How can I get an UI object below the mouse in Unity?

Question

I am currently trying to make a drag and drop system where i have a dragable UI object which i can place on a other object. But i don't know how i can get the UI object below the mouse and the dragable UI object.

This is the code of my dragableObject:

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

public class DragHandeler : MonoBehaviour, IBeginDragHandler, IDragHandler, 
IEndDragHandler
{
  public Transform parentToReturnTo = null;
  public Transform placeHolderParent = null;


  public void OnBeginDrag(PointerEventData eventData)
  {
      parentToReturnTo = transform.parent;
  }

  public void OnDrag(PointerEventData eventData)
  {
      transform.position = eventData.position;

  }

  public void OnEndDrag(PointerEventData eventData)
  {
      transform.position = parentToReturnTo.position;
  }
}

and this code for my place holder:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 public class PlaceHolder : MonoBehaviour, IDropHandler, 
 IPointerEnterHandler, IPointerExitHandler
 {
    public void OnPointerEnter(PointerEventData eventData)
    {
         Transform test = eventData.pointerDrag.GetComponent<Transform>();
        Debug.Log(test.name);
    }

    public void OnPointerExit(PointerEventData eventData)
    {
    }

    public void OnDrop(PointerEventData eventData)
   {
   }
}

the problem is the OnPointerEnter Function isn't called always when it should be, it only calls it sometimes when i am over the object with my mouse. Is there maybe a other way on how i can get the current object below the dragable object?

Answer 1

So, the issue is that your 'draggable' is blocking the raycast for any objects behind that object, and as a result - your PlaceHolder doesn't triggering any events because a ray is always blocked by your 'draggable'. The easiest solution is just disable raycastTarget property at the beginning of the drag and re-enable it at the end of drag.

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

public class DragHandeler : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
  public Transform parentToReturnTo = null;
  public Transform placeHolderParent = null;

  public void OnBeginDrag(PointerEventData eventData)
  {
      // disable 'raycast target' for your draggable object
      GetComponent<Image>().raycastTarget = false;

      parentToReturnTo = transform.parent;
  }

  public void OnDrag(PointerEventData eventData)
  {
      transform.position = eventData.position;
  }

  public void OnEndDrag(PointerEventData eventData)
  {
      // enable it back when drag is over
      GetComponent<Image>().raycastTarget = true;

      transform.position = parentToReturnTo.position;
  }
}