Collider.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.

Note: Both GameObjects must contain a Collider component. One must have Collider.isTrigger enabled, and contain a Rigidbody. If both GameObjects have Collider.isTrigger enabled, no collision happens. The same applies when both GameObjects do not have a Rigidbody component.

To use the following code sample, create a primitive GameObject, and attach a Collider and Rigidbody component to it. Enable Collider.isTrigger and Rigidbody.isKinematic. When the primitive collides, OnTriggerEnter gets called. In this example, the direction immediately reverses. When the GameObject exits the collision, Unity calls OnTriggerExit, changing the color.

using UnityEngine;

public class exampleScript : MonoBehaviour
{
    private float speed = 2f;
    Renderer rend;
    int colorPicker = 0;

    private void Start()
    {
        rend = GetComponent<Renderer>();
        transform.position = Vector3.zero;
        transform.rotation = Quaternion.Euler(0, 90, 0);

        //Create two GameObjects to act as walls
        GameObject leftWall = GameObject.CreatePrimitive(PrimitiveType.Cube);
        GameObject rightWall = GameObject.CreatePrimitive(PrimitiveType.Cube);
        //Move the walls to the correct positions
        leftWall.transform.position = new Vector3(-10, 0, 0);
        rightWall.transform.position = new Vector3(10, 0, 0);
        //Scale the walls
        leftWall.transform.localScale = new Vector3(1, 2, 1);
        rightWall.transform.localScale = new Vector3(1, 2, 1);
    }

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

    //When the Primitive collides with the walls, it will reverse direction
    private void OnTriggerEnter(Collider other)
    {
        speed = speed * -1;
        colorPicker = Random.Range(0, 10);
    }

    //When the Primitive exits the collision, it will change Color
    private void OnTriggerExit(Collider other)
    {
        switch (colorPicker)
        {
            case 0: rend.material.color = Color.white; break;
            case 1: rend.material.color = Color.cyan; break;
            case 2: rend.material.color = Color.blue; break;
            case 3: rend.material.color = Color.black; break;
            case 4: rend.material.color = Color.red; break;
            case 5: rend.material.color = Color.green; break;
            case 6: rend.material.color = Color.grey; break;
            case 7: rend.material.color = Color.magenta; break;
            case 8: rend.material.color = Color.yellow; break;
            case 9: rend.material.color = Color.gray; break;
        }
    }
}