Unity Engine - Instantiate a prefab by collision

Question

I have a GameObject called Player. Attached to Player there is a script component called Player ( same ) Inside the Player's script, I have a field called _weaponPrefab ( GameObject type )

In the Inspector, I can easily drag & drop any prefabs from my Prefab folder, inside the _weaponPrefab variable.

All good so far. What I want to archive is: to be able to add my Prefabs based on a Collision2D. So if my Player collides with a Prefab, let's say a Sword, the prefab of that sword will be automatically attached and insert into the _weaponPrefab field inside the Player script.

Below my Player script:

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

public class Player : MonoBehaviour
{
    [SerializeField] private float _speed = 5.0f;
    [SerializeField] private float _fireRate = 0.2f;
                     private bool _canFire = true;


    [SerializeField] private GameObject _weaponPrefab; <- to populate runtime


    // Use this for initialization
    void Start ()
    {
        transform.position = Vector3.zero;
    }

    // Update is called once per frame
    void Update ()
    {
        if (Input.GetKeyDown(KeyCode.Space) && _canFire)
            StartCoroutine(Shoot());
    }


    void OnTriggerEnter2D(Collider2D other)
    {
        //here i don't know how to continue.

    }

    public IEnumerator Shoot()
    {
        _canFire = false;
        Instantiate(_weaponPrefab, transform.position + new Vector3(0, 1, 0), Quaternion.identity);
        yield return new WaitForSeconds(_fireRate);
        _canFire = true;
    }
}

Edit: i just wrote a comment of where i don't know how to proceed.

Answer 1

When you instantiate a GameObject you need to pass basically 3 parameters (However not all of them are mandatory, check):

• The prefab
• The position
• The rotation

Let's assume you have a placeholder in the hand or in the back of your character, to keep there the weapon once collected. This placeholder can be an empty gameobject (no prefab attached, but will have a transform.position component)

Now let's assume you have a list of weapons in the scene with their prefab and with a different tag each. Then you can do something like this:

GameObject weapon;
GameObject placeholder;

public Transform sword;
public Transform bow;
...


void OnTriggerEnter2D(Collider2D other)
{
    //You can use a switch/case instead
    if(other.gameObject.tag == "sword"){
        Instantiate(sword, placeholder.transform.position, Quaternion.identity);
    }else if(other.gameObject.tag == "bow"){
        Instantiate(bow, placeholder.transform.position, Quaternion.identity);
    }...

}

Answer 2

There are many ways to accomplish what you desire.

My suggestion may be out of your comfort zone at first, but it will provide you with most flexibility and eventually easy of programming/ designing/ maintaining your game (in my opinion).

First make a scriptable object (what is a scriptable object and how do i use it?)

using UnityEngine;
using System.Collections;
using UnityEditor;

public class Item
{
    [CreateAssetMenu(menuName = "new Item")]
    public static void CreateMyAsset()
    {
        public GameObject prefab;
        // you can add other variables here aswell, like cost, durability etc.
    }
}

Create a new item (in Unity, Assets/new Item)

Then create a monobehaviour script which can hold the item. In your case let's name it "Pickup".

public class Pickup : MonoBehaviour
{
    public Item item;
}

Finally in your player script, change your on TriggerEnter to:

void OnTriggerEnter2D(Collider2D other)
{
    if(other.GetComponentInChildren<Pickup>())
    {
        var item = other.GetComponentInChildren<Pickup>().item;
        _weaponPrefab = item.prefab;
    }

}

Answer 3

What I'll do is load the prefabs first in a Dictionary<string, GameObject> from the resources folder.

First I populate the dictionary with all the weapon prefabs in the Start method with the tag of the object as a key. Then in the OnTriggerEnter2D I check if the tag is in the dictionary then I instantiate it from there.

Take a look at the code :

private Dictionary<string, GameObject> prefabs;

// Use this for initialization
void Start () {
    var sword = (GameObject) Resources.Load("Weapons/sword", typeof(GameObject));
    prefabs.Add("sword", sword);
    // Add other prefabs
};

void OnTriggerEnter2D(Collider2D other)
{
    if (prefabs.ContainsKey(other.tag))
        Instantiate(prefabs[other.tag]);
}

NOTE : your prefabs needs to be in the folder Assets/Resources/Weapons because I used Resources.Load("Weapons/sword", typeof(GameObject));