How can I set up enemies spawning in set locations in every level in my Unity game?

Question

I'm new to Unity and I've made a game in which I can make the levels using prefabs quickly, but I found that making Enemies in prefabs isn't a good idea because they can't follow or interact with the player. What is the best way to make Enemies spawn as soon as the level generates without having to individually create every single one?

Player Code (or at least the instance variables without the methods):

public class PlayerPhys : MonoBehaviour
{
[SerializeField] private float m_JumpForce = 400f;                          
[Range(0, 1)] [SerializeField] private float m_CrouchSpeed = .36f;          
[Range(0, .3f)] [SerializeField] private float m_MovementSmoothing = .05f;
[SerializeField] private bool m_AirControl = true;                         
[SerializeField] private LayerMask m_WhatIsGround;                          
[SerializeField] private Transform m_GroundCheck;                           
[SerializeField] private Transform m_CeilingCheck;                          
[SerializeField] private Collider2D m_CrouchDisableCollider;                

const float k_GroundedRadius = .2f;
private bool m_Grounded;
const float k_CeilingRadius = .2f;
private Rigidbody2D m_Rigidbody2D;
private bool m_FacingRight = true;
private Vector3 m_Velocity = Vector3.zero;

[Header("Events")]
[Space]

public UnityEvent OnLandEvent;

[System.Serializable]
public class BoolEvent : UnityEvent<bool> { }

public BoolEvent OnCrouchEvent;
private bool m_wasCrouching = false;

private Animator m_Anim;

Transform playerGraphics;

Enemy prefab code I have so far:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class EnemyAttack : MonoBehaviour
{
    public int health = 1;

    // Update is called once per frame
    void Update()
    {
        // Destroy this if killed
        if (health <= 0)
        {
            Destroy(gameObject);
        }
    }

    // Take damage
    public void TakeDamage(int damage)
    {
        health -= damage;
    }
}

I used this Brackeys tutorial to create levels, and all I'm confused about is how I can make it so that the level creator can create enemies which can interact with the player. I wish he went over how he made prefabricated coins able to be picked up by the player

Answer 1

To get a reference to the player. I normally add to my scene an empty game-object called 'GAME_MANAGER' or similar. Attach to this a script with similar name GameManager.cs for example.

Inside GameManager.cs there are several ways we can get a reference to the player in the scene. Personally I like to spawn (ie. gameObject.Instantiate(playerPrefab)) the player in the GameManager. But I'll assume you have your player dragged into the scene so you don't have any reference. Well one way to make a reference to the existing player in the scene is to use Find (https://docs.unity3d.com/ScriptReference/GameObject.Find.html)

Here is a little example code:

GameManager.cs

public class GameManager : MonoBehaviour
{
     PlayerPhys Player;

     void Start()
     {
         Player = GameObject.Find("EXACT PLAYER NAME").GetComponent<PlayerPhys>();
           
         // A different way is to FindObjectByType, it will return the first object it finds with a PlayerPhys component attached 
         Player = FindObjectOfType<PlayerPhys>();
     }
     
     
}

I also make my GameManager class a singleton. https://refactoring.guru/design-patterns/singleton/csharp/example

This way you can easily use this player reference from other scripts for example your enemies.

A very quick intro of how to make GameManager.cs into a singleton is as follows:

public class GameManager : MonoBehaviour
{
     public static GameManager singleton_instance;
     public PlayerPhys Player;

     void Start()
     {
         if (singleton_instance == null)
             singleton_instance =  this;
         else
             Destroy(this);
         Player = GameObject.Find("EXACT PLAYER NAME").GetComponent<PlayerPhys>();
     }
     
     
}

Disclaimer: I am not an expert. Just a indie game dev wannabe you has picked up tricks as I go. Others here can give much more technical and precise help/advice. That said if you have questions about what I wrote here, I will do my best to answer for you.

EDIT: An example of finding the player from within another script such as Enemy.cs:

public class Enemy : MonoBehaviour
{
     void Update()
     {
          // ensure 'Player' in GameManager.cs is declared as public
          Vector3 player_position = GameManager.singleton_instance.Player.tranform.position;
     }
}