How do you add an UI EventTrigger by Script ?

Question

The new Unity 4.6 System comes with an EventTrigger System. From the editor this is easy to use but how does one add a trigger, for example for PointerClick, by script (C#) ?

Let's say i have a function called Foo() in a class called ExampleAction on the a child of the gameObject that contains the event trigger. How do i assign now a PointerClick to call ExampleAction.Foo() on that childobject

Thanks!

Answer 1

Best Answer

Answer by Phles · Dec 14, 2014 at 04:38 PM

Hey there, I believe you're after something like this...

 EventTrigger trigger = GetComponentInParent<EventTrigger>();
 EventTrigger.Entry entry = new EventTrigger.Entry();
 entry.eventID = EventTriggerType.PointerClick;
 entry.callback.AddListener( (eventData) => { Foo(); } );
 trigger.delegates.Add(entry);

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Huacanacha · Feb 07, 2015 at 01:02 AM 0

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In researching this myself I noticed that EventTrigger will check every callback for all 12 event types, regardless of whether the callback handles a specific event. I know it's only responding to user initiated UI events so performance isn't critical but it still seems a poor (read inefficient) way to implement this.

Phles · Feb 07, 2015 at 12:27 PM 4

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Indeed, This behaviour is noted in the documentation for EventTrigger, "NOTE: Attaching this component to a GameObject will make that object intercept ALL events, and no event bubbling will occur from this object!"

I think the idea is that EventTrigger is supposed to be simple and easy to use from the inspector, If you want more performance and/or to have unhandled events bubble you can always create your own $$anonymous$$onoBehaviour derived class only implementing the interfaces for event types you actually are going to use... IPointerClickHandler, IPointerEnterHandler ...etc

HugoZandel · Feb 17, 2015 at 03:41 PM 2

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Phles comment is actually the correct answer.

elenzil · Nov 17, 2015 at 11:46 PM 13

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$$anonymous$$or update to this answer: "delegates" has been deprecated; line 5 in the answer should now use "triggers" ins$$anonymous$$d:

 trigger.triggers.Add(entry);

OlivierPons · Jan 18, 2018 at 09:01 AM 1

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Something very important that is not precised: "GetComponentInParent()" will search for a component EventTrigger so there should be an EventTrigger on the object. Click on the object, then "Add Component", then add "Event Trigger" and let it empty, but from now on your code will work.

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Answer 2

Answer by xCyborg · Jul 27, 2015 at 04:49 AM

No he means that:

 newButton.GetComponent<Button>().onClick.AddListener(()=>TestScript());

or:

 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;
  
 public class ClickableButton : MonoBehaviour, IPointerClickHandler {
  
     public void OnPointerClick(PointerEventData eventData)
     {
         if (eventData.button == PointerEventData.InputButton.Left)
             Debug.Log("Left click");
         else if (eventData.button == PointerEventData.InputButton.Middle)
             Debug.Log("Middle click");
         else if (eventData.button == PointerEventData.InputButton.Right)
             Debug.Log("Right click");
     }
 }

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Answer 3

Answer by oferei · Aug 08, 2016 at 09:14 PM

Building on Phles's answer, here's pretty much the same code, neatly wrapped in a function:

 public static void AddEventTriggerListener(EventTrigger trigger,
                                            EventTriggerType eventType,
                                            System.Action<BaseEventData> callback)
 {
     EventTrigger.Entry entry = new EventTrigger.Entry();
     entry.eventID = eventType;
     entry.callback = new EventTrigger.TriggerEvent();
     entry.callback.AddListener(new UnityEngine.Events.UnityAction<BaseEventData>(callback));
     trigger.triggers.Add(entry);
 }

You could use it like this, for example:

     AddEventTriggerListener(
         GetComponent<EventTrigger>(),
         EventTriggerType.PointerClick,
         OnClicked);

 // Callback function
 void OnClicked(BaseEventData eventData) {
     PointerEventData pointerEventData = (PointerEventData)eventData;
     Debug.Log("Click: pointerEventData=" + pointerEventData);
 }

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ben-rasooli · Dec 07, 2017 at 11:39 PM 0

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Just wondering if line 7 requires! entry.callback = new EventTrigger.TriggerEvent();

booferei ben-rasooli · Dec 17, 2017 at 10:08 AM 0

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Not 100%. I see you've added a similar answer without it. So I guess not?

booferei ben-rasooli · Sep 12, 2018 at 09:00 AM 0

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Apparently the following line is not necessary (line 7 in my original answer above):

entry.callback = new EventTrigger.TriggerEvent();

Answer 4

I've made an extension method for it. Simply include this class somewhere in your project:

 using UnityEngine.EventSystems;
 
 public static class ExtensionMethods
 {
     public static void AddListener (this EventTrigger trigger, EventTriggerType eventType, System.Action<PointerEventData> listener)
     {
         EventTrigger.Entry entry = new EventTrigger.Entry();
         entry.eventID = eventType;
         entry.callback.AddListener(data => listener.Invoke((PointerEventData)data));
         trigger.triggers.Add(entry);
     }
 }

Then use it like this:

 using UnityEngine;
 using UnityEngine.EventSystems;
 
 public class UIController : MonoBehaviour
 {
     void Start ()
     {
         EventTrigger myEventTrigger = GetComponent<EventTrigger> (); //you need to have an EventTrigger component attached this gameObject
         myEventTrigger.AddListener (EventTriggerType.PointerClick, onClickListener);
     }
 
     void onClickListener (PointerEventData eventData)
     {
         //put your logic here...
     }
 }

Answer 5

My realization of the extension method that takes into account if there is already such event type. Also, there are methods for removing listeners.

 using UnityEngine.Events;
 using UnityEngine.EventSystems;
 
 public static class EventTriggerExtensions
 {
     public static void AddListener(this EventTrigger eventTrigger, EventTriggerType triggerType,
         UnityAction<BaseEventData> call)
     {
         if (eventTrigger == null)
             throw new ArgumentNullException(nameof(eventTrigger));
         if (call == null)
             throw new ArgumentNullException(nameof(call));

         EventTrigger.Entry entry = eventTrigger.triggers.Find(e => e.eventID == triggerType);
         if (entry == null)
         {
             entry = new EventTrigger.Entry {eventID = EventTriggerType.PointerClick};
             eventTrigger.triggers.Add(entry);
         }

         entry.callback.AddListener(call);
     }

     public static void RemoveListener(this EventTrigger eventTrigger, EventTriggerType triggerType,
         UnityAction<BaseEventData> call)
     {
         if (eventTrigger == null)
             throw new ArgumentNullException(nameof(eventTrigger));
         if (call == null)
             throw new ArgumentNullException(nameof(call));

         EventTrigger.Entry entry = eventTrigger.triggers.Find(e => e.eventID == triggerType);
         entry?.callback.RemoveListener(call);
     }

     public static void RemoveAllListeners(this EventTrigger eventTrigger, EventTriggerType triggerType)
     {
         if (eventTrigger == null)
             throw new ArgumentNullException(nameof(eventTrigger));

         EventTrigger.Entry entry = eventTrigger.triggers.Find(e => e.eventID == triggerType);
         entry?.callback.RemoveAllListeners();
     }
 }

How do you add an UI EventTrigger by Script ?

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