c# - Why doesn't "OnTriggerEnter2D()" work when two specific objects collide?

Question

I am creating this flappy bird style game in unity with C#.

I have a scored function in the Game Controller script. Here it is...

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class GameController : MonoBehaviour
{
    private int score = 0;
    public float starScrollSpeed;
    public float groundScrollSpeed;
    public float skyScrollSpeed;
    public GameObject gameOverText;
    public GameObject playAgain;
    public bool gameOver = false;
    public static GameController instance;
    public Text scoreText;

    // Start is called before the first frame update
    void Awake()
    {
        if(instance == null)
        {
            instance = this;
        }

        else if(instance != this)
        {
            Destroy(gameObject);
        }
    }

    // Update is called once per frame

     void Start()
    {
        
    }
    
    void Update()
    {
        
    }

    public void BirdScored()
    {
        if (gameOver)
        {
            return;
        }
        score++;
        scoreText.text = "SCORE  " + score.ToString();
    }

    public void PlaneDestroyed()
    {
        gameOverText.SetActive(true);
        playAgain.SetActive(true);
        gameOver = true;
    }
}

Actually Bird and Plane is the same thing.

What I want to do is to make the bird score/run the BirdScored() function when the Plane overlaps with a star. The Plane has a Rigidbody2D and a collider and stars have a Rigidbody2D but no collider because In the bird script if the plane collide, it destroys.

Here is the Bird Script

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

public class Bird : MonoBehaviour
{
    private bool isDead = false;
    private Rigidbody2D rb2d;
    public float upforce = 200f;
    private Animator anim;

    // Start is called before the first frame update
    void Start()
    {
        rb2d = GetComponent<Rigidbody2D>();
        anim = GetComponent<Animator>();
    }

    // Update is called once per frame
    void Update()
    {

        if (isDead == false)
        {
            if (Input.GetMouseButtonDown(0))
            {
                rb2d.velocity = Vector2.zero;
                rb2d.AddForce(new Vector2(0, upforce));
            }
        }

        anim.SetTrigger("Flap");
    }

    void OnCollisionEnter2D()
    {
        
        isDead = true;
        anim.SetTrigger("Die");
        GameController.instance.PlaneDestroyed();
    }
}

And here is the star script...

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

public class Stars : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        
    }

    // Update is called once per frame
    void Update()
    {
        
    }

    public void OnTriggerEnter2D(Collider2D other)
    {
        if (other.gameObject.name == "Plane")
        {
            GameController.instance.BirdScored();
        }
    }
}

What is wrong and what should I do?

question from:https://stackoverflow.com/questions/65713130/why-doesnt-ontriggerenter2d-work-when-two-specific-objects-collide

Answer 1

Put a Colider2D on the star, and check the Is Trigger option in the inspector.

The Is Trigger is disable the collision with any other collider2d so your plane wont be destroyed by the OnCollisionEnter2D, but the OnTriggerEnter2D will trigger properly.