OnCollision events

Collision events occur when two non-trigger collidersAn invisible shape that is used to handle physical collisions for an object. A collider doesn’t need to be exactly the same shape as the object’s mesh - a rough approximation is often more efficient and indistinguishable in gameplay. More info
See in Glossary make contact.

Example uses for collisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a Rigidbody component and is in motion. More info
See in Glossary events include:

• When a projectile hits a target, destroy both the projectile and the enemy.
• When a player character touches a door, trigger an animation to open the door.
• When a player character touches a power-up, increase the player’s size.

Working with collision events primarily involves the following API functions:

• Collider.OnCollisionEnter: Unity calls this function on each collider when two colliders first make contact.
• Collider.OnCollisionStay: Unity calls this function on each collider once per physics update while two colliders are in contact.
• Collider.OnCollisionExit: Unity calls this function on each collider when two colliders cease contact.

For collision events, at least one of the objects involved must have a dynamic physics body (that is, a Rigidbody or ArticulationBody that has Is Kinematic disabled). If both GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary in a collision are kinematic physics bodies, the collision does not call OnCollision functions.

The following example prints a message to the console when Unity calls each function.

using UnityEngine;
using System.Collections;

public class DoorObject : MonoBehaviour
{
    // “other” refers to the collider that is touching this collider
    void OnCollisionEnter (Collider other)
    {
        Debug.Log ("A collider has made contact with the DoorObject Collider");
    }

    void OnCollisionStay (Collider other)
    {
        Debug.Log ("A collider is in contact with the DoorObject Collider");
    }
    
    void OnCollisionExit (Collider other)
    {
        Debug.Log ("A collider has ceased contact with the DoorObject Collider");
    }
}

For examples of practical applications for OnCollision events, refer to example scripts for collider events.