拖动对象时会跳到中心答案

【问题标题】：Object jumps to the center when dragging it拖动对象时会跳到中心
【发布时间】：2018-10-29 19:11:37
【问题描述】：

您如何使用IBeginDragHandler 并设置拖动位置以保持一致而不是突然切换到游戏对象的中心？

这是我的简单代码，用于抓取和反对并将它们释放到新位置。但是，我意识到通过角落抓取对象（2D）会自动将指针设置为中心。像这样离开拖累感觉很糟糕。

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

public class Draggable : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler {
    public void OnBeginDrag(PointerEventData eventData) {
        Debug.Log ("Started dragging");

    }

    public void OnDrag(PointerEventData eventData) {
        Debug.Log ("Currently dragging");
        this.transform.position = eventData.position;
    }

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

}

【问题讨论】：

标签： c# unity3d drag-and-drop draggable

【解决方案1】：

您需要使用偏移量。调用OnPointerDown 时获取偏移量。在调用 OnDrag 时应用此偏移量。

对于 2D 精灵：

Camera mainCamera;
float zAxis = 0;
Vector3 clickOffset = Vector3.zero;

// Use this for initialization
void Start()
{
    zAxis = transform.position.z;
}

public void OnPointerDown(PointerEventData eventData)
{
    clickOffset = transform.position - mainCamera.ScreenToWorldPoint(new Vector3(eventData.position.x, eventData.position.y, zAxis));
}

public void OnDrag(PointerEventData eventData)
{
    //Use Offset To Prevent Sprite from Jumping to where the finger is
    Vector3 tempVec = mainCamera.ScreenToWorldPoint(eventData.position) + clickOffset;
    tempVec.z = zAxis; //Make sure that the z zxis never change

    transform.position = tempVec;
}

public void OnEndDrag(PointerEventData eventData)
{

}

对于 UI 对象，偏移量仍然是相同的解决方案，但也应使用 ScreenPointToLocalPointInRectangle。

public class Draggable : MonoBehaviour, IDragHandler, IBeginDragHandler
{
    public Canvas parentCanvas;
    Vector3 Offset = Vector3.zero;

    public void OnPointerDown(PointerEventData eventData)
    {
        Vector2 pos;
        RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvas.transform as RectTransform, eventData.position, parentCanvas.worldCamera, out pos);
        Offset = transform.position - parentCanvas.transform.TransformPoint(pos);
    }

    public void OnDrag(PointerEventData eventData)
    {
        Vector2 movePos;
        RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvas.transform as RectTransform, eventData.position, parentCanvas.worldCamera, out movePos);
        transform.position = parentCanvas.transform.TransformPoint(movePos) + Offset;
    }
}

【讨论】：