distance between the player and the enemy and if it is small enough to spot the player, playerInRadius should be changed to true and if the player is too far then to false. Then it will work.