Collider.OnTriggerEnter(Collider)

Parameters

Description

OnTriggerEnter is called when the Collider other enters the trigger.

This message is sent to the trigger Collider and the Rigidbody (if any) that the trigger Collider belongs to, and to the Rigidbody (or the Collider if there is no Rigidbody) that touches the trigger.

Notes: Trigger events are only sent if one of the Colliders also has a Rigidbody attached. Trigger events will be sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions. OnTriggerEnter occurs on the FixedUpdate after a collision. The Colliders involved are not guaranteed to be at the point of initial contact.

Note: OnTriggerEnter is not technically part of Collision. It is a MonoBehaviour function.

The following CS example shows how a trigger can interact with a sphere GameObject. This GameObject is created in Awake. OnTriggerEnter, OnTriggerStay and OnTriggerExit are called when this cube interacts with the sphere. Update moves the cube forward/back and left/right.

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

public class Example : MonoBehaviour
{
    public bool enter = true;
    public bool stay = true;
    public bool exit = true;
    public float moveSpeed;

    void Awake()
    {
        // move and reduce the size of the cube
        transform.position = new Vector3(0, 0.25f, 0.75f);
        transform.localScale = new Vector3(0.1f, 0.1f, 0.1f);

        // add isTrigger
        var boxCollider = gameObject.AddComponent<BoxCollider>();
        boxCollider.isTrigger = true;

        moveSpeed = 1.0f;

        // create a sphere for this cube to interact with
        GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        sphere.gameObject.transform.position = new Vector3(0, 0, 0);
        sphere.gameObject.AddComponent<Rigidbody>();
        sphere.gameObject.GetComponent<Rigidbody>().isKinematic = true;
        sphere.gameObject.GetComponent<Rigidbody>().useGravity = false;
    }

    void Update()
    {
        transform.Translate(Vector3.forward * Time.deltaTime * Input.GetAxis("Vertical") * moveSpeed);
        transform.Translate(Vector3.right * Time.deltaTime * Input.GetAxis("Horizontal") * moveSpeed);
    }

    private void OnTriggerEnter(Collider other)
    {
        if (enter)
        {
            Debug.Log("entered");
        }
    }

    // stayCount allows the OnTriggerStay to be displayed less often
    // than it actually occurs.
    private float stayCount = 0.0f;
    private void OnTriggerStay(Collider other)
    {
        if (stay)
        {
            if (stayCount > 0.25f)
            {
                Debug.Log("staying");
                stayCount = stayCount - 0.25f;
            }
            else
            {
                stayCount = stayCount + Time.deltaTime;
            }
        }
    }

    private void OnTriggerExit(Collider other)
    {
        if (exit)
        {
            Debug.Log("exit");
        }
    }
}

using UnityEngine;

public class Example : MonoBehaviour
{
    // Destroy everything that enters the trigger
    void OnTriggerEnter(Collider other)
    {
        Destroy(other.gameObject);
    }
}