OnDrag does not work, but OnMouseDown works

Question

There is a code:

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

public class DragAndDropGame : MonoBehaviour, IBeginDragHandler, IDragHandler
{

    Camera MainCamera;

    void Awake()
    {
        MainCamera = Camera.allCameras[0];
        Debug.Log(MainCamera);
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        Debug.Log("OnBeginDrag");
    }

    public void OnDrag(PointerEventData eventData)
    {
        Vector3 newPos = MainCamera.ScreenToWorldPoint(eventData.position);
        newPos.z = 0;
        transform.position = newPos;
    }

    void OnMouseDown()
    {
        Debug.Log("OnMouseDown");
    }
}

OnMouseDown fulfills, but the implementation ofIBeginDragHandler, IDragHandler - not. What can be wrong?

Answer 1

IDragHandler (and its associates) are only called for UI elements that are part of a canvas. And even then, only for UI components (Image, text, etc) and not 3D objects and colliders.

You are probably looking for OnMouseDrag.

Answer 2

You probably implemented IDragHandler, but forgot to implement IBeginDragHandler and IEndDragHandler.

All three must be implemented, otherwise OnDrag(PointerEVentData eventData) will not be called for you.

For example, this will be ok:

public class Skins_TouchingArea_UI : MonoBehaviour, IBeginDragHandler, IEndDragHandler, IDragHandler{

    public void OnDrag(PointerEventData eventData){  Debug.Log("dragging"); }

    //required for OnDrag() to work
    public void OnBeginDrag(PointerEventData eventData) {}

    //required for OnDrag() to work
    public void OnEndDrag(PointerEventData eventData) {}
}

Answer 3

Try adding this namespace:

using UnityEngine.UI