MonoBehaviour.OnTriggerEnter(Collider)

Parameters

Description

When a GameObject collides with another GameObject, Unity calls OnTriggerEnter.

OnTriggerEnter happens on the FixedUpdate function when two GameObjects collide. The Colliders involved are not always at the point of initial contact.

Both GameObjects must contain a Collider component. At least one of the colliders must be a trigger collider and at least one must be a physics body collider. For more information refer to Interaction between collider types.

using UnityEngine;

public class Example : MonoBehaviour
{
    private float speed = 2f;

    //Moves this GameObject 2 units a second in the forward direction
    void Update()
    {
        transform.Translate(Vector3.forward * Time.deltaTime * speed);
    }

    //Upon collision with another GameObject, this GameObject will reverse direction
    private void OnTriggerEnter(Collider other)
    {
        speed = speed * -1;
    }
}