[uGUI] Fix GraphicRaycaster Failing to Detect Nested UI Elements

Solution

raycastingCanvasEvent Systeminput

Unity 2021.x - Unity 6.3.x

Published Sat, Mar 28

Reviewed by _architect

Chief Editor

80 posts

Issue

A common issue arises when UI elements, despite having an Image component with the Raycast Target property enabled, are not registered by a GraphicRaycaster. This typically occurs when a nested Canvas exists without its own raycaster, causing the EventSystem to ignore that hierarchy branch even if the Raycast Target is active.

UI elements with Raycast Target checked may fail to detect raycasts if a nested Canvas component is present without a GraphicRaycaster on the same GameObject.

Explanation

The primary cause for GraphicRaycaster failing to detect a UI element, especially when Raycast Target is enabled on its Image component, is the presence of an additional Canvas component on your UI element or one of its parent GameObjects. Every Canvas boundary defines a new independent raycasting scope.

When a nested Canvas is introduced for sorting or optimization, the GraphicRaycaster on the parent Canvas stops descending into that hierarchy branch. To resolve this, each nested Canvas must be accompanied by its own GraphicRaycaster component.

Identify the GameObject failing to receive input events in the hierarchy.
Check for any parent GameObject containing a Canvas component between the element and the root.
If a nested Canvas is found, attach a GraphicRaycaster component to that same GameObject.
Ensure the CanvasGroup on the element or any parent does not have Blocks Raycasts disabled.

Additional Tips

Utilize the EventSystem debugger in the Inspector to see which object is currently being pointed at in real-time.
Check if the Canvas Render Mode requires an Event Camera to be manually assigned for raycasts to work in World Space.

Copy


using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
using System.Collections.Generic;

public class UiInteractionHandler : MonoBehaviour
{
    [SerializeField] private GraphicRaycaster _raycaster;
    [SerializeField] private EventSystem _eventSystem;

    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            PointerEventData pointerEventData = new PointerEventData(_eventSystem);
            pointerEventData.position = Input.mousePosition;

            List<RaycastResult> results = new List<RaycastResult>();
            _raycaster.Raycast(pointerEventData, results);

            if (results.Count > 0)
            {
                foreach (RaycastResult result in results)
                {
                    Debug.Log("Hit UI GameObject: " + result.gameObject.name);
                }
            }
            else
            {
                Debug.Log("No UI elements hit.");
            }
        }
    }
}

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[uGUI] Fix GraphicRaycaster Failing to Detect Nested UI Elements