By design, OnTriggerExit isn’t called if the object that was responsible for OnTriggerEnter is disabled or destroyed. The result is you can get OnTriggerEnter without ever getting OnTriggerExit, and can get OnTriggerEnter multiple times for the same object, for example if the object that caused the trigger was deactivated and then activated again
This is bad design and breaks some optimization techniques such as adding objects in a zone to a HashSet when they enter the zone and removing them when they leave.
Others have suggested hacks, such as moving the object and waiting one frame before destroying it.
Here is a fix that is robust, doesn’t require hacks, and was designed to be fast and easy to use.
It requires you to call
ReliableOnTriggerExit.NotifyTriggerEnter(other, gameObject, OnTriggerExit);
and
ReliableOnTriggerExit.NotifyTriggerExit(other, gameObject);
every time you use OnTriggerEnter() and want to be sure you’ll get OnTriggerExit()
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
// OnTriggerExit is not called if the triggering object is destroyed, set inactive, or if the collider is disabled. This script fixes that
//
// Usage: Wherever you read OnTriggerEnter() and want to consistently get OnTriggerExit
// In OnTriggerEnter() call ReliableOnTriggerExit.NotifyTriggerEnter(other, gameObject, OnTriggerExit);
// In OnTriggerExit call ReliableOnTriggerExit.NotifyTriggerExit(other, gameObject);
//
// Algorithm: Each ReliableOnTriggerExit is associated with a collider, which is added in OnTriggerEnter via NotifyTriggerEnter
// Each ReliableOnTriggerExit keeps track of OnTriggerEnter calls
// If ReliableOnTriggerExit is disabled or the collider is not enabled, call all pending OnTriggerExit calls
public class ReliableOnTriggerExit : MonoBehaviour
{
public delegate void _OnTriggerExit(Collider c);
Collider thisCollider;
bool ignoreNotifyTriggerExit = false;
// Target callback
Dictionary<GameObject, _OnTriggerExit> waitingForOnTriggerExit = new Dictionary<GameObject, _OnTriggerExit>();
public static void NotifyTriggerEnter(Collider c, GameObject caller, _OnTriggerExit onTriggerExit)
{
ReliableOnTriggerExit thisComponent = null;
ReliableOnTriggerExit[] ftncs = c.gameObject.GetComponents<ReliableOnTriggerExit>();
foreach (ReliableOnTriggerExit ftnc in ftncs)
{
if (ftnc.thisCollider == c)
{
thisComponent = ftnc;
break;
}
}
if (thisComponent == null)
{
thisComponent = c.gameObject.AddComponent<ReliableOnTriggerExit>();
thisComponent.thisCollider = c;
}
// Unity bug? (!!!!): Removing a Rigidbody while the collider is in contact will call OnTriggerEnter twice, so I need to check to make sure it isn't in the list twice
// In addition, force a call to NotifyTriggerExit so the number of calls to OnTriggerEnter and OnTriggerExit match up
if (thisComponent.waitingForOnTriggerExit.ContainsKey(caller) == false)
{
thisComponent.waitingForOnTriggerExit.Add(caller, onTriggerExit);
thisComponent.enabled = true;
}
else
{
thisComponent.ignoreNotifyTriggerExit = true;
thisComponent.waitingForOnTriggerExit[caller].Invoke(c);
thisComponent.ignoreNotifyTriggerExit = false;
}
}
public static void NotifyTriggerExit(Collider c, GameObject caller)
{
if (c == null)
return;
ReliableOnTriggerExit thisComponent = null;
ReliableOnTriggerExit[] ftncs = c.gameObject.GetComponents<ReliableOnTriggerExit>();
foreach (ReliableOnTriggerExit ftnc in ftncs)
{
if (ftnc.thisCollider == c)
{
thisComponent = ftnc;
break;
}
}
if (thisComponent != null && thisComponent.ignoreNotifyTriggerExit == false)
{
thisComponent.waitingForOnTriggerExit.Remove(caller);
if (thisComponent.waitingForOnTriggerExit.Count == 0)
{
thisComponent.enabled = false;
}
}
}
private void OnDisable()
{
if (gameObject.activeInHierarchy == false)
CallCallbacks();
}
private void Update()
{
if (thisCollider == null)
{
// Will GetOnTriggerExit with null, but is better than no call at all
CallCallbacks();
Component.Destroy(this);
}
else if (thisCollider.enabled == false)
{
CallCallbacks();
}
}
void CallCallbacks()
{
ignoreNotifyTriggerExit = true;
foreach (var v in waitingForOnTriggerExit)
{
if (v.Key == null)
{
continue;
}
v.Value.Invoke(thisCollider);
}
ignoreNotifyTriggerExit = false;
waitingForOnTriggerExit.Clear();
enabled = false;
}
}
